Semiconductor light emitting device

0001The present invention relates to a radiation-emitting semiconductor component according to the preamble of claim 1.

0002Such radiation-emitting semiconductor components can be implemented, for example, as vertically emitting semiconductor components. The vertical emission direction generally runs essentially perpendicular to a lateral main direction of extent of the semiconductor layer sequence, in particular its surface. In such components, the first mirror is often designed as a Bragg mirror for the directed reflection of radiation generated in the active zone.

0003A Bragg mirror usually contains several pairs of semiconductor layers with a respective layer thickness of approximately λ / (4n), where λ indicates the wavelength of the radiation generated in the active zone and n the refractive index of the respective semiconductor layer.

0004The Bragg mirror is usually highly reflective, for example with a reflectivity of 99% or more, which generally requires a comparatively high number of semiconductor layer pairs, for example 30 or more, which subsequently lead to a significant thickness of the Bragg mirror and thus of the semiconductor component.

0005Such a component can be designed as a laser component with a vertical emission direction, which is provided for generating coherent radiation by means of an internal resonator (VCSEL: Vertical Cavity Surface Emitting Laser) or an external resonator (VECSEL: Vertical External Cavity Surface Emitting Laser). In the case of a VCSEL, a second mirror for the internal resonator is generally monolithically integrated together with the first mirror in the semiconductor layer sequence. For a VECSEL, the semiconductor layer sequence is followed by an external mirror for the optical resonator.

0006Furthermore, the heat loss generated in the operation of such a semiconductor component in the active zone can have a disadvantageous effect on the function of the component. Good heat dissipation from the component is therefore desirable. Due to the numerous interfaces in a highly reflective Bragg mirror, heat dissipation from the active zone is hampered. This is particularly the case when the materials of the Bragg mirror have a relatively low thermal conductivity anyway and the heat dissipation is further impaired by the large number of interfaces.

0007Efficient electrical contacting of the component through the Bragg mirror is also made more difficult due to its significant thickness.

0008The object of the present invention is to provide an improved radiation-emitting semiconductor component of the type mentioned at the outset, which in particular can be made small and compact and with increased efficiency.

0009This object is achieved by a radiation-emitting semiconductor component with the features of claim 1. Advantageous developments of the invention are the subject of the dependent claims.

0010A radiation-emitting semiconductor component according to the present invention has a semiconductor layer sequence with an active zone provided for generating radiation and a first mirror arranged downstream of the active zone, the first mirror comprising a metal layer and an intermediate layer made of a radiation-permeable layer arranged on the side of the metal layer facing the active zone and comprises electrically conductive material, wherein the radiation-emitting semiconductor component is provided for operation with an optical resonator and for generating incoherent radiation as RCLED or for operation with an external optical resonator and for generating coherent radiation as VECSEL.

0011It should be noted that a semiconductor component which is designed to generate predominantly incoherent or predominantly coherent radiation can also be regarded as encompassed by the invention.

0012Such a first mirror with the metal layer and the intermediate layer has the advantage of improved heat dissipation from the radiation-emitting semiconductor component compared to a pure Bragg mirror. A Bragg mirror with the same reflectivity typically has more than 20 pairs of semiconductor layers. Such a high number of semiconductor layers, however, can hinder the removal of heat from the active zone due to the large number of interfaces and thus shorten the life of the component.

0013The number of interfaces or pairs of semiconductor layers in the invention can advantageously be kept low because of the high reflectivity of the metal layer, which advantageously improves the heat dissipation. Furthermore, metals usually have a higher thermal conductivity than the materials of a Bragg mirror, which further improves the heat dissipation. This is for the efficiency and the service life of components with high power loss or Heat development, especially a VECSEL, is particularly advantageous.

0014Another advantage of the invention is the low penetration depth of the radiation generated in the active zone into the metal layer. The depth of penetration into a Bragg mirror with the same reflectivity is significantly greater than the depth of penetration into a metal layer, which is typically less than a quarter of the wavelength, because of the large number of semiconductor layer pairs of the thickness λ / (4n) involved in the reflection. The depth of penetration into the Bragg mirror is largely determined by the thickness of the Bragg mirror. The penetration depth into the Bragg mirror generally grows initially with the number of semiconductor layer pairs of the Bragg mirror and can converge to a value which is determined by a difference in the refractive indices of the materials used for the individual semiconductor layers of the semiconductor layer pairs. Seen from the active zone, the Bragg mirror thus acts as a virtual mirror of the same reflectivity and negligible extent, which is further away from the active zone by the penetration depth compared to the position of a first layer of the Bragg mirror arranged adjacent to the active zone.

0015Because of the small penetration depth into the metal layer, the active zone in the invention can advantageously be positioned closer to a corresponding virtual first mirror than in the case of a pure Bragg mirror, as a result of which the efficiency of the radiation-emitting semiconductor component can be increased. This applies in particular to an RCLED (Resonant Cavity Light Emitting Diode), the efficiency of which depends largely on the arrangement or the distance of the active zone to the virtual first mirror is influenced. An arrangement at a well-defined distance close to the first mirror is of particular advantage for an RCLED. Forming the first mirror with a metal layer increases the degrees of freedom in the choice of distance from the virtual first mirror and thus contributes to increasing the efficiency of the component.

