Light emitting diodes with graded composition active regions

Light-emitting diode with gradual component active area

Figure 1 shows the previous skills In _x Al _y Ga _lxy A schematic diagram of the energy band structure of a part of the N light-emitting device.

Fig. 2 shows In according to a specific embodiment of the present invention _x Al _y Ga _lxy Schematic diagram of N LED.

Fig. 3 shows the In Fig. 2 according to a specific embodiment of the present invention _x Al _y Ga _lxy Schematic diagram of the active area of NLED.

FIG. 4 is a schematic diagram of the energy band structure of a part of a specific embodiment of the active region in FIG. 3.

Figure 5A shows the previous technique In _x Al _y Ga _lxy Part of the simulated energy band structure of the N light-emitting device.

FIG. 5B shows a simulated energy band structure of a part of a specific embodiment of the active region in FIG. 3.

FIG. 6 is a schematic diagram of the energy band structure of a part of another embodiment of the active region in FIG. 3.

Figure 7 shows the previous skills In _x Al _y Ga _lxy The simulated energy band structure of the other part of the N light-emitting device.

As shown in Figure 8. According to another embodiment of the present invention, the In _x Al _y Ga _lxy Schematic diagram of the active area of the N LED.

The system shown in Fig. 9 contains the active area of Fig. 8 in Fig. 2In _x Al _y Ga _lxy An analog energy band structure of a specific embodiment of the NLED.

The present invention relates to general semiconductor light-emitting devices, and more specifically, it relates to improving the light output of the active region in the light-emitting device.

III-Nitride light-emitting devices are based on semiconductor alloys composed of nitrogen and group III elements in the periodic table. Such III-nitride components include In _x Al _y Ga _lxy N light-emitting diodes (LED) and laser diodes (LD).

In _x Al _y Ga _lxy The active area of N LED and LD usually includes one or more In _x Al _y Ga _lxy N quantum well and barrier layer. The layers usually include alloy compositions that are different from each other and different from the surrounding layers of the element. Due to the differences in these ingredients, in In _x Al _y Ga _lxy The layers in the active area of the N light-emitting device are usually subjected to biaxial tension. Departments that should be paid attention to, in In _x Al _y Ga _lxy N represents the formula, 0x1,0y1, and x+y1.

In _x Al _y Ga _l - _x - _y N crystal, such as In _x Al _y Ga _lxy The crystals in N light-emitting devices usually adopt wurtzite or zinc sulfide crystal structure. Both of the two crystal structures are piezoelectric structures. That is, when under pressure, both structures will generate an internal electric field. In addition, the low symmetry of the wurtzite crystal structure will produce spontaneous polarity. As In _x Al _y Ga _l - _x - _y The relationship between the biaxial tension and piezoelectric properties of N and the spontaneous polarity (if any), even if In _x Al _y Ga _lxy The N light-emitting device is not biased, and the quantum well layer and barrier layer in the device usually have a strong internal electric field.

For example, the prior art shown in Figure 1 is not biased. _x Al _y Ga _lxy The energy band structure diagram of a part of the active region of the N LED, which includes the GaN barrier layer 2, In _x Ga _lx N quantum well layer 4, and GaN barrier layer 6. The two horizontal axes in FIG. 1 represent the position of the active area in the direction perpendicular to the layers. The interfaces of these layers are represented by dashed lines. The lower vertical axis represents the energy at the edge 8 of the conduction energy band and the edge 10 of the valence energy band in the various layers. The upper vertical axis represents the concentration of indium in the alloy used to form the various layers. Layers 2, 4, and 6 are all wurtzite crystal structures. The c-axis of the crystal is substantially perpendicular to the layer and extends from layer 2 to layer 6. In the active region of the prior art, the molar ratio of indium in the entire width of the quantum well layer 4 is constant.

If there is no spontaneous polarity, piezoelectric electric field, and external bias voltage, the conduction energy band edge 8 and the atomic valence energy band edge 10 in each layer may be very flat. However, in the energy band structure shown in FIG. 1, the piezoelectric electric field has already caused the edge of the energy band to tilt. Such a tilt phenomenon will negatively affect the performance of the light-emitting device having the active area as shown in the figure. For example, due to the tilt relationship, the electron wave function 12 and the hole wave function 14 will be concentrated in In _x Ga _lx Both sides of the N quantum well layer 4. Because of the influence of the piezoelectric electric field, the spatial overlap of these wave functions is reduced, thereby reducing the probability of spontaneous and excitable luminescence in the active region, and increasing the non-radiative release or leakage of electrons and holes after they are injected into the active region. The probability of going outside the active area. Therefore, the piezoelectric electric field will reduce the In _x Al _y Ga _lxy NLED operating efficiency and In _x Al _y Ga _lxy Optical gain of N LD. Therefore, the piezoelectric electric field will make it difficult to achieve high-brightness In _x Al _y Ga _lxy N LED and low critical value In _x Al _y Ga _lxy N LD.

