Led with upstanding nanowire structure and method of producing such

The present invention relates to light emitting diodes, i.e. LEDs. In particular, the present invention relates to nanostructured LED devices having nanostructured arrays.

The types of light emitting diodes (LEDs) that are popular today are built on planar technology. By configuring the PN junction as multiple layers on the substrate, the device can be basically horizontal. Photogeneration and recombination occurs in a subset of these layers. Since the semiconductor layer has a refractive index substantially higher than that of air, a considerable amount of the generated light is reflected in the layer and does not contribute to effective light emission of the device. In fact, the layer behaves like a light guide in the horizontal plane of the LED. Measures have been proposed to mitigate the influence of LED light confined in the device and efficiently extract light from the semiconductor layer. Such measures include changing the surface so that the part takes various angles with respect to the horizontal plane. A similar approach is proposed in European Patent Publication No. 1369935, in which nano-sized particles are applied to LED devices to diffuse light or to absorb light to produce light of different wavelengths. It is equipped. In addition, planar technology imposes constraints in terms of minimization and selection of suitable materials, as further described below.

Improvements in nanoscale technology, and in particular the ability to manufacture nanowires, have opened up the possibility of designing structures and combining materials that planner technology could not. One of the cornerstones of this development is that the 1D properties of nanowires have made it possible to eliminate the need for lattice matching between dissimilar materials in devices made with planar technology. For example, InP nanowires have been shown and used to be able to grow defect-free on InAs or Si. U.S. Patent Publication No. 2004007546 by Samuelson et al. Discloses a plurality of devices based on nanowire structures, such as nanowire LEDs. These LEDs have an internal heterostructure that provides a quantum confinement effect.

U.S. Patent Publication No. 20030168964 discloses multiple nanowire components that act as LEDs mounted together between a conductive transparent substrate at the bottom of the nanowire and a transparent cover substrate at the top. Each individual nanowire has a P-type, N-type, and light-emitting layer structure. Nanowires are said to be configured to emit light through a conductive, transparent substrate.

Other nanowire LEDs have also been reported so far. Hiruma et al. Produced a vertical GaAs nanowire pnLED. As described in "P-n Junction of GaAs formed in quantum crystals" by Haraguchi et al., Appl. Phys. Lett. 60 (6) 1992, nanowires are embedded in SOG and by Au / Ge / Ni top contacts. It is covered. These devices showed electrocooled light at room temperature. GaN-based nanowire LEDs can be manufactured as described in "Core / Multishell Nanowire Heterostrucrure as Multicolor, High-Efficiency Light-Emitting Diodes" by Quian et al.

Outline of the present invention It has been shown that this technique can use nanostructures to construct LED devices. Further improvements in efficiency are needed to take full advantage of the potential offered by nanotechnology.

An object of the present invention is to provide a nanostructured LED device and a method for manufacturing the same, which can solve the shortcomings of conventional devices and methods. This can be achieved by the device defined in claim 1 and the method defined in claim 23.

The nanostructured LED device according to the present invention has a plurality of independent nanostructured LED arrays. Each nanostructured LED has an active region for light emission. Nanostructured LED devices further have one independent nanostructured LED, or multiple reflectors coupled into a group of nanostructured LEDs. Each reflector has a concave surface facing the active region of each independent nanostructured LED, or the active region of a group of nanostructured LEDs.

As the nanostructured LED device according to the present invention, a device including an LED array layer and a reflector layer can be seen. The plurality of nanostructured LEDs forms an LED array layer having a plurality of corresponding active regions, which is configured in the LED array layer. The reflector layer is configured in a plane parallel to the LED array layer, each having a concave surface facing the active region of one or a group, and configured to direct light through the LED array. Includes reflectors. The reflector cycle of the reflector layer may be related to the cycle of the nanostructured LED, or the active region associated with it.

In one embodiment of the invention, each reflector covers the top surface and, in some cases, a portion of the side surface of an elongated nanostructured LED, typically an LED formed from nanowires.

According to one embodiment, the nanostructured LED has a pyramid shape, and the reflector basically covers all surfaces of the nanostructured LED except for the side surface on the substrate side.

Individual reflectors may be connected to form a layer of continuous reflection. In one embodiment, the continuous reflective layer covers both the top surface of the nanostructured LED and the packed bed provided to fill the space between the nanostructures.

A reflector or continuous reflective layer may be supplied directly to the nanostructured LED. Alternatively, a spacer material may be inserted between them to determine the shape of the reflector. Also, a contact or contact layer may be placed between the reflector and the nanostructured LED. In another example, a continuously reflective layer is used as the top contact to the nanostructured LED.

One of the advantages of the present invention is that the efficiency of nanostructured LED devices can be sufficiently increased. A further advantage is that nanostructured LED devices can be manufactured by default methods.

Further, a further advantage of the nanostructured LED of the present invention is that the production can be applied to cost-effective industrial production.

Embodiments of the present invention are defined by the dependent claims. Other objects, advantages, and novel features of the invention will become apparent from the detailed description of the invention set forth below, taking into account the accompanying drawings and claims.