0016In contrast to lasers, the optical resonator of an RCLED does not serve to amplify individual modes by means of stimulated emission, but rather the spontaneously emitted radiation is directed in one direction of emission. Compared to a radiation coupled out from a conventional LED without a resonator, the radiation coupled out from the resonator of an RCLED can have an increased radiation power. An RCLED is usually designed as a surface-emitting component with a vertical emission direction.

0017It should be noted that in the context of the invention, a metal layer can also be regarded as a metal layer, which in particular also includes a layer which contains an alloy. However, a layer made of metal is particularly suitable.

0018The low directional dependence of the reflectivity of the metal layer compared to a pure Bragg mirror can also advantageously influence the efficiency of the radiation-emitting semiconductor component. The reflectivity of Bragg mirrors is usually greatest in the area around their surface normal and decreases relatively strongly with increasing angle of incidence to this normal. In contrast, the reflectivity of metal layers is approximately constant over a wide angular range, so that radiation incident at a large angle is still highly reflected and can be coupled out of the component. By means of the metal layer, radiation incident on the metal layer can also be reliably reflected, in particular at comparatively large angles. Even radiation components of this type with large angles of incidence can thus be directed more easily in the emission direction.

0019The semiconductor layer sequence, in particular the active zone, preferably contains at least one III-V semiconductor material, for example a material from the material systems In_xGa_yAl_1-xyPin code_xGa_yAl_1-xyN or In_xGa_yAl_1-xyAs, each with 0≤x≤1, 0≤y≤1 and x + y≤1. III-V semiconductor materials are characterized by their advantageous high quantum efficiency and are used to generate radiation from ultraviolet (e.g. In_xGa_yAl_1-xyN) over the visible (e.g. In_xGa_yAl_1-xyN or In_xGa_yAl_1-xyP) into the infrared spectral range (e.g. In_xGa_yAl_1-xyAs) particularly suitable. Furthermore, the radiation generated in the active zone preferably has a wavelength in the visible, in particular red, spectral range. The material system is In for this spectral range_xGa_yAl_1-xyP particularly suitable.

0020In a preferred embodiment of the invention, the active zone comprises a single or multiple heterostructure, in particular a double heterostructure, or a quantum well structure, in particular a multiple quantum well structure. Such structures allow an advantageously high internal quantum efficiency of the semiconductor component to be achieved.

0021In the context of the application, the term quantum well structure encompasses any structure in which charge carriers experience a quantization of their energy states through confinement. In particular, the term quantum well structure contains no information about the dimensionality of the quantization. It includes quantum wells, quantum wires and quantum dots and any combination of these structures.

0022The metal layer of the first mirror is preferably electrically conductively connected to the semiconductor layer sequence via the intermediate layer. In addition to the reflection of radiation generated in the active zone, such a metal layer can also be involved in the electrical contacting of the radiation-emitting semiconductor component and advantageously brings about a homogeneous lateral energization of the active zone. The metal layer particularly preferably contains Au, Ag, Al, Pt or an alloy with at least one of these materials. Au has a particularly high reflectivity in the red and A1 or Ag also in the green and blue spectral range.

0023Furthermore, the metal layer can be arranged on a heat sink, as a result of which the heat dissipation from the component or the active zone is improved.

0024In the invention, the intermediate layer is preferably designed to be electrically conductive and is further connected to the semiconductor layer sequence in an electrically conductive manner. The material of the intermediate layer advantageously has a higher adhesion to the semiconductor layer sequence than the material of the metal layer and has an advantageous effect on the electrical contact between the metal layer and the semiconductor layer sequence.

0025The intermediate layer particularly preferably contains a radiation-permeable conductive oxide (transparent conducting oxide, in short: TCO), in particular a metal oxide, for example a zinc oxide such as ZnO, a tin oxide such as SnO, a titanium oxide such as TiO, an indium oxide such as InO, or a Indium tin oxide, such as ITO. Such materials are characterized by a high conductivity, in particular in the lateral direction, and high radiation transmission over a wide wavelength range. In addition, Zn can act as a dopant, in particular an acceptor, with respect to III-V semiconductors and thus improve the electrical contact with the semiconductor layer sequence, in particular a p-type semiconductor layer of the layer sequence adjacent to the intermediate layer. In this way, the formation of a barrier-free or ohmic electrical contact to the semiconductor layer sequence can be facilitated, for example by diffusion of the dopant into the semiconductor layer sequence. The same applies to Sn as a donor with respect to an adjacent n-conducting layer of the semiconductor layer sequence. The intermediate layer can be suitably doped to increase its conductivity, for example with Al in the case of a zinc oxide or Sb in the case of a tin oxide.

0026With such first mirrors, high reflectivities of over 90% can be achieved with good electrical contact properties and an advantageously small thickness of the mirror.

0027In a preferred embodiment, the intermediate layer is at least partially designed such that a radiation component reflected on the metal layer and a radiation component reflected on the side of the intermediate layer facing the semiconductor layer sequence are structurally superimposed.