In _x Al _y Ga _lxy Another result of the piezoelectric field in the N light-emitting device is to reduce the light-emitting energy. However, part of the charge emitted during the operation of the device will sweep the piezoelectric electric field, and the emission energy will increase due to the increase of the carrier density in the quantum well layer. In a quantum well layer with a high indium content, this kind of transfer will cause a drastic change in color due to the change of the emitted current.

Therefore, what is needed is an In _x Al _y Ga _lxy N light-emitting devices in which the problems related to the piezoelectric electric field have been improved.

The light emitting device according to the embodiment of the present invention includes a first semiconductor layer with a first surface composed of a first conductivity type, and an active region covering the first semiconductor layer. The active region includes a second semiconductor layer, which may be a quantum well layer or a barrier layer. The second semiconductor layer is composed of a III-nitride semiconductor alloy having a graded composition in a direction substantially perpendicular to the first surface of the first semiconductor layer. The light emitting device also includes a third semiconductor layer composed of the second conductivity type covering the active area.

The second semiconductor layer may be piezoelectric and, for example, composed of wurtzite crystal structure. In one of the implementation manners, the molar ratio of the III-nitride semiconductor alloy may gradually change in an asymmetric manner, for example, linearly. The composition of the III-nitride semiconductor alloy may be graded in order to reduce the effect of the piezoelectric electric field in the active region. In one of the implementations, the III-nitride semiconductor alloy is In _x Al _y Ga _lxy N, and the molar ratio of indium is gradual. In another implementation mode, the III-nitride semiconductor alloy is In _x Al _y Ga _lxy N, and the molar ratio of aluminum is gradual.

In one of the specific embodiments, the active region includes a plurality of quantum well layers and at least one barrier layer. The barrier layer is composed of a III-nitride semiconductor alloy, and the molar ratio of indium is gradually gradual in a direction substantially perpendicular to the first surface of the first semiconductor layer. In one of the implementation modes, the III-nitride semiconductor alloy is In _x Al _y Ga _lxy N. The molar ratio of indium in the barrier layer is gradually changed in an asymmetric manner, for example, linearly, and may be gradually changed in order to reduce the effect of the piezoelectric electric field in the active region. The barrier layer may be one of a plurality of barrier layers included in the active region, and each system is composed of a III-nitride semiconductor alloy, and the molar ratio of indium is substantially perpendicular to that of the first semiconductor layer. The direction of the first surface is gradual.

The advantage is that in the light-emitting devices according to several specific embodiments of the present invention, the phenomenon of separation of electrons and holes caused by the piezoelectric field in the active region of the light-emitting device of the prior art has been substantially reduced. At the same time, in some embodiments, the voltage required to drive the light-emitting device is relatively low. Therefore, the efficiency of the light-emitting device according to some embodiments of the present invention is higher than that of the pre-fiber technology element. In addition, in some specific embodiments, when the carrier density in the active region increases, the emission wavelength of the light-emitting device does not substantially undergo blue shift.

Schematic description

Figure 1 shows the previous skills In _x Al _y Ga _lxy A schematic diagram of the energy band structure of a part of the N light-emitting device.

Fig. 2 shows In according to a specific embodiment of the present invention _x Al _y Ga _lxy Schematic diagram of N LED.

Fig. 3 shows the In Fig. 2 according to a specific embodiment of the present invention _x Al _y Ga _lxy Schematic diagram of the active area of NLED.

FIG. 4 is a schematic diagram of the energy band structure of a part of a specific embodiment of the active region in FIG. 3.

Figure 5A shows the previous technique In _x Al _y Ga _lxy Part of the simulated energy band structure of the N light-emitting device.

FIG. 5B shows a simulated energy band structure of a part of a specific embodiment of the active region in FIG. 3.

FIG. 6 is a schematic diagram of the energy band structure of a part of another embodiment of the active region in FIG. 3.

Figure 7 shows the previous skills In _x Al _y Ga _lxy The simulated energy band structure of the other part of the N light-emitting device.