<figref num="1a">FIG. 1a is a diagram showing an outline of a nanostructured LED device according to the present invention.</figref><figref num="1b">、</figref><figref num="1c">、</figref><figref num="1d">、</figref><figref num="1e">1b to 1e are diagrams showing upright individual nanostructured LEDs used in the nanostructured LED device according to the present invention.</figref><figref num="2">2a) to 2f) are diagrams showing an outline of the reflector of the present invention.</figref><figref num="3a">、</figref><figref num="3b">、</figref><figref num="3c">3a-c are diagrams schematically showing different embodiments of the nanostructured LED device having the reflector according to the present invention.</figref><figref num="4a">、</figref><figref num="4b">4a to 4b are diagrams schematically showing an embodiment of a nanostructured LED including the nanostructured LED device according to the present invention.</figref><figref num="5a">、</figref><figref num="5b">、</figref><figref num="5c">5a to 5c are diagrams schematically showing embodiments of the nanostructured LED device according to the present invention.</figref><figref num="6">FIG. 6 is a diagram showing basic manufacturing steps in the method according to the present invention.</figref><figref num="7">FIG. 7 is a diagram schematically showing an LED nanostructure.</figref><figref num="8a">FIG. 8a is an SEM image of the nanostructured LED of FIG.</figref><figref num="8b">FIG. 8b is an image of the active LED nanostructure.</figref><figref num="9">FIG. 9 is an SEM image of the nanowire structure of the present invention after the first MOVPE step.</figref><figref num="10">10a-c are graphs of photoluminescence of nanowire and LED nanostructures according to FIGS. 7 and 9.</figref><figref num="11">FIG. 11 shows a) the electroluminescence-dependent power of a GaAs LED grown on GaP and Si, and b) an EL spectrum at 80 mA from a GaP and Si-based LED nanostructure.</figref><figref num="12">Figures 12a-c show SEM images of selectively grown nanostructures of different shapes.</figref><figref num="13">Figures 13a-b show SEM images of two different shapes of the LED structure.</figref>

Preferred embodiments of the present invention will be described with reference to the drawings.

Detailed explanation The nanostructured light emitting diode according to the present invention, that is, an LED device, includes an upright nanostructured LED. Individual nanostructured LEDs are formed, for example, by using nanowires. Nanowires are used as active elements in LEDs or as essential materials for nanostructures, and by using nanowires, for example, nanostructures can be manufactured using materials that are not suitable for substrate materials. Suitable methods for growing nanowires on semiconductor substrates are described in US Patent Publication No. 2003010244. A method of providing epitaxially grown nanowires with a heterostructure is disclosed in US Patent Publication No. 20040075464. Nanostructured LEDs are used as an InGaN / GaN hexagonal pyramid structure on a GaN substrate, as shown in other methods, such as "Spatialcontrol of InGaNluminescence by MOCVD selective epitaxy" by D. Kapolnek et al., Crystal Growth 189/190 (1998) 83-86. It may be formed.

For the purposes of this application, upright nanowires should be construed as nanowires protruding from the substrate at some angle. Upright nanowires, for example, epitaxially grow from a substrate. The angle formed with the substrate typically varies depending on the material contained in the substrate and nanowires, the surface of the substrate, and the growth conditions. By controlling these parameters, it is possible to manufacture nanowires that point in one direction, such as the vertical direction, or a limited set of directions. For example, if the nanowires and substrates are made of zinc ore and diamond semiconductors consisting of the elements of Group 3, Group 5, and Group 4 of the Periodic Table column, such nanowires grow in the [111] direction. It is possible to grow in a direction perpendicular to the surface of any {111} substrate. The other directions given as the angle between the normal to the surface and the axial direction of the nanowires are 70,53 ° {111}, 54,73 ° {100}, 35,27 ° {110}, and 90 ° {110. }including. Therefore, nanowires define one or a limited set of orientations.

All references such as top, top, bottom, down, etc. are made by considering the substrate at the bottom and the nanowires extending upward from the substrate. Vertical refers to the direction parallel to the longitudinal direction of the nanowires, and horizontal refers to the direction parallel to the plane formed by the substrate. This term is used for ease of understanding and does not limit a particular assembly orientation. FIG. 1a schematically illustrates the nanostructured LED device 101 according to the present invention, which includes at least one array of nanostructured LEDs 100, each having an individual active region 120 that produces light. Nanostructured LEDs grow from substrate 105 during manufacturing. The nanostructured LED device 101 according to the present invention is designed to be generally referred to as a "flip-flop" structure, and light is extracted through the substrate 105. In another example, the substrate is removed during manufacturing and light is emitted directly from the nanostructured LED100 or through a buffer layer or a protective layer (not shown) that covers the underside of the nanostructured LED100. According to the present invention, the light produced is at least in part at the opposite end of the nanostructured LED, which is closer to the top end, that is, the light leaves the device as compared to the nanostructured LED. Aimed by the reflector 135 in a closer position. The reflector 135 aims or focuses the light from the active region in the direction of the substrate. Aiming the nanostructured LED array and the light directed in the normal direction of the substrate plane reduces internal reflections, which is advantageous for light extraction of the device. Highly directional emission is advantageous for some LED applications. Since the reflector 135 has a basic concave surface facing the active region 120, the light can be aimed. Here, as shown in FIG. 2, the concave surface is not limited to these, but is a continuous curved surface (a), an open rectangle (b), an open rectangle with rounded corners (c), and a plurality of concave surfaces. It should be interpreted in a very broad way, including cross-sections that connect straight parts of (d) at different angles, two legs of a triangle (e), or multiple continuous curves (f). .. Aiming should also be broadly interpreted, including that the light leaving the LED device does not have to be exactly horizontal, but is generally directed in the preferred direction.