0028This dimensioning of the intermediate layer increases the efficiency of the component, since destructive interferences, which can occur with an arbitrarily dimensioned intermediate layer, are avoided. This formation of the intermediate layer is all the more advantageous the higher the refractive index difference between the material of the intermediate layer and the material adjoining on the side of the semiconductor layer sequence, since the proportion of radiation reflected on this side of the intermediate layer increases with an increasing refractive index difference.

0029The structural superposition of the radiation components mentioned above can be achieved, for example, by forming the intermediate layer with a suitable thickness.

0030In a preferred embodiment, the intermediate layer is at least partially, preferably completely, designed such that its thickness, apart from integral multiples of half the wavelength, is less than a quarter of the wavelength of the radiation generated in the active zone in the material of the intermediate layer. The following therefore applies to the thickness D of the intermediate layer<maths id="math0001" num="(1)"><math display="block"><mrow><mi mathvariant="normal">D</mi><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>4</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>+</mo><mi mathvariant="normal">k</mi><mo>⋅</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>2</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>−</mo><mi mathvariant="normal">l</mi><mo>,</mo></mrow></math><img file="EP1662584A2_D0001.tif" /></maths>where λ is the wavelength of the radiation generated in the active zone in a vacuum, n_e.g. is the refractive index of the intermediate layer, k is a natural number (k = 0,1,2, ...) and 1 is a finite, non-zero residual length.

0031The remaining length 1 is preferably less than a quarter of the wavelength λ '(λ / n_e.g.), preferably less than one eighth of the wavelength λ ', where λ' denotes the wavelength of the radiation generated in the active zone (2) in the intermediate layer (3).

0032To form a structural interference, the thickness of the intermediate layer is at least partially selected so that the radiation reflected on the metal layer and on the side of the intermediate layer facing the semiconductor layer sequence have a phase difference of approximately zero or even multiples of π. Possible phase jumps due to reflection, such as on the metal layer and on the side of the intermediate layer facing the semiconductor layer sequence, must be taken into account.

0033If the refractive index is n_e.g. of the intermediate layer is smaller than that of the material adjoining on the side of the semiconductor layer sequence, the thickness D of the intermediate layer preferably at least approximately fulfills the relationship for a structural superposition of radiation incident on the intermediate layer <maths id="math0002" num="(2)"><math display="block"><mrow><mi mathvariant="normal">D</mi><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>4</mn><mi mathvariant="normal">π</mi><mo>⋅</mo><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>⋅</mo><mrow><mo>(</mo><mrow><mn>2</mn><mi mathvariant="normal">k</mi><mi mathvariant="normal">π</mi><mo>+</mo><mi mathvariant="normal">Φ</mi></mrow><mo>)</mo></mrow><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>2</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>⋅</mo><mrow><mo>(</mo><mrow><mi mathvariant="normal">k</mi><mo>+</mo><mfrac><mi mathvariant="normal">Φ</mi><mrow><mn>2</mn><mi mathvariant="normal">π</mi></mrow></mfrac></mrow><mo>)</mo></mrow><mo>.</mo></mrow></math><img file="EP1662584A2_D0002.tif" /></maths>

0034Here λ is again the wavelength of the radiation generated in the active zone in a vacuum, k (k = 0,1,2, ...) is a natural number and Φ is the phase jump due to reflection on the metal layer. The factor λ / (4π · n_e.g.) corresponds to the phase contribution 2D · (2π · n_e.g.) / λ, which results from the double passage of radiation reflected on the metal layer through the intermediate layer of thickness D.

0035If the refractive index is n_e.g. the intermediate layer is larger than that of the material adjacent on the side of the semiconductor layer sequence, the term 2kπ has to be replaced by (2k + 1) π due to the additional phase shift of π from the reflection on an optically denser medium, so that in this case for the thickness D the intermediate layer preferably at least approximately applies: <maths id="math0003" num="(2')"><math display="block"><mrow><mi mathvariant="normal">D</mi><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>4</mn><mi mathvariant="normal">π</mi><mo>⋅</mo><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>⋅</mo><mrow><mo>(</mo><mrow><mrow><mo>(</mo><mrow><mn>2</mn><mi mathvariant="normal">k</mi><mo>+</mo><mn>1</mn></mrow><mo>)</mo></mrow><mi mathvariant="normal">π</mi><mo>+</mo><mi mathvariant="normal">Φ</mi></mrow><mo>)</mo></mrow><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>2</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>⋅</mo><mrow><mo>(</mo><mrow><mi mathvariant="normal">k</mi><mo>+</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mo>+</mo><mfrac><mi mathvariant="normal">Φ</mi><mrow><mn>2</mn><mi mathvariant="normal">π</mi></mrow></mfrac></mrow><mo>)</mo></mrow></mrow></math><img file="EP1662584A2_D0003.tif" /></maths>

0036An ideal metal layer has an unlimited conductivity, so that when an electromagnetic wave is reflected, a phase jump of π results. According to equation (2), the thickness is D_id the intermediate layer for such an ideal metal layer <maths id="math0004" num="(3)"><math display="block"><mrow><msub><mi mathvariant="normal">D</mi><mrow><mi mathvariant="normal">id</mi></mrow></msub><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>4</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>+</mo><mi mathvariant="normal">k</mi><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>2</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>.</mo></mrow></math><img file="EP1662584A2_D0004.tif" /></maths>

