EP1407496A1

EP1407496A1 - Gallium nitride-based led and a production method therefor

Info

Publication number: EP1407496A1
Application number: EP02754397A
Authority: EP
Inventors: Berthold Hahn; Andreas Hangleiter; Volker HÄRLE
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2001-07-19
Filing date: 2002-07-19
Publication date: 2004-04-14
Also published as: US7482181B2; CN1533612A; DE10135189A1; JP2004535687A; TW550838B; CN100380687C; WO2003009399A1; US20040152226A1

Abstract

The invention relates to a method for producing a light-emitting device based on a gallium nitride-based compound semiconductor, comprising a light-emitting layer (2), which is provided with a first and a second main surface and formed from a compound semiconductor based on gallium nitride. The inventive device also comprises a first covering layer (3), which is connected to the first main surface of the light-emitting layer (2) and formed from an n-type compound semiconductor based on gallium nitride, whose composition differs from that of the compound semiconductor of the light-emitting layer. Lastly, the inventive device comprises a second covering layer (4), which is connected to the second main surface of the light-emitting layer (2) and formed from a p-type compound semiconductor based on gallium nitride, whose composition also differs from that of the compound semiconductor of the light-emitting layer. In order to improve the luminescence yield of the device (1), the thickness of the light-emitting layer (2) in the proximity of offsets (10) is less than in the remaining area.

Description

GALLIUM NITRIDE-BASED LED AND THEIR PRODUCTION PROCESS

Method for producing a light-emitting device based on a gallium nitride-based compound semiconductor and light-emitting device based on a gallium nitride-based compound semiconductor

The present invention relates to a method for producing a light-emitting device based on a gallium nitride-based compound semiconductor according to the

The preamble of claim 1 and a light-emitting device based on a gallium nitride-based compound semiconductor according to the preamble of claim 18.

In the following context, light-emitting devices or layers also include devices or layers which only or, among other things, emit UV radiation or IR radiation.

Compound semiconductors based on gallium nitride - these are III-V compound semiconductors that contain Ga and N, among others, such as gallium nitride (GaN), gallium aluminum nitride (GaAlN), indium gallium nitride (InGaN) and indium aluminum gallium nitride (InAlGaN) - have a direct band gap in the area from 1.95 to 6 eV and are therefore well suited for light-emitting devices, such as light-emitting diodes or laser diodes.

According to the present invention, a light-emitting device based on a gallium nitride-based compound semiconductor is already present if a light-emitting structure of the device contains at least one layer made of a gallium nitride-based compound semiconductor.

It was found that, for example, an active, ie light-emitting layer in the form of one or more so-called quantum films can be produced from InGaN light-emitting diodes are in the green (500 nm), blue (450 nm) or violet spectral range (405 nm) in a relatively narrow wavelength range (ie a relatively small FWHM) with a very high luminescence yield. Such light-emitting diodes are produced, for example, by organometallic chemical deposition (MOCVD) of a GaN buffer layer, a GaN layer doped with silicon, an AlGaN layer doped with silicon, a first coating layer of InGaN doped with silicon, the active, for example undoped InGaN layer, a second coating layer composed of magnesium-doped AlGaN and a magnesium-doped GaN layer. For blue light-emitting diodes, for example, In ₀ , ₂ Ga ₀ , ₈ and for violet light-emitting diodes, for example, In _0, ₉ Ga ₀ , ₉ N is selected as the active layer. Such a light-emitting device is described, for example, in S. Nakamura et al. : "High-Power InGaN Single-Quantum-Well-Structure Blue and Violet Light-Emitting Diodes", Appl. Phys. Lett. 67 (1995), pages 1868-1870.

Furthermore, EP 0 599 224 B1 is a light-emitting one

Apparatus known on which the preamble of claim 1 is based. This light-emitting device based on a gallium nitride-based compound semiconductor has a double heterostructure, with - a light-emitting layer with a first and a second main surface, which is formed from an In _x Gaι- _x N compound semiconductor with 0 <x <1 is;

a first cladding layer bonded to the first major surface of the light-emitting layer and made of an n-type compound semiconductor based on gallium nitride, the composition of which differs from that of the compound semiconductor of the light-emitting layer; and

a second coating layer which is connected to the second main surface of the light-emitting layer and is formed from a p-type compound semiconductor based on gallium nitride, the composition of which differs from that differs gene of the compound semiconductor of the light emitting layer. In order to improve the luminance or the light emission output power, the light-emitting layer is doped with a p-type foreign substance and / or an n-type foreign substance.