The reflector may be deposited as a highly reflective metal layer on top of the structure formed during growth and / or subsequent treatment. Typical reflector materials are, but are not limited to, Ag, Al (for LEDs in the green and blue range with a wavelength of λ &lt;500 nm), LEDs in the infrared, red, orange, and amber regions. Includes the same and au for. Further, for example, a multi-layer structure including a repeating layer of algaas / gaas or gan / algan may be used as a reflector. Reflector deposition methods include, but are not limited to, vapor deposition, sputtering, electroplating or electroless plating. To protect the reflector from corrosion and oxidation, for example, sio₂, Si₃N₄, Or an additional protective insulating layer may be formed from a similar material. An opening may be made in this layer to provide an electrical connection to the reflector.

The dimensions of the individual reflectors in the nanostructured LED device according to the present invention vary greatly depending on the embodiment, and at least do not vary depending on the size and shape of the individual nanostructured LEDs. The typical diameter and height range is the widest, ranging from 1/10 nanometers to a few micrometers. According to one embodiment of the present invention, the internal concave surface of each reflector 135 is determined by at least the contour of the upper surface of each of the individual nanostructured LEDs. Part or all of the sides of the nanostructured LED also define the reflector part.

The nanostructured LED device 101 is considered to be a vertically stacked device having an LED array layer 180 containing a plurality of nanostructured LEDs 100 having a plurality of corresponding active regions 120 provided within the LED array layer 180. be able to. The plane parallel to the LED array layer 180 is the reflector layer 181 and is a plurality of reflectors with concave surfaces that are directed to the active region above one or a group and are configured to direct light through the LED array 180. Includes 135. According to one embodiment of the invention, the periodicity of the individual reflectors 135 of the reflector layer 181 is related to the periodicity of the individual nanostructured LEDs. The periodicity of the reflector layer 181 is related to the periodicity of the LED array layer 180 as a series of n or 1 / n, n = l, 2, 3 ... In another example, the reflector layer 181 has a random configuration or a periodicity that is not interrelated to the periodicity of the LED array layer 180.

The close proximity of the nanostructured array and the irregular shape of the reflectors provide the additional advantage that the layers can have multiple uses. As a heat conductor with higher efficiency than in traditional planar LEDs due to its proximity to the active region and the height of the relative surface junction region of the joint semiconductor and reflector material compared to the active region. Can function. Due to the closeness described above and the height of the relative surface junction area of the junction, it is also advantageous as an electrical contact with the LED array. Thus, this multipurpose layer can facilitate the design of devices for LED efficiency.

Nanostructured LED-based devices differ fundamentally from traditional planar LEDs in that light is emitted from a number of individual light sources rather than from a single continuous surface. The design of any array can be realized by lithographic means. The pitch and pattern of such LED arrays varies. In the present invention, in order to prevent light emission in a direction close to the plane of the array, it is preferable to configure the array with photonic crystal characteristics such as a triangular and hexagonal array so that the pitch is close to 1/2 of the wavelength of the emitted light. The use of this photonic crystal design in the active array is essentially different from the use of photonic crystal patterns located outside the active region and near the interface for extracting light from the semiconductor. This is because the proposed use of photonic crystal properties is aimed at aligning light from semiconductors towards mirrors and the final photo-extraction interface. For light from ultraviolet to infrared, it can be said that the pitch of such an array is in the range of approximately 0, 1-4 μm. The specific size of the individual LEDs is often limited by the choice of array pitch.

The nanostructured LEDs according to the present invention are briefly shown in FIGS. 1b to 1e. FIG. 1b shows a nanostructured LED composed of nanowires 110 and including a substrate 105, which is epitaxially grown from the substrate 105. Part of the nanowire 110 is surrounded by a volume element 115. The volume element 115 is preferably epitaxially connected to the nanowire 110. The pn junction, which is essential for the function of the diode, is formed in the volume element 115 or in the nanowire 110. Top contacts are provided on the volume element 115, eg, on the top or in a wrapping configuration on the peripheral outer surface. Even if the opposite ends of the nanostructured LED100 are connected, for example, via a substrate forming a common bottom contact, via a dedicated contact layer close to the substrate, or by a wrap contact at the bottom end of the nanowire 110. good. The wrap contact has an L-shape or a length to contact with the nanowire, which is determined by the thickness of the contact layer. Nanowire 110 typically has a diameter of about 50 nm to 500 nm and a volume element of 500 nm to 10 It has a diameter of about μm. Some of the length of nanowires that are not covered by volume elements varies from 10 nm to a few μm, depending on usage. Volume element lengths are typically and preferably 1-5 It is about μm. The volume element 115, or bulb, may have different shapes, and the combination of volume elements and nanowires so that the active regions are in different positions and shapes provides the recombination conditions required for photogeneration. Volume element 115 provides a higher degree of doping and electron carriers are injected into the nanowires. According to the present invention, nanostructured LEDs are designed to allow light to exit the device through a substrate 105 or, if the substrate is removed, a support structure. That is, referring to the figure, the light is directed downwards. According to the present invention, at least a portion of the generated light is a reflector located where the light exits the device from the nanowire, that is, near the end near the top end of the nanowire 110 and near the opposite end of the nanowire. Directed by 135. The illustrated reflector 135 has a cross section along the upper portion of the cut-out pyramid of the volume element 115, the shape of which can be made by known methods. As can be seen from the figure, the shape of the reflector follows the shape of the volume element 115, which represents a preferred embodiment from a manufacturing point of view. However, as mentioned above, many different shapes can be predicted and manufactured, and the shapes given by the illustrated shapes and volume elements should be considered as examples without limitation.