0037A real metal, on the other hand, has only finite conductivity and the phase jump due to reflection on the metal layer results, for example, from the Fresnel formulas using the complex refractive index of the real metal. The thickness of the intermediate layer D_re on a real metal layer results from (2) <maths id="math0005" num="(4)"><math display="block"><mrow><msub><mi mathvariant="normal">D</mi><mrow><mi mathvariant="normal">re</mi></mrow></msub><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>2</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>⋅</mo><mrow><mo>(</mo><mrow><mi mathvariant="normal">k</mi><mo>+</mo><mfrac><mrow><msub><mi mathvariant="normal">Φ</mi><mrow><mi mathvariant="normal">re</mi></mrow></msub></mrow><mrow><mn>2</mn><mi mathvariant="normal">π</mi></mrow></mfrac></mrow><mo>)</mo></mrow><mo>.</mo></mrow></math><img file="EP1662584A2_D0005.tif" /></maths>

0038The thickness D_re the intermediate layer for a real metal layer preferably deviates by approximately <maths id="math0006" num="(5)"><math display="block"><mrow><msub><mi mathvariant="normal">d</mi><mi mathvariant="normal">M</mi></msub><mo>=</mo><msub><mi mathvariant="normal">D</mi><mrow><mi mathvariant="normal">id</mi></mrow></msub><mo>−</mo><msub><mi mathvariant="normal">D</mi><mrow><mi mathvariant="normal">re</mi></mrow></msub><mo>=</mo><mfrac><mi mathvariant="normal">λ</mi><mrow><mn>2</mn><msub><mi mathvariant="normal">n</mi><mi mathvariant="normal">e.g.</mi></msub></mrow></mfrac><mo>⋅</mo><mfrac><mrow><mrow><mo>(</mo><mrow><mi mathvariant="normal">π</mi><mo>−</mo><msub><mi mathvariant="normal">Φ</mi><mrow><mi mathvariant="normal">re</mi></mrow></msub></mrow><mo>)</mo></mrow></mrow><mrow><mn>2</mn><mi mathvariant="normal">π</mi></mrow></mfrac></mrow></math><img file="EP1662584A2_D0006.tif" /></maths> of thickness D_id on an ideally conductive metal layer so that constructive interference is achieved.

0039Since the phase that experiences radiation incident on a real metal layer upon reflection is generally positive, d_M mostly positive.

0040The size d_M can be viewed within the scope of the invention as the depth of penetration into the metal layer, which determines or co-determines the position of the corresponding virtual first mirror. For real metals, this penetration depth is usually less than a quarter wavelength, often less than an eighth wavelength, of the radiation generated in the active zone in the intermediate layer.

0041Furthermore, the depth of penetration d_M and the remaining length 1 is preferably 20 nm or less, particularly preferably 10 nm or less. In particular, the remaining length and the depth of penetration can also differ from one another or match by less than 5 nm.

0042The phase Φ_reAccordingly, the radiation reflected on the real metal layer can be compensated for by a corresponding thickness of the intermediate layer in such a way that the radiation components reflected on the metal layer and on the side of the intermediate layer facing the semiconductor layer sequence have a phase difference which is at least approximately equal to zero or an integer Multiples of n. The phase difference of zero is made possible in that the phase due to reflection on the metal layer and the phase caused by the passage of the radiation through the intermediate layer can have opposite signs. This applies in particular to positive phases Φ or Φ_re by reflection on the metal layer.

0043In an advantageous development of the intermediate layer, its thickness D is given by equation (1) with k = 0 and the remaining length 1 is determined according to one of the above requirements. The thickness D of the intermediate layer thus deviates by the remaining length 1 from λ / (4n_e.g.).

0044This has the advantage that the thickness of the intermediate layer is easier to control when it is applied, since with a small layer thickness of the intermediate layer any irregularities in the thickness are easier to detect and thus to be checked than with layer thicknesses with larger k values ​​and the same remaining lengths 1. Furthermore the thickness of the first mirror is thereby advantageously kept small.

0045In the invention, the optical resonator can be designed as an internal or external resonator.

0046The resonator is preferably formed by the first and a second mirror, which is arranged on the side of the active zone facing away from the first mirror. The reflectivity of the second mirror is particularly preferably smaller than that of the first mirror, with further preference the second mirror forming a coupling-out mirror of the radiation-emitting semiconductor component. An effective resonator length of the semiconductor component is determined by the distance between the first and the second virtual mirror. A small effective resonator length is particularly advantageous for an RCLED.

0047In the invention, an internal resonator can be formed, for example, with a Bragg mirror as the second mirror, which is preferably formed as part of the semiconductor layer sequence and is integrated therein.

0048In the invention, an external resonator can be formed, for example, with a dielectric mirror as the second mirror, which is arranged at a distance from the semiconductor layer sequence.

0049In the case of laser components such as VCSELs or VECSELs, the reflectivity of the coupling-out mirror, which is necessary for laser work, is usually greater than 98%. Remaining, non-decoupling resonator mirrors often require even higher reflectivities to ensure that laser activity is achieved.