As shown in Figure 8. According to another embodiment of the present invention, the In _x Al _y Ga _lxy Schematic diagram of the active area of the N LED.

The system shown in Fig. 9 contains the active area of Fig. 8 in Fig. 2In _x Al _y Ga _lxy An analog energy band structure of a specific embodiment of the NLED.

It should be noted that the sizes in the various drawings do not necessarily have to be scaled. However, the same reference symbols in the various drawings will represent the same components in various specific embodiments.

According to a specific embodiment of the present invention, the active area of a semiconductor light emitting device includes a semiconductor alloy with a graded composition. This article will describe several specific embodiments, in which the active region includes one or more gradient component quantum well layers and/or one or more gradient component barrier layers.

Referring to Figure 2, in one of the specific embodiments, In _x Al _y Ga _lxy The N-based LED 16 includes a multilayer epitaxial structure 18 placed on the buffer layer 20, and then placed on the blue solid stone substrate 22. The epitaxial structure 18 includes an In _x Al _y Ga _lxy N area 26 and below In _x Al _y Ga _lxy Active area 24 between N areas 28. In _x Al _y Ga _lxy N region 28 includes n-type and/or undoped In _x Al _y Ga _lxy N layer. Active area 24 includes In _x Al _y Ga _lxy One or more quantum well layers and one or more barrier layers composed of N. The ohmic p-contact 30 and the metal layer 32 will be electrically coupled to each other and will be coupled to the upper In _x Al _y Ga _lxy N area 26. Ohm n-contact 34 will be electrically coupled to the lower In _X Al _y Ga _lxy N area 28. Applying an appropriate forward-biased electric field between the contacts 30 and 34 can emit light from the active area 24.

3, in one of the specific embodiments, the active region 24 includes In _x Ga _lx The N quantum well layers 36, 40 and 44, and the GaN barrier layers 38, 42 and 46, wherein the quantum well layer 36 is located closest to the sapphire substrate layer 22 (FIG. 2). The thickness of the quantum well layers 36, 40, and 44 ranges from about 10 angstroms () to about 100 (usually about 30 ). The thickness of the barrier layers 38, 42 and 44 ranges from about 25 angstroms () to about 500 (usually about 100 ). Although FIG. 3 shows three quantum well layers and three barrier layers, in other specific embodiments, more or fewer such quantum wells and barrier layers may be included.

In one of the specific embodiments, the molar ratio of indium in one or more quantum well layers 36, 40 and 44 (In _x Ga _lx The subscript X in N) will become smaller and smaller with the distance from the substrate. For example, the molar ratio of indium in the quantum well layer 40 may decrease from a first value near the interface between the quantum well layer 40 and the barrier layer 38 to a value near the interface between the quantum well layer 40 and the barrier layer 42. The second value. Generally, the composition of each of the quantum well layers 36, 40, and 44 will show a gradual state in the same way.

When the molar ratio of indium increases, In _x Ga _lx The energy band gap of N will decrease. For example, if there is no electric field, such as a piezoelectric electric field, the gradual indium concentration that gradually decreases with the distance from the substrate in the entire quantum well will cause the gradual energy band in the quantum well to increase with the substrate. The distance gradually increases. In this case, the edge energy of the conduction energy band in the quantum well may increase with the distance from the substrate, but the edge energy of the atomic valence energy band in the quantum well may decrease with the distance from the substrate . However, generally speaking, the epitaxial structure 18 will have a (piezoelectric) wurtzite crystal structure, and its c-axis direction will be substantially perpendicular to the sapphire substrate 22 and away from the substrate. Therefore, piezoelectric electric fields usually exist in the quantum well layers 36, 40, and 44.

Advantages, in the whole In _x Ga _lx The gradual indium concentration in the N quantum well that gradually decreases with the distance from the substrate (that is, gradually decreases in a direction substantially parallel to the c-axis of the wurtzite crystal) can at least partially eliminate the piezoelectric electric field's effect on the quantum well. The effect of turning on the edge of the energy band. The result of this elimination can be regarded as the tilt of the edge of the conduction energy band caused by the indium concentration gradient at least partially compensates the tilt of the edge of the conduction energy band caused by the piezoelectric field. Of course, we can also regard the effect of the indium concentration gradient on the inclination of the edge of the conduction energy band as the effective electric field experienced by the electrons in the conduction energy band, which partially eliminates the piezoelectric electric field, and the effective electric field is related to the The composition gradient is correlated and opposite to the piezoelectric electric field.