FIG. 1c is a diagram showing another design, in which the volume element 115 has a plurality of layers 116, 117 of the shell structure. The doping layer 117 provides the p or n region, and the well layer 116 contains the active region 120 in operation. In another example, wells can be made up of multiple sublayers. The structure may include other layers (not shown) to enhance doping properties, which can improve connectivity and the like. In this embodiment, the active region 120 is generally outside the nanowire 110. The reflector 135 surrounds the shell structure in this embodiment. The volume element / shell structure is shown here as pointed, which represents one possible, technically achievable practice. The reflector can be adhered to the volume element by the existing deposition technique so that it can have the desired intrinsic concave shape. The connections, dimensions, etc. described above are also appropriate for this embodiment. The nanostructured LED (100) of this embodiment outlined in FIGS. 1a-c can be described as a long structure with a pointed tip. In this case, it will be understood that pointed also includes the shape in which the outermost top is cut off, as shown in the figure. Nanostructured LEDs also have an elongated cylindrical portion with a vertical surface. The term vertical surface also includes the surface of an elongated cone.

A further embodiment is shown in Figure 1d. The nanowire 110 is surrounded by an overgrown quadrangular pyramid that forms the volume element 115. The active region 120 is in this case composed of nanowires or, if a shell structure is provided as shown, a volume element. The reflector 135 forms a corresponding pyramid shape, a triangle in the illustrated cross section, along the pyramid shape. In the illustrated example, a contact 137 is provided between the volume element 115 and the reflector 135.

Schematically shown in Figure 1e are nanostructured LEDs formed without the help of nanowires. A quadrangular pyramid 160 of the first semiconductor material is formed on the substrate 105, and then the semiconductor layers 161, 162 are grown to form a pn junction, which becomes an active region 120. Further, the reflector 135 according to the present invention can also be supplied to this type of structure.

The thin arrows in FIGS. 1a to 1e show the possible reflection paths of the light emitted from the active region and show the aiming effect on the substrate 105. ..

In all embodiments, a connecting means is required on top of the volume element forming the top contact. The top contact may be between the volume element and the reflector, in which case it is preferably a transparent or translucent material. Another example, which can be realized in other designs, is a transparent connecting layer 125 covering the volume element and a reflector 135 formed as a layer on top of the connecting layer 125, as shown in FIG. 1d. In a further different example, the reflector 135, for example in the form of a layer, acts as both a contact and a reflector.

The substrate 105 and a part of the upright structure may be covered with a thin film or a coating layer 107 as a material for filling the space surrounding the nanostructured LED as shown in FIG. 1b.

According to the embodiments shown in FIGS. 1a-e, the reflector 135 may be coupled to each nanostructured LED 100 as shown in FIG. 3a, which shows a device having a plurality of nanowires. The reflector covers only one nanostructured LED, but also contributes to aiming the light emitted from the other active regions 120, as indicated by the thin arrows that indicate the path of the light.

In another example, the reflector 135 is coupled with multiple nanostructured LEDs, as shown in Figure 3b. Looking towards the substrate in the direction of the nanowires, the reflector 135 covers the active regions 120 of the plurality of nanostructured LEDs. It is preferable to insert an interpolation material 136 having appropriate optical properties between the nanostructured LED and the reflector 135. The interpolation material 136 facilitates the formation of a concave reflector. The interpolation material must be transparent to the emitted wavelength of light. SiO deposited using methods such as sputtering, vapor deposition, or CVD.₂, Al₂O₃, Or Si₃N₄It may be an insulating layer of. In another example, it may be a semiconductor material deposited during epitaxial growth under conditions different from the growth of individual nanostructured LEDs. It may be made conductive so that it can be easily connected via the reflector.

In yet another example outlined in FIG. 3c, the cross section of the reflector 135 is sufficiently smaller than the diameter of the nanostructured LED, with the plurality of reflectors coupled to each nanostructured 100. To achieve this shape, the top surfaces of the individual nanostructured LEDs can be formed using etching or laser drawing methods.

According to one embodiment of the invention, nanostructured LED nanowires are used as waveguides that guide at least a portion of the light produced by the nanostructured LEDs in the direction provided by the upright nanowires. An ideal waveguide nanowire LED structure would include a high index core covered by one or more peripheral coatings, which has a lower index of refraction than the core. The structure is circularly symmetric or substantially circularly symmetric. Circular symmetric photogenic waveguides are well known in the application of fiber optics and can make many similarities in the field of rare earth-added fiber amplifiers and lasers. However, one of the differences is that the nanowire LED structures described can be considered electrically excited, whereas fiber amplifiers are photoexcited. One of the advantages of one well-known shape is the so-called numerical aperture NA, NA = (n).₁² --n₂²) And n₁And n₂Is the refractive index of the core and the coating, respectively. NA is determined by the angle of light captured by the waveguide. In the light generated in the core of the waveguide, the capture angle φ is n₁ --cos (φ) = n₂Can be obtained as. NA and the angle of captured light are important parameters in optimizing the new LED structure.