0050The reflectivity of the coupling-out mirror is usually lower in the case of an RCLED, which preferably has an internal resonator, than in the case of a laser, since an RCLED is designed for a high coupling-out efficiency that would be unnecessarily reduced by a highly reflective coupling-out mirror, as is customary or necessary in the case of lasers. Typical reflectivities of the coupling-out mirror are 90% or less, preferably 80% or less, particularly preferably 70% or less. A reflectivity of 60% or less can also be suitable.

0051In a further preferred embodiment of the invention, in addition to the metal and the intermediate layer, the first mirror comprises a Bragg mirror which is arranged on the side of the intermediate layer facing the active zone, preferably between the intermediate layer and the active zone. In particular, the Bragg mirror can be integrated in the semiconductor layer sequence.

0052This Bragg mirror preferably contains less than 20, preferably less than 6 and particularly preferably less than 4, pairs of semiconductor layers. Such an additional Bragg mirror advantageously increases the reflectivity of the first mirror.

0053The combination of metal layer, intermediate layer and additional Bragg mirror makes it possible to form a first mirror which, compared to a Bragg mirror of the same reflectivity formed only by pairs of semiconductor layers, contains a substantially smaller number of pairs of semiconductor layers and has a smaller thickness. Such a thin, highly reflecting mirror is of particular advantage for directional emission in an efficient (RC) LED. With VCSEL or VECSEL, for example, a pure Bragg mirror usually requires more than 20 pairs of semiconductor layers in order to achieve a reflectivity of more than 98% that is often necessary.

0054In contrast, the number of semiconductor layer pairs can be kept lower within the scope of the invention. A reflectivity of 98%, for example, can be achieved by an additional Bragg mirror with 3 pairs of semiconductor layers in connection with the metal layer and the intermediate layer.

0055Such a first mirror is particularly advantageous if the materials available for a monolithically integrable Bragg mirror have only comparatively small differences in refractive index and a correspondingly high number of semiconductor layer pairs of this difference in refractive index would be necessary to achieve a high reflectivity.

0056The depth of penetration into the first mirror and the thickness of the first mirror can thus advantageously be reduced with high reflectivity of the first mirror. This can have a positive effect on the efficiency of the radiation-emitting semiconductor component, in particular an RCLED.

0057The comparatively small number of semiconductor layer pairs of an additional Bragg mirror furthermore not only leads to an advantageously improved heat dissipation, but also to shorter manufacturing times, in particular epitaxy times, for the semiconductor layer sequence, which can include the Bragg mirror of the first mirror.

0058In the invention, the Bragg mirror or mirrors preferably contain a III-V semiconductor material suitable for the radiation generated in the active zone, particularly preferably In_xGa_yAl_1-xyPin code_xGa_yAl_1-xyN or In_xGa_yAl_1-xyAs, each with 0≤x≤1, 0≤y≤1 and x + y≤1.

0059In a preferred embodiment of the invention, the semiconductor layer sequence with the active zone is produced by epitaxial growth on a growth substrate. Subsequently, the intermediate layer and then the metal layer, for example in each case by sputter deposition or vapor deposition, is applied to the side of the semiconductor layer sequence facing away from the growth substrate. The semiconductor layer sequence is subsequently connected to a suitable carrier on its side facing away from the growth substrate. The connection is preferably made electrically conductive and / or takes place by means of the metal layer. The metal layer can be bonded to the carrier, for example by means of eutectic bonding with suitable metal layers, soldered or glued, for example by means of an adhesive, preferably of an electrically conductive design. A connection layer which forms during the connection is preferably arranged between the metal layer and the carrier. The growth substrate is subsequently detached and the composite of carrier, metal layer, intermediate layer and semiconductor layer sequence is separated into components, each comprising a part of the semiconductor layer sequence (mesa), using a suitable separation process - for example dry chemical mesa etching and subsequent sawing.

0060Such radiation-emitting semiconductor components produced by detaching the growth substrate and fastening them on a carrier are also referred to as thin-film components.

0061The carrier can also be designed as a heat sink, in particular a metal-containing one, which improves the heat dissipation from the active zone.

0062In an advantageous development of the invention, a contact structure for electrical contacting of the radiation-emitting semiconductor component, preferably in the form of a contact metallization, is arranged on the side of the active zone facing away from the first mirror. An electrical insulation layer is preferably arranged under an area of ​​the active zone, in particular on its side facing away from the contact structure, which is covered by the contact structure, in particular in a component area downstream of the contact structure in the vertical direction. The insulation layer is particularly preferably arranged in a recess or cutout of the first mirror, which the latter may have in the region which is covered by the contact structure.

0063Such an insulation layer advantageously reduces the injection of current into the area of ​​the active zone which is covered by the contact structure. As a result, a low radiation power is generated in this area of ​​the active zone compared to the other areas. Radiation can thus only be absorbed to a lesser extent in the possibly absorbing contact structure, as a result of which the efficiency of the radiation-emitting semi-egg component is advantageously increased.

0064The insulation layer contains, for example, a silicon nitride, such as SiN, or other suitable materials.