If the quantum well is very thin, then the piezoelectric electric field for the In _x Ga _lx The edge effect of the conduction energy band in the N quantum well may be almost eliminated by the indium concentration gradient. In grown on the GaN layer _x Ga _lx The intensity of the piezoelectric electric field in the N quantum well (the molar ratio of indium is x) is approximately: E _Pz = (7 million volts per centimeter). x (this estimated value is equivalent to a piezoelectric field of 7 million volts per centimeter of the InN layer grown on the GaN layer). If the indium concentration in the direction of the wurtzite c-axis changes from the molar ratio x to the molar ratio x=0, then the thickness L is in centimeters _x Ga _lx The effective electric field suffered by electrons in the conduction energy band of the N quantum well is: E _eff = (1.05 Volts/L). x predicted value of the latter hypothesis In _x Ga _lx The linear energy band gap of N is related to the composition, and about 70% of the 1.5 electron volt (eV) energy band gap difference between InN and GaN occurs in this conduction energy band. After combining these electric field equations, it can be roughly predicted that the effect of the piezoelectric electric field on the edge of the conduction energy band will be approximately neutralized to: when L~15, the linear gradual component In _x Ga _lx What is the width of the N quantum well layer?

4 is a schematic diagram of the energy band structure of a part of the active region 24, which includes GaN barrier layers 38 and 42 and a thin In _x Ga _lx N quantum well layer 40, in one of the specific embodiments, the In _x Ga _lx The molar ratio of indium in the N quantum well layer 40 will gradually linearly decrease from its maximum value near the interface with the barrier layer 38 to a value near the interface with the barrier layer 42 about zero. The inclination of the conduction energy band edge 48 in the quantum well layer 42 has been substantially reduced to be equivalent to the inclination of the conduction energy band edge 8 in the prior art quantum well layer 4 in FIG. 1.

However, the inclination of the valence energy band edge 50 in the thin quantum well layer 42 is equivalent to or slightly higher than that in the prior art quantum well layer 4. The tilt of the valence energy band edge 50 can be regarded as the tilt of the valence energy band edge 50 caused by the indium concentration gradient plus the tilt of the valence energy band edge 50 caused by the piezoelectric field. We can also regard the effect of the indium concentration gradient on the edge 50 of the valence energy band as the effective electric field experienced by the electrons in the valence energy band strengthens the piezoelectric electric field, and the effective electric field is related to the composition gradient. .

The advantage is that in the gradual In _x Ga _lx In the N quantum well, the In of the previous technique has almost been reduced _x Ga _lx The phenomenon of separation of electrons and holes that occurs in the N quantum well. Especially in the specific embodiment shown in FIG. 4, the electrons and holes in the quantum well layer 40 are concentrated near the interface between the quantum well layer 40 and the barrier layer 38. Therefore, the efficiency of the light-emitting device according to the present invention is higher than that of the prior art element. In addition, when the carrier density in the quantum well layer increases, the emission wavelength of the light-emitting device according to the present invention does not substantially undergo blue shift.

Even if the thickness of the quantum well layer exceeds 15, because the entire In _x Ga _lx The gradual indium concentration in the N quantum well that gradually decreases with the distance from the substrate may still shorten In _x Ga _lx The distance between electrons and holes in N. For example, the conventional analog energy band structure of the active region of the prior art shown in FIG. 5 includes GaN barrier layers 2 and 6 and In _0.4 Ga _0.6 The N quantum well layer 4 has a forward bias of about 2.5 volts. The thickness of the barrier layers 2 and 6 is about 100. The quantum well layer 4 has a thickness of about 40° and a spatially uniformly distributed indium concentration. The conduction energy band edge 8 and the atomic valence energy band edge 10 in the quantum well layer 4 are inclined in the same manner as in FIG. 1. In contrast, the simulated energy band structure of the active region 24 shown in FIG. 5B (forward bias is about 2.5 volts), in which the thickness of the GaN barrier layers 38 and 42 is about 100, and the thickness of the quantum well layer 40 is about 40, And In _x Ga _lx The molar ratio of indium in the N quantum well layer 40 will gradually linearly decrease from approximately x=0.4 near the interface between it and the barrier layer 38 to approximately X=0 near the interface between it and the barrier layer 42. Compared with the on-energy band edge 8 in FIG. 5A, the on-energy band edge 48 becomes relatively flat. As shown in the specific embodiment shown in FIG. 4, the electrons and holes in the quantum well layer 40 are concentrated near the interface between the quantum well layer 40 and the barrier layer 38. Therefore, this specific embodiment also has the advantages of the specific embodiment shown in FIG. 4.