Typical values for Group 3 to Group 5 semiconductor core materials are refractive indexes in the range of 2.5 to 3.5. SiO with a refractive index of 1.4 ~ 2.0₂Or when combined with a glass-type coating material such as SiN, the capture angle can be as high as 65 degrees. A capture angle of 65 degrees means that up to 75% of the generated light can be captured by the structure and guided (in both directions).

In optimizing light extraction, it must be considered that NA changes along the nanowire structure in order to optimize light extraction from the structure. In general, it is ideal to have the highest NA when light production occurs farthest from the exit position. This allows the light captured and guided towards the outlet to be maximized. Conversely, the closer to the exit edge of the structure, the more the generated light radiates in any direction, and most of the radiated light hits the top of the structure and its sides and emits, so the NA can be reduced. .. Having a low NA at the top of the structure also minimizes light capture and downward guidance within the structure, which is not ideal unless the reflector is inserted at the bottom of the structure. Absent. Low NA can be obtained by covering the core of Group 3 to Group 5 nanowires with another Group 3 to Group 5 coating of a different composition with a slightly lower index of refraction. ..

According to an embodiment schematically shown in FIG. 4a, the nanowire 110 or part of the nanowire 110 directs at least a portion of the generated light in the normal direction provided by the extending direction of the nanowire. It is configured to form. The function of this nanowire is represented by a thin arrow in the figure. The pn junction results in the active region 120 being formed on the nanowires or in the vicinity of the nanowires, producing light. The position of the active region 120 in FIG. 4a is an example without limitation. The materials of the different parts of the nanostructured LED are such that the nanowires have good waveguide characteristics with respect to the surrounding material, that is, the refractive index of the material of the waveguide 116 is the refractive index of the peripheral material. Selected to be greater than. Nanowire 110 or waveguide 116 has a first index of refraction n_wThe material around the nanowires of the waveguide portion 116, typically the coating layer 107, has a second index of refraction n._cAnd the volume element has a third refractive index n_VEIf you have n_w&gt; n_cAnd n_w&gt; n_VEIs. Typical values for nanostructured LEDs are n_w 3, n_c 1.5, n_VE 3.

One or more coating layers may be provided for the waveguide 116. The first coating layer 112 was introduced to improve the surface properties of the nanowires, for example, when GaAs nanowires were used, it was shown that the addition of the GaInP coating layer 112 would improve the properties. I came. Further, for example, a coating layer such as an optical coating layer 113 may be introduced in a manner as established in the field of fiber optics, in particular to improve the light guide characteristics of the nanowire 110. The optical coating layer 113 typically has a refractive index between the index of refraction of the nanowires and the index of refraction of the peripheral material. Alternatively, the coating layer 113 has a gradually varying index of refraction, which has been shown to improve light transmission in certain cases. Refractive index n of nanowires when optical coating layer 113 is used_wDetermines the effective index of refraction of both the nanowires and the coating layer.

The ability to grow nanowires with a well-defined diameter depends on the wavelength of light produced by the nanostructured LED 100 according to one embodiment of the invention, as illustrated in the literature described above and below. It is used to at least optimize the light guide characteristics of the waveguide 116. As is well known, the recombination process, which is the basis of LED light generation, produces light in a narrow wavelength band depending on the characteristics of the material. In embodiments, the diameter of the nanowires 110 is chosen to better correspond to the wavelength of the light produced. Preferably, the dimensions of the nanowire 110 are such that a uniform optical resonator optimized for a particular wavelength of generated light is provided along the nanowire. The core nanowires must be wide enough to capture the light. As a rule of thumb, λ is the wavelength of the generated light, n_wIs the refractive index of nanowire 110, the diameter is λ / 2n_wMust be larger.

For nanostructured LEDs configured to produce light in the visible region, the diameter of the nanowire waveguide must preferably be greater than 80 nm in order for the nanowire to be an effective waveguide. For infrared and near infrared, diameters greater than 110 nm are sufficient. A preferred approximate upper limit for the diameter of nanowires is given by growth constraints and is around 500 nm. The length of the nanowire 110 is typically and preferably about 1-10 μm, which is an unnecessary length that can provide a sufficient volume for the active region 120 and at the same time cause internal absorption. is not it.

In the embodiment shown in FIG. 4a, the waveguide characteristics of the nanowire 110 and the aiming of the reflector 135 are combined to further enhance the extraction of light through the substrate 105. A significant portion of the light produced in the active region 120 is guided downward by nanowires. However, some of the light is radiated in various directions without being "captured" into the waveguide 116. Part of this light can be reflected by the reflector 135 towards the substrate through the waveguide 116 or other parts of the nanostructure.

In the embodiment outlined in FIG. 4b, the light is generated in the active region 120, which is essentially located outside the radial direction of the nanowire 110, i.e., the embodiment having the shell structure described with reference to FIG. 1b. Corresponds to. In this embodiment, the volume element is supplied with a coating layer 440 so that the volume element has a waveguide property. The reflector 135 above the volume element 115 reflects at least a portion of the upwardly emitted light downward.