0065Furthermore, a trench can be formed in the part of the semiconductor layer sequence arranged between the active zone and the first mirror, which preferably runs completely, in particular completely, around the contact structure projected into the plane of this part of the semiconductor layer sequence. This trench is preferably at least partially, particularly preferably completely, filled with the material of the insulation layer. A region of the part of the semiconductor layer sequence arranged between the first mirror and the active zone that is enclosed by the trench is accordingly electrically separated from the contact structure. This reduces radiation generation under the contact structure. The trench can extend in the vertical direction from the side of the semiconductor layer sequence adjoining the intermediate layer to the edge of the active zone or, if appropriate, to the active zone.

0066Further features, advantages and expediencies of the invention result from the descriptions of the following exemplary embodiments in conjunction with the following figures.

Show it

0067<dl id="dl0001"><dt>Figure 1a</dt><dd>2 shows a schematic sectional view of a first exemplary embodiment of a radiation-emitting semiconductor component according to the invention,</dd><dt>Figure 1b</dt><dd>a schematic sectional view of an embodiment for a semiconductor layer sequence in a radiation-emitting semiconductor component according to the invention and</dd><dt>Figure 2</dt><dd>is a schematic sectional view of a second embodiment of a radiation-emitting semiconductor device according to the invention.</dd></dl>

0068Identical, identical and identically acting elements are provided with the same reference symbols in the figures.

0069FIG. 1a shows a schematic sectional view of a first exemplary embodiment of a radiation-emitting semiconductor component according to the invention.

0070A semiconductor layer sequence 1 with a radiation-generating active zone 2 is followed by an electrically conductive and radiation-permeable intermediate layer 3 and this in turn is followed by a metal layer 4. The metal layer 4 is connected to a carrier 6 via a connecting layer 5.

0071The metal layer 4 and the intermediate layer 3 are part of a first mirror 7 of the radiation-emitting semiconductor component.

0072The electrical contacting of the component takes place in this exemplary embodiment via the electrodes 8 and 9. Since the electrode 8 is arranged on the side of the carrier 6 facing away from the first mirror 7, the latter is preferably doped to increase its conductivity or has a correspondingly high level Conductivity on. The semiconductor layer sequence 1 is electrically conductively connected to the electrode 8 via the metal layer 4, the electrically conductive and radiation-permeable intermediate layer 3, the carrier 6 and the connecting layer 5.

0073Radiation 200 generated in the operation of the component in the active zone 2 leaves the active zone in the direction of the first mirror 7. A first radiation component 201 is reflected at the interface of the intermediate layer 3 with the semiconductor layer sequence 1 and a further radiation component 202 is reflected at the metal layer 4. The intermediate layer is preferably designed in such a way that the radiation components 201 and 202 are structurally superimposed. The reflection on the first mirror can be used particularly efficiently.

0074A thickness D or D suitable for structural superimposition_re For this purpose, the intermediate layer can be determined in accordance with the stipulations given above and the intermediate layer can be dimensioned accordingly.

0075With a first mirror 7 of this type, reflectivities of over 90% can already be achieved, particularly in the visible spectral range.

0076If higher reflectivities of the first mirror are required, a Bragg mirror can be integrated in the semiconductor layer sequence 1 on the side of the intermediate layer 3 in order to increase the reflectivity of the first mirror 7. This is indicated in FIG. 1 a by extending the first mirror 7 into the semiconductor layer sequence. In such a first mirror, fewer pairs of semiconductor layers are necessary than in a first mirror of the same reflectivity, which is designed exclusively as a Bragg mirror. The heat dissipation from the component is improved by the smaller number of interfaces and the generally higher thermal conductivity of the metal layer compared to the semiconductor material of the Bragg mirror. The carrier 5 is preferably designed as a heat sink.

0077Depending on the design of the semiconductor layer sequence 1 and / or the resonator, such a component can be used as a coherent laser radiation-emitting component in the form of a VECSEL or as an incoherent radiation from spontaneous emission component in the form of an RCLED, for example with an internal resonator (not shown, see FIG. 1b) ), will be realized. Furthermore, the invention is also suitable for further semiconductor components, for example a laser, such as a VCSEL with an internal resonator, or an LED without a resonator.

0078An optical resonator of the component can be formed as an internal resonator, in particular for an RCLED, or as an external resonator, in particular for a VECSEL, with the first and a second mirror. For a laser component, in particular a VECSEL, the electrode 8, deviating from the illustration, is preferably designed as a ring electrode at the edge of the semiconductor layer sequence with a central region of the semiconductor layer sequence free of the electrode.

0079FIG. 1b shows a schematic sectional view of an exemplary embodiment of a semiconductor layer sequence 1 of a radiation-emitting semiconductor component according to the invention, as can be formed in FIG. 1a.

0080In this example, a semiconductor layer sequence 1 is shown for an RCLED.

0081The semiconductor layer sequence 1, the active zone 2 thereof, for example, on the III-V semiconductor material system In_x Ga Al_1-xy P, with 0≤x≤1, 0≤y≤1 and x + y≤1, is preferably grown epitaxially on a growth substrate 10, such as GaAs. An etch stop layer 11, preferably made of In, is on the growth substrate 10_0,5Al_0,25Ga_0,25P, arranged, which prevents the adverse effects of the action of an etchant on the subsequent layers. Typically 1-10 grown on this layer<i>µ</i>m thick current spreading layer 12, for example made of n-conducting Al_0,8Ga_0,2As, there follows a Bragg mirror 13 with, for example, 4 to 10 pairs of semiconductor layers, each having a layer 14 with a low refractive index, preferably made of n-conducting Al_0,95Ga_0,05As and a layer 15 with a higher refractive index, for example made of n-conducting Al_0,5Ga_0,5As, comprise, the high-index layer 14 of the respective pair is preferably arranged on the part of the active zone 2. The layer thickness of the respective layers of the Bragg mirror 13 is given by approximately a quarter of the wavelength of the radiation generated in this layer.