Starting from this prior art, it is an object of the present invention to develop a light-emitting device based on a gallium nitride-based compound semiconductor which has a further improved luminescence yield.

These objects are achieved by a method with the features of claim 1 and by a light-emitting device with the features of claim 18. Advantageous refinements and developments of the invention are the subject of dependent claims 2-17 and 19-32.

The light emitting device based on a gallium nitride-based compound semiconductor according to the present

The invention includes a light emitting layer having a first and a second main surface, which is formed from a compound semiconductor based on gallium nitride; a first cladding layer bonded to the first major surface of the light-emitting layer and formed from an n-type gallium nitride compound semiconductor; and a second cladding layer bonded to the second major surface of the light emitting layer and made of a p-type gallium nitride based compound semiconductor, the composition of the compound semiconductor of the light emitting layer being different from that of the compound semiconductors of the first and second cladding layers. The light-emitting layer and the first and second coating layers are formed in succession, preferably by means of an MOCVD process, on a substrate. The light emitting device according to the present invention is characterized in that the thickness the light-emitting layer near dislocations is less than in the rest of the area.

In particular on foreign substrates such as sapphire or silicon carbide (SiC), the known compound semiconductors based on gallium nitride have a very high dislocation density.

By reducing the thickness of the light-emitting layer in the vicinity of dislocations, shielding energy barriers are built up during the dislocations, which prevent diffusion of charge carriers towards the dislocations and thus prevent possible non-radiative recombination of electron-hole pairs at these dislocations ( Passivation of transfers). Even if it is partly assumed that the existing dislocations in the case of gallium nitride-based compound semiconductors, unlike the gallium phosphide or gallium arsenide-based compound semiconductors, do not serve as non-radiative recombination centers and therefore the density of the dislocations does not have any significant effects on the light output light-emitting devices constructed in this way (SD Lester et al.: "High Dislocation Densities in High Efficiency GaN-Based Light-Emitting Diodes", Appl. Phys. Lett. 66 (1995), pages 1249-1251 and T. Mukai et al.: "InGaN-Based Blue Light-Emitting Diodes Grown on Epitaxially Laterally Overgrown GaN Substrates", Jpn. J. Appl. Phys., Vol. 37 (1998), pages

L839-L841), higher luminescence yields were found in the light-emitting devices according to the present invention than in comparable conventional light-emitting devices. It is therefore assumed that the formation of shielding energy barriers at dislocations has a favorable effect on the light yield, since the recombination of charge carriers to a greater extent in areas with smaller band gaps, i.e. take place in optically active areas.

Preferably, the thickness of the light emitting layer in the vicinity of dislocations is reduced to less than that Half the thickness of the light-emitting layer in the remaining area.

In a preferred embodiment of the invention, the light-emitting layer is formed from an In _x Al _y Gaι_ _x - _y N compound semiconductor with 0 <x <1, O ≤ y ≤ l and x + y <1. The invention can in particular also advantageously be used for In-free light-emitting devices, ie for x = 0.

The light-emitting layer can be doped with a p-type foreign substance and / or an n-type foreign substance. The light-emitting layer is preferably an intrinsic quantum film of a quantum film structure, preferably an (preferably intrinsic) InGaN / GaN quantum film structure with at least one GaN quantum film.

The general concept of the invention, in order to build up an energy barrier in the vicinity of dislocations, to reduce the layer thickness in the vicinity of dislocations in order to increase the quantum yield, is particularly preferred for in-free radiation-emitting layers.

The invention is described below with reference to a preferred embodiment with reference to the accompanying drawings. In it show:

1 shows a schematic illustration of the basic structure of an exemplary embodiment of a light-emitting device according to the present invention; and

2 shows a schematic representation of an enlarged section of the light-emitting device from FIG. 1 with the associated energy profile of the band gap. The basic structure shown in FIG. 1 shows a light-emitting diode 1. However, the invention also extends to laser diodes as light-emitting devices.