In the embodiments described above, light is described as being radiated through the substrate 105 so as not to interfere with understanding. However, in LED devices with nanostructured LEDs, a notch 130 may be provided as shown in FIG. 4a to remove the substrate or facilitate light irradiation. Other layers, such as GaN buffer layers, to reinforce nanowire nuclei, or, for example, SiO₂The protective layer may be provided on the side of the nanowire. The substrate can be removed using wrapping and etching methods, which allow the substrate material to be cut or scraped off by etching. Alternatively, a lift-off process may be used to separate the epitaxially grown structure from the substrate.

The individual reflectors 135 in the nanostructured LED device 101 with the plurality of nanostructured LEDs 100 can conveniently be formed as a continuous reflective layer 535 covering the plurality of nanostructured LEDs 100, as outlined in FIG. 5a. .. The continuous reflective layer 535 should be regarded as a plurality of individual reflectors. As can be seen from the figure, the continuous reflection layer 535 in this embodiment covers most of the surface of each nanostructured LED. The continuous reflective layer 535 may fill the space between the individual nanostructured LEDs 100, as shown in the figure. In another example, for example SiO₂Filling layer 507 is provided for nanostructured LED devices and covers a portion of the height portion of the nanostructured LED. In this embodiment, the continuous reflective layer 535 is shown as a plurality of independent reflectors 135, which are essentially concave and cover the nanostructured LED, and essentially a flat surface 536, which covers the packed bed 507 connected thereto. be able to. This solution causes further reflection before the light is directed out, that is, between the connected planes and the substrate or buffer layer. This creates a contradiction between the height of the nanostructures and the further generation of light and the high absorption loss due to repeated reflections. This effect is due to the waveguide properties of the nanostructure, as light with a low angle to the stretch direction in the nanostructure is guided so that most of the first reflection of the light occurs in the recesses of the reflector. To limit.

Another realization example of the present invention is shown in FIG. 5c. Each nanostructured LED is provided with a transparent conductive layer 540 that covers the entire cylindrical surface of the nanostructured LED. Transparent conductive oxides (eg, ITO) deposited by sputtering deposition can be used to form such layers. In essence, the space between nanostructured LEDs is, for example, SiO.₂, Si₃N₄, Al₂O₃It is filled with a transparent insulating material 507 such as, and the tip of the LED is exposed. Finally, in practice, a reflector 535 with a plurality of independent reflectors 135 is formed. The reflector layer forms an electrical contact with the transparent contact layer 540 of each nanostructured LED. With this structure, it is possible to satisfactorily inject a current into the entire junction region while utilizing the optical characteristics of the reflector.

The choice of design for applying nanostructured LED devices depends on many parameters. The pyramidal structure described with reference to Figure 1d is optimal because the first reflection of the emitted light is already directed downwards at a high percentage with respect to light collimation and extraction and device efficiency. It can be predicted that it is close to something like that. However, the design requires high utilization of the surface area, which results in higher manufacturing costs than longer structures such as those shown in FIGS. 1b-d. The long pyramidal structure, as shown in Figure 13a, represents a functional compromise between these parameters.

The method of manufacturing nanostructured LEDs is to first grow nanowires according to the process described above. Then, a part of the nanowire is masked and the volume element is selectively regrown. This method is shown in FIG. Since the volume element grows both in the axial direction and in the radial direction, when the nanowire is partially masked, the nanowire is surrounded by the volume element. Suitable masking materials include, for example, silicon nitride, silicon oxide and the like.

Considering a system in which the growth of nanowires is partially emphasized by matter, such as VLS-grown nanowires, the ability to change radial and axial growth by changing growth conditions allows nanowires / higher-dimensional 3D sequences. The procedure (nanowire growth, mask formation, then selective growth) can be repeated to form. In a system where nanowire growth and selective growth are not distinguished by individual growth conditions, nanowires are first grown along their length, and then different types of 3D regions or volume elements are grown by different selective growth steps. It is good to let it.

The method for manufacturing a nanostructured LED device according to the present invention is

a) Determining the growth position on the substrate by lithography; b) Grow nanostructured LEDs from the substrate at a defined growth position; c) By depositing reflector material on at least the top of the nanostructured LEDs, each nanostructured LED forms an independent reflector; It has the basic steps of. The details of the method depend on the material, desired shape, and function of the nanostructured LED device. A manufacturing example is shown below.

The method forms the upper part of the nanostructured LED to determine the shape of the inner surface of the reflector overlying the nanostructured LED, which takes place after the process of growing the nanostructured LED and before depositing the reflector material. Including steps. Various etching or ablation methods can be used. Alternatively, a material may be added to the top of the nanostructure to determine the shape of the reflector.