0082Around the active zone 2, which has a layer sequence 2a, 2b, 2c, for example in the order In_0,6Ga_0,4Pin code_0,5Ga_0,25Al_0,25P and again In_0,6Ga_0,4P, each with a thickness of approximately 5 nm, and embodied, for example, as a double heterostructure or quantum film package, are an n-type waveguide layer 16a and a p-type waveguide layer 16b, preferably each made of In_0,5Ga_0,25Al_0,25P, arranged, of which the layer 16a via an n-conductive barrier layer 17, for example made of n-In_0,5Al_0,5P, is connected to the Bragg mirror 13. The waveguide layer 16b is with the p-conducting side of the semiconductor layer sequence 1 via a p-conducting barrier layer 18, for example made of p-In_0,5Al_0,5P, connected. This is followed by a p-type Bragg mirror 19 which is designed in accordance with the Bragg mirror 13 and which, for example, has 4 or fewer pairs of semiconductor layers, in particular one pair to 4 pairs, with a low-index layer 20, for example made of p-type Al_0,95Ga_0,05As, and a layer 21 with a higher refractive index, such as p-type Al_0,5Ga_0,5As, includes.

0083The barrier layers 17 and 18 serve to enclose charge carriers in the active zone, which results in an increased charge carrier recombination in the active zone and thus an increased efficiency of the component.

0084After the epitaxial growth of the semiconductor layer sequence shown in FIG. 1b on the growth substrate 10, a radiation-permeable and electrically conductive intermediate layer 3, as shown in FIG. 1a, can be applied on the p-side, for example made of ZnO, preferably doped with Al. This can be done just like the subsequent application of the metal layer 4, for example an Au layer, for example by sputtering or vapor deposition.

0085Such an intermediate layer 3 advantageously improves the adhesion of the Au layer to the semiconductor layer sequence by virtue of an increased adhesion compared to Au on the adjacent III-V semiconductor material. Furthermore, the intermediate layer advantageously improves the electrical contact of the Au layer with the semiconductor layer sequence, preferably by diffusion of Zn atoms, which can act as acceptors, into the adjacent III-V semiconductors. This ensures homogeneous, low-loss energization of the active zone 2 from the p-side, since both the metal layer 4 and the intermediate layer 3 have a high conductivity, in particular in the lateral direction. A p-conducting AlGaAs-containing semiconductor layer is particularly suitable for forming an ohmic contact to the semiconductor layer sequence by means of an intermediate layer containing ZnO adjacent to the semiconductor layer.

0086A homogeneous current distribution through the current spreading layer 12 in the semiconductor layer sequence 1 is achieved on the n side of the semiconductor layer sequence. Compared to a component with two current spreading layers, one on the n side and one on the p side, formed in the semiconductor layer sequence 1, the epitaxial time can be shortened.

0087The metal layer can subsequently be connected to the carrier 6, which preferably contains GaAs and / or is designed as a heat sink, via a connecting layer 5, for example a solder or bond layer. If the semiconductor layer sequence is attached to the carrier by means of eutectic bonding with suitable metal layers, the connection layer can optionally comprise a multilayer system. The growth substrate 10 is then detached, for example by etching, mechanical loading or a laser detachment process, and the electrodes 8, 9, for example in the form of contact metallizations, are arranged on the semiconductor layer sequence and on the side of the carrier facing away from it.

0088The metal layer 4, the intermediate layer 3 and the p-side Bragg mirror 19 form the first mirror 7 of the RCLED, which together with the n-side Bragg mirror 13 represents the internal optical resonator of the component.

0089Because of the highly absorbent structure with the metal layer 4 and the GaAs carrier 6, the second mirror 13 arranged on the side of the active zone facing away from the carrier is expediently designed as a coupling-out mirror.

0090The emission wavelength λ of such an RCLED is in the visible, for example in the red, spectral range, at approximately 650 nm.

0091The thickness of the intermediate layer is approximately 70 nm for this wavelength. The thickness of the intermediate layer is thus about the penetration depth d_M≈30nm compared to the thickness D_id= λ / (4n_e.g.) ≈ 100nm of the intermediate layer for an ideal metal layer, the refractive index n_e.g. the intermediate layer at the above wavelength for ZnO is approximately 1.6. The depth of penetration d_M results from the equation (5) with the phase Φ_re≈2.2 by the reflection at the Au layer, which is calculated from the Fresnel formulas with the complex refractive index of Au, which has a high imaginary part.

0092This advantageously has the effect that the highest possible proportion of the radiation on the side of the intermediate layer 3 facing the active zone 2 and the radiation components reflected on the metal layer 4 interfere constructively and the reflectivity of the first mirror 7 is not reduced by destructive interference.