In another specific embodiment, the molar ratio of indium in one or more of the quantum well layers 36, 40, and 44 gradually increases with the distance from the substrate. For example, the molar ratio of indium in the quantum well layer 40 may decrease from a first value near the interface between the quantum well layer 40 and the barrier layer 38 to a value near the interface between the quantum well layer 40 and the barrier layer 42. The second value. Advantages, in the whole In _x Ga _lx The gradually increasing gradual indium concentration in the direction of the N quantum well substantially parallel to the c-axis of the wurtzite crystal can at least partially eliminate the effect of the piezoelectric electric field on the edge of the atomic valence energy band in the quantum well. The result of this elimination can be regarded as the same as the above-mentioned effect of eliminating the piezoelectric electric field on the edge of the conduction energy band.

6 is a schematic diagram of the energy band structure of a part of the active region 24, which includes GaN barrier layers 38 and 42 and a thin In _x Ga _lx N quantum well layer 40, in one of the specific embodiments, the In _x Ga _lx The molar ratio of indium in the N quantum well layer 40 will gradually linearly increase from about zero near the interface with the barrier layer 38 to about the maximum value near the interface with the barrier layer 42. The inclination of the valence energy band edge 50 in the quantum well layer 42 has been substantially reduced to be equivalent to the inclination of the valence energy band edge 10 in the prior art quantum well layer 4 in FIG. 1. The inclination of the edge of the conduction energy band in this specific embodiment can be regarded as the same as the inclination of the edge of the atomic valence energy band in the specific embodiment shown in FIG. 4.

In this specific embodiment, the In _x Ga _lx The phenomenon of separation of electrons and holes that occurs in the N quantum well. Especially in this embodiment, the electrons and holes in the quantum well layer 40 tend to be concentrated near the interface between the quantum well layer 40 and the barrier layer 42. Therefore, this embodiment also has the advantages of the embodiment shown in FIGS. 4 and 5B.

It is shown from the above specific examples that no matter in In _x Ga _lx In the direction of the N quantum well substantially parallel to the c-axis of the wurtzite crystal, gradual increase or decrease of the indium concentration can obtain benefits. In the active region where the edge shift of the conduction energy band between the quantum well and the barrier layer is larger than the edge shift of the atomic valence energy band, it is generally advantageous that the indium concentration can gradually decrease in the direction of the c-axis. In the active region where the edge deviation of the conduction energy band between the quantum well and the barrier layer is smaller than the edge deviation of the atomic valence energy band, it is generally advantageous that the indium concentration can be gradually increased in the direction of the c-axis.

Although in the specific embodiments shown in FIGS. 4, 5B and 6, the molar ratio of indium in the quantum well layer 40 is linearly gradual, the molar ratio of indium in one or more quantum well layers in the active region 24 is Other functional relationships can also be present between the positions. For example, the molar ratio of indium may change in an exponential, parabolic, or step-wise manner. Similarly, although in the specific embodiments shown in FIGS. 4, 5B, and 6, the molar ratio of indium in the quantum well layer 40 is monotonically decreasing or increasing, the molar ratio of indium may also be in the quantum well. A maximum value and/or one or more local maximum values at one or more intermediate positions. Generally speaking, in accordance with specific embodiments of the present invention, In _x Ga _lx In the N quantum well, the relationship between the molar ratio of indium and the position is asymmetric with respect to a plane parallel to the barrier layer and approximately in the center of the quantum well.

In the gradual In _x Ga _lx In the N quantum well, for example, the molar ratio of indium may change from approximately x=0.5 to approximately x=0. The molar ratio of indium in the graded quantum well may be greater than zero at the interface between the quantum well and the barrier layer. That is, the molar ratio of indium does not necessarily have to be gradually changed to x=0.

In In _x Al _y Ga _lxy The slope of the edge of the conduction energy band in the active area barrier layer of the N light-emitting device will also have a negative impact on the performance of the device. Figure 7 shows the previous skills In _x Al _y Ga _lxy A part of the conventional analog conduction energy band edge 52 of the N light-emitting device, which includes the GaN layer 54, the GaN barrier layers 58, 62 and 66, and In _0.4 Ga _0.6 The N quantum well layers 56, 60 and 64 have a forward bias of about 2.5 volts. The inclination of the edge 52 of the conduction energy band in the GaN layers 54, 58, 62, and 66 creates triangular potential barriers 68, 70, and 72. Electrons must be ejected between these potential barriers, which will lead to an unfavorable increase in the voltage of the diode transistor.