A wide range of materials can be used for different parts of the structure, depending on the application of the nanostructured LED device, the availability of suitable manufacturing processes, the cost of the material, and so on. In addition, nanowire-based technology allows for flawless material combinations that would otherwise be impossible to combine. Group 3 to Group 5 semiconductors are particularly important because they have the property of facilitating high-speed, low-power electronic devices. Materials suitable for substrates are not limited to these, but Si, GaAs, GaP, GaP: Zn, GaAs, InAs, InP, GaN, Al.₂O₃, SiC, Ge, GaSb, ZnO, InSb ,, SOI (Silicon on Insulator), CdS, ZnSe, CdTe. Suitable materials for nanowires 110 and volume elements 115 are, but are not limited to, GaAs (p), InAs, Ge, ZnO, InN, GaInN, GaN AlGaInN, BN, InP, InAsP, GaInP, InGaP: Si. , InGaP: Zn, GaInAs, AlInP, GaAlInP, GaAlInAsP, GaInSb, InSb, Si included. For example, possible donor dopants for GaP are Si, Sn, Te, Se, S and the like, and acceptor dopants for the same material are Zn, Fe, Mg, Be, Cd and the like. Since the nanowire technology has made it possible to use nitrides such as GaN, InN and AlN, it is possible to facilitate the production of LEDs that emit light in a wavelength region that could not be easily achieved by conventional technology. .. Other commercially important combinations include, but are not limited to, GaAs, GaInP, GaAlInP, and GaP systems. Typical doping level is 10¹⁸From 10²⁰Is the range of. Those skilled in the art will appreciate that these and other materials are familiar and that other materials and combinations of materials are possible.

The suitability of low resistance contact materials depends on the material being deposited, but with metals, alloys, and Al, Al-Si, TiSi.₂, TiN, W, MoSi₂, PtSi, CoSi₂, WSi₂, In, AuGa, AuSb, AuGe, PdGe, Ti / Pt / Au, Ti / Al / Ti / Au, Pd / Au, non-metal compounds such as ITO (InSnO), and, for example, combinations of metal and ITO. Can be used.

The manufacturing method according to the present invention for manufacturing a light emitting pn diode / array having an active nanowire region formed of GaAs and InGaP, shown in FIG. 6, includes the following steps: 1. By lithography, the range of partial catalyst is limited on the p + type GaP substrate 1305. 2. Nanowire 1310 is grown from partial catalyst 1331. The growth parameters are adjusted according to the growth of the catalytic wire. 3. Radially grow a thin film InGaP concentrated layer 1312 around the nanowires (coating layer). 4.SiO₂Is deposited as mask material 1332. 5. Back-etch the mask 1332 to open the top of the nanowires. 6. Selectively grow n + -type InGaP volume element 1315. The growth parameters are adjusted to grow in the radial direction. 7. A reflector is formed on the volume element by depositing a reflective material on at least a part of the volume element 615.

The growth process can be modified in a known manner, for example, so that the nanowires contain a heterostructure and provide a reflective layer and the like. The shaft 113 used in some embodiments first grows thin nanowires (step 2), deposits a reflective layer or a selective growth mask covering the underside, and then increases the thickness of the nanowires. Provided by growing the coating layer or nanowires in the radial direction. ..

A further example of realizing a nanostructured LED used in the nanostructured LED device according to the present invention is a GaAs nanowire epitaxially grown on a GaP and Si substrate. LED functionality has been established on both types of substrates. The structure is evaluated in terms of temperature-dependent photoluminescence, electroluminescence, and radiation pattern.

LED devices, according to realizations, include Group 3-5 light emitting nanowire diode arrays grown and grouped on Si. Each device is built around a GaAs nanowire core linearly grown on GaP or Si. Each diode portion acts as an active region in these separate nano-sized pin emission structures.

The LED device 701 shown in FIG. 7 includes a pin diode structure 700. The substrate 705 is a device integration because it functions as a common p-layer. Each nanostructured LED700 structure has a nanowire 710, a coating 730 surrounding at least a portion of the nanowire, a cap or bulb 715, and a top contact. The order of p-doping, n-doping, and intrinsic semiconductor material depends on the substrate material. The structures on GaP are p-GaP (board) 705, i-GaP711 / i-GaAs (nanowire) 710, i-InGaP (coating) 730, and n-InGaP (valve) 715. The structures on Si are p-Si (base) 705, i-GaP / i-GaAs (nanowire) 710, i-InGaP (coating) 730 / n-InGaP (valve) 715. The i-GaP711 (nanowire) at the base of the nanowire, with a thickness of about 60 nm for both devices, serves the dual purpose of the nucleation segment: growth quality and improved electron barrier.

The outline of the manufacturing process is described below. THMa metal organic source and TMIn as precursor gas AsH₃, PH₃, And Si₂H₆Used with. Two growth steps are applied. First, 2 μm long GaAs / GaP nanowires were optionally deposited, nanometer-sized, 1 / μm in diameter at 60 nm.²P-GaP (111) B (p 10) by particle-assisted growth using Au aerosol having the molecular concentration of¹⁸cm^-3) And Si (111) (p 10¹⁵cm^-3) Grow on the substrate. The nanowires are surrounded by a 40 nm-thick radial InGaP coating layer that is nominally lattice-matched to GaAs. After this step, samples are unloaded for photoluminescence or subsequent nanoLED production. 80 nm thick SiO₂Are deposited on a row of samples to make an LED. SiO₂Is back-etched to the side of the nanowire, about lμm, to cover only the substrate surface. The sample is then reloaded into the MOVPE reactor and the radial Si-doped InGaP layer is selectively grown on top of the GaAs / InGaP core structure. The LEDs are 200 x 200 μm with a thickness of 150-300 nm, each covering approximately 40,000 independent nanostructured LEDs.²Completely covered by square Ni / Ge / Au contacts. The p-type contact is made of conductive Ag paste on the back side of the substrate. As other contact means, for example, the use of transparent contacts is known in the art and can be easily adapted to the methods and devices of the present invention. A scanning electron microscope (SEM) image of the structure is shown in Figure 8a.