0093The Bragg mirror 13 advantageously has a reflectivity of 90% or less, in order in particular not to reduce the coupling-out efficiency of the spontaneously emitted radiation, which in RCLEDs is also influenced, inter alia, by the reflectivity of the coupling-out mirror.

0094In contrast, with such a configuration of the semiconductor layer sequence 1, the first mirror 7 has a higher reflectivity of approximately 98% and an advantageously low penetration depth, so that the thickness compared to a pure Bragg mirror of the same reflectivity, which for λ≈650nm comprises approximately 23 of the above-mentioned semiconductor layer pairs should be reduced. The active zone 2 can thus be arranged close to the virtual first mirror, which advantageously increases the efficiency of the RCLED.

0095Furthermore, the active zone 2 is preferably arranged in the resonator in such a way that, when the component is in operation, it is located in a wave antinode of a standing wave formed in the resonator. The efficiency of the radiation-emitting component can thus be further increased by coupling to the maximum electrical field strength of the standing wave. In particular, when positioning the active zone 2, the heat generated during operation of the component and the resulting expansion of the individual components of the component, in particular in the semiconductor layer sequence, must be taken into account, so that the active zone is arranged in a wave antinode during operation of the component.

0096Another advantage of such a first mirror 7 lies in the low directional dependence of the reflectivity on the metal layer 4, which is almost independent of the angle of incidence of the radiation relative to the surface normal of the mirror. Radiation leaving the active zone at a large angle to the surface normal, on the other hand, cannot be reflected or can only be reflected poorly by a pure Bragg mirror and can therefore only be coupled out of the component to a small extent.

0097However, radiation incident at a large angle is also highly reflected on the metal layer 4. This can subsequently be absorbed by the active zone 2 and possibly re-emitted so that it is coupled out of the component (so-called photon recycling). In this way, in particular in the case of an active zone 2 with high quantum efficiency, such as can be implemented in InGalP-based components, the probability is increased that a photon once generated is coupled out. In particular, this also applies to photons, which would otherwise be subject to a continued total reflection in the resonator, which occurs even at comparatively large angles - larger than the critical angle of the total reflection. This further improves the efficiency of the RCLED.

0098It should be noted that the semiconductor layer sequence can also be formed for a VECSEL, a VCSEL or an LED with a first mirror without a resonator, with minor structural changes.

0099FIG. 2 shows a schematic sectional view of a second exemplary embodiment of a radiation-emitting semiconductor component according to the invention.

0100This differs from the exemplary embodiment shown in FIG. 1 a essentially by an insulation layer 22, which is arranged in a recess in the intermediate layer 3 and the metal layer 4. The semiconductor layer sequence 1 can also be designed as in FIG. 1b.

0101This electrical insulation layer 22, for example made of SiN, is arranged under the region of the active zone 2, which is covered or shaded by the electrode 9, which contains, for example, an absorbent metal, and advantageously reduces the proportion of current that is generated by the electrode 8 flows into this area of ​​active zone 2. The area of ​​the semiconductor layer sequence covered by the electrode 9 is shown in dashed lines in FIG. The insulation layer can be applied by means of sputtering or vapor deposition.

0102Due to the insulation layer, only a low radiation power is generated in this area compared to the rest of the active zone 2. The proportion of radiation that can be absorbed by the electrode 9 is thus advantageously reduced and the overall efficiency of the component is further increased compared to that shown in FIG. 1a.

0103The cutout need not necessarily extend through the metal layer 4 and the intermediate layer 3 to the carrier 6. It is only essential that the lowest possible current reaches the area of ​​the active zone 2 covered by the electrode 9. A cutout in the intermediate layer or the metal layer alone can be sufficient for this.

0104Preferably, at least one trench 23, preferably encircling the electrode, is formed in the semiconductor layer sequence, which further reduces radiation generation under the electrode 8 in the active zone 2, which can be caused by a current flow around the insulation layer 22. The trench 23 is expediently filled with the material of the insulation layer. Such a trench can be structured from the semiconductor layer sequence, for example before the application of the intermediate layer, by means of an etching process. In FIG. 2, the trench extends in the vertical direction between the active zone and the side of the semiconductor layer sequence facing the intermediate layer, preferably from the intermediate layer to the edge of the active zone, in order to reduce the risk of damage to the active zone due to the structuring of the trench. The region of the semiconductor layer sequence enclosed by the trench is particularly preferably electrically separated from the remaining region via the insulation material.

0105Overall, an RCLED can be realized by means of the first mirror, which has an external efficiency of 30% or more, preferably up to 40%.

0106It should be noted that the invention is also suitable for an efficient VCSEL with an internal resonator or an efficient LED without a resonator with a first mirror. A particularly high increase in efficiency can be achieved with an RCLED or a VECSEL.

0107This patent application claims the priority of German patent application DE 102004057802.8 dated November 30, 2004, the entire disclosure content of which is hereby explicitly incorporated into the present patent application by reference.

0108The description of the invention with reference to the exemplary embodiments is not to be regarded as a limitation of the invention to these. Rather, the invention encompasses all combinations of features that are mentioned in the exemplary embodiments, the other description or the patent claims, even if these combinations are not the subject of a patent claim.