By gradually changing the composition of one or more layers of the barrier layer, it is possible to reduce the inclination of the edge of the conduction energy band in the barrier layer. Referring to FIG. 8, for example, in one of the specific embodiments, the active area 24 (FIG. 2) of the LED 16 includes In _X2 Ga _l-x2 Quantum well layers 74, 78 and 82 of N, and In _xl Ga _l - _xl N barrier layers 76, 80 and 84, of which the quantum well layer 74 is located closest to the sapphire substrate layer 22 (Figure 2). The molar ratio x2 of indium in the quantum well layers 74, 78 and 82 is uniformly distributed in space. However, the molar ratio x1 of indium in one or more of the barrier layers 76, 80, and 84 will gradually change with the distance from the substrate 22. For example, the molar ratio of indium in the barrier layer may gradually increase or decrease with the distance from the substrate 22. The relationship between the molar ratio of indium and the position in the barrier layer may be, for example, linear, exponential, parabolic, or stepwise. The molar ratio of indium in the barrier layer may have a maximum value and/or one or more local maximum values at one or more intermediate positions. Generally speaking, in the barrier layer, the relationship between the molar ratio of indium and the position is asymmetric.

Those familiar with the art may expect that the introduction of indium into the III-nitride barrier layer may negatively affect the performance of the device due to lowering the boundary between carriers. However, the inventor of this case discovered that in In _x Ga _lx It is advantageous to gradually change the molar ratio of indium in the N barrier layer. For example, the conventional analog conduction energy band edge 48 of a part of the LED 16 including the active area 24 shown in FIG. 9 according to a specific embodiment of the present invention has a forward bias of about 2.5 volts. In the implementation shown in Figure 9, the components in the quantum well layers 74, 78 and 82 are In _0.4 Ga _0.6 N, and the molar ratio of indium in each of the barrier layers 76, 80, and 84 will be from about x=0 near one side of each barrier layer along the direction of the wurtzite c axis (ie in Figure 8 The direction from bottom to top) gradually changes to about x=0.16 near the other side of each barrier layer. The advantage is that the height of the triangular potential barriers where electrons are emitted into the quantum well layers 74, 78, and 82 can be substantially reduced to be equivalent to the barriers 68, 70, and 72 in FIG. 7. In other implementations, the molar ratio of indium in the quantum well layer may be greater than or less than x2=0.4, and the molar ratio of indium in the barrier layer may be greater than 0.16.

In other specific embodiments, the active region 24 includes one or more graded composition quantum well layers and one or more graded composition barrier layers. Similarly, in other specific embodiments, the In _x Al _y Ga _lxy The molar ratio of aluminum in the N quantum well layer or barrier layer will gradually change in a direction substantially perpendicular to the layers. In some embodiments, the molar ratio of aluminum and the molar ratio of indium will gradually change.

Various In in the light-emitting device according to the embodiment of the present invention _x Al _y Ga _lxy The N layer may be formed by, for example, metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). The quantum well layer and barrier layer of graded composition may be formed, for example, by changing the flow rate of various reagent gases during the deposition of each layer.

Although the present invention has been illustrated with specific specific embodiments, it is hoped that the present invention can cover all changes and amendments in the scope of the appended patent application. For example, referring to FIG. 2 again, the substrate 22 may be made of materials other than sapphire, such as SiC. The metal layer 32 may be semi-transparent to the light emitted by the active area 24. Alternatively, the metal layer 32 may be highly reflective to the light emitted by the active area 24, and the LED 16 may be mounted in the form of a flip chip, and the contacts 30 and 34 may face the sub-base.

According to the present invention, the gradual component active region may be formed in other In _x Al _y Ga _lxy In the N light-emitting device, the element described in US Patent No. 6,133,589, which is assigned to the inventor of the present invention, is incorporated herein by reference. In addition, in contrast to the LED16 of FIG. 2, the In _x Al _y Ga _lxy The structure of the N light-emitting device may be that the n-type region covers the p-type region, and then a substrate is covered. The light-emitting device may be a laser diode.

According to the present invention, the gradual component active area may also be composed of other material systems, such as III-V material system and II-VI material system. This gradual active area is particularly advantageous for piezoelectric material systems and material systems with spontaneous polarity.