An important difference between Si and GaP devices is the heterostructure sequence at the base of the nanowires, on which there are p-GaP (base) / i-GaP layer (nanowire) / i-GaAs layer (nanowire). On the other hand, there are p-Si (base) / i-GaP (nanowire) / i-GaAs (nanowire) on the Si substrate. It should also be predictable that both hole injection conditions and internal resistance will differ significantly between the two structures.

FIG. 9 shows the nanowire structure after the first MOVPE step. The figure shows a GaAs nanowire with a thin film InGaP coating layer, a GaP nucleation segment at the base of the nanowire, with Au-based seed particles still attached to the tip. Such structures are also transferred to the neutral substrate for PL characterization. As shown in FIG. 9, the yield is basically 100% for both the GaP substrate and the Si substrate. Manufacture of nanostructured LEDs on Si is where nanowires are evenly arranged in the (111) direction perpendicular to the substrate, and basically any nanowire grows in three tilted (111) directions extending from the substrate. It will be refined to the point where it does not. This is compared with the prior art method of group 3-5 nanowire growth on Si (111). The growth of well-aligned Group 3-5 nanowires in a predetermined array structure on a Si substrate is for large-scale manufacturing of optical devices and most other applications, as shown in Figure 9. , Indispensable.

LED function can be demonstrated by photoluminescence (PL) measurement. The measurements shown here were performed at room temperature and a temperature of 10K. The results are shown in the graphs of FIGS. 10a to 10c and 8b. Laser emission at 473 nm was used as the excitation source. PL was collected by light microscopy, spectroscopically spectroscopic, and detected by a liquid nitrogen cooled CCD camera.

To examine PL from the nanowires unaffected by the substrate, the nanowires were broken, the nanowires moved from the grown substrate and deposited on the patterned Au surface. Nanowires can be examined individually in this way. As shown in FIG. 10a, the PL spectrum obtained at 10K from the nanowires grown in this way is obtained from the nanowires grown on the Si substrate, the nanowires grown from the Si substrate (Si), and the GaP substrate (GaP). It was similar to the grown nanowires. The dashed line is the spectrum from the (many) nanowires still standing on the substrate. The spectra from the individual nanowires showed large differences, and the nanowires grown from the GaP substrate were more systematic. The average PL concentration of nanowires grown from Si was about 1/20 that of the corresponding nanowires grown from GaP. This is in good agreement with the electroluminescence found in Si LEDs, which is 10 to 30 times lower than in GaP LEDs. At room temperature, the spectra were wide and featureless, and the spectral differences between the nanowires from the two samples were very small.

Both the LEDs on GaP and the LEDs on Si showed electroluminescence (EL) when forward biased, as shown in Figure Ta-b. The peaks of the light spectrum are in good agreement with the bandgap energy of GaAs.

The photopower / photocurrent dependencies are shown in FIGS. 11a and 11b for Si-group (Si) and GaP-group (GaP) LEDs. The LEDs on the GaP light up at half the current load (20 mA) of Si (40 mA), and at 60 mA the power output is about 30 times higher on the GaP board. However, at 100 mA, the power ratio was reduced to 10 times that of Si-based LEDs. The peaks of the EL spectrum at 80 mA load are shown for both devices. The Si LED peaks show a tail with some redshift and a possible special peak near 1.35 eV compared to the GaP substrate device. The peak shift can be explained by different In and Ga scattering on GaP and Si, leading to different InGaP compositions. By pushing the device and increasing the current, you can see the peak power at about 14 OmA on the GaP device. This may not be visible in Si devices and may indicate that non-radioactive recombination or competing leakage mechanisms dominate EL at these current levels.

Group 3 nitride nanowires such as GaN and LED devices made on nanostructures are of high commercial importance because they can generate light with wavelengths that cannot be obtained by combining other materials. .. As a further example, how to produce GaN nanostructures on selective region growth on GaN epitaxial films, sapphires, SiC or Si, and even self-supporting GaN will be described. On the first board, SiN_xA layer (thickness 30 nm) is deposited by PECVD. In subsequent steps, an array of dot-patterned GaN apertures (approximately 100 nm in diameter) is generated by epitaxial beam lithography (EBL) and reactive ion etching (RIE). The opening pitch should be between 1.0 and 3.2 μm. Samples thus treated are then inserted into a horizontal MOCVD chamber to grow GaN nanowires and LEDs with GaN / InGaN nanostructures. As shown in the SEM images of FIGS. 12a-c and 13a-b, various shapes can be formed. A pyramidal structure can be formed as shown in FIGS. 12a and 12b. FIGS. 12c and 13b show that nanowires with pyramidal-shaped ends can be formed, which is advantageous for forming the efficient reflectors of the present invention. The vertical sidewalls are usually 6 (1101) planes. Pyramids are usually ranged by six equivalent (1101) planes, but as shown in Figure 13a, they form a higher index of refraction plane and another refraction plane with one nanostructured LED. Can be housed inside.

Although the present invention has been described in the context of what is considered most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but rather is within the scope of the appended claims. It will be understood that it is intended to include various changes and equivalent configurations.