The light-emitting diode 1 has a so-called double heterostructure 9, consisting of an active, ie light-emitting layer 2, a first n-type coating layer 3 and a p-type second coating layer 4. The light-emitting layer 2 is made of an In _x AlyGax _x .yN compound semiconductors with O ≤ x ≤ l, O ≤ y ≤ l and x + y ≤ 1 are formed and in particular also extend to In-free light-emitting diodes with an Al _y Gaι_ _y N compound semiconductor with 0 <y ≤ 1 (ie x = 0). The first coating layer 3 is formed from a Ga _u Alι_ _u N compound semiconductor with 0 <u 1 1 and the second coating layer 4 is formed from a Ga _v Alι_ _v N compound semiconductor with 0 <v <1. The composition of the compound semiconductor differs both in the first and in the second coating layer 3, 4 from that of the compound semiconductor in the light-emitting layer 2; the compositions of the compound semiconductors in the two coating layers 3 and 4 can be the same or different from one another.

The light emitting diode 1 emits ultraviolet light when x is close to 0, up to longer-wave red light when x is close to 1. In the range 0 <x <0.5, the light-emitting diode 1 emits blue to yellow light in the wavelength range from approximately 450 to 550 nm.

In addition to doping the first and the second coating layers 3 and 4 with n-type or p-type foreign substances, the light-emitting layer 2 with n-type foreign substances and / or p-type foreign substances can also be used to improve the luminescence yield of the light-emitting diode be endowed. For example, beryllium, magnesium, calcium, zinc, strontium and cadmium of the 2nd main group of the periodic table can be used as the p-type foreign substance, 2 zinc or in total for the light-emitting layer special magnesium is to be preferred. As an n-type foreign substance, for example silicon, germanium and tin of the IV. Main group of the periodic table or sulfur, selenium and tellurium of the VI. Main group of the periodic table can be used.

The first, n-type coating layer 3 has a layer thickness of approximately 0.05 to 10 μm and the second, p-type coating layer 4 has a layer thickness of approximately 0.05 μm to 1.5 μm. The layer thickness of the light-emitting layer 2 is preferably in the range from approximately 10 Å to 0.5 μm.

As shown in FIG. 1, the double heterostructure 9 is usually formed over a buffer layer 6 on a substrate 5. For example, sapphire, silicon carbide (SiC) or zinc oxide (ZnO) can be used as substrate 6. For the buffer layer 6 with a layer thickness of about 0.002 to 0.5 microns, for example, A1N, GaN, or Ga _m Ali N _m is used with 0 <m <. 1

Both the buffer layer 6 and the first and second coating layers 3 and 4 and the light-emitting layer 2 are preferably applied to the substrate 5 in succession by means of organometallic chemical deposition (MOCVD). After the double heterostructure 9, as shown in FIG. 1, has been formed, the second coating layer 4 and the light-emitting layer 2 are partially etched away in order to expose the first coating layer 3, as is shown in the right half of the light-emitting diode 1 from FIG. 1 you can see. An n-electrode 7 is formed on the exposed surface of the first coating layer 3, while a p-electrode 8 is formed on the surface of the second coating layer 4.

At this point it should be pointed out that the present invention does not only extend to light-emitting devices with a layer structure described with reference to FIG. 1. In particular, there are also light-emitting rende devices covered by the invention, which may have further compound semiconductor layers between the buffer layer 6 and the first coating layer 3 and / or over the second coating layer 4, in order to reduce the tension between the individual transitions of different compound semiconductors.

While the structure of a light-emitting device 1 described above with reference to FIG. 1 is already known in principle, the light-emitting device 1 according to the present invention is distinguished by a special feature which is illustrated in the enlarged section of FIG. 2.

As already mentioned above, the light-emitting devices based on gallium nitride-based compound semiconductors have very high dislocation densities. Such dislocations arise in particular due to the different lattice constants of the individual layers 2 to 6 of the devices. 2 shows an example of a dislocation 10 by an approximately vertical dashed line that extends through the two coating layers 3 and 4 and the light-emitting layer 2.

As clearly shown in FIG. 2, the thickness of the light-emitting layer 2 in the vicinity of this dislocation 10 is significantly less than in the remaining area of the light-emitting layer. The thickness in the vicinity of the offset 10 is preferably less than half the thickness of the light-emitting layer 2 in the remaining region. In the example shown in FIG. 2, a layer thickness of the light-emitting layer 2 of approximately 3 nm is selected, and the layer thickness is reduced to up to 1 nm in the vicinity of the dislocation 10.

Because of the strong piezoelectric field in the double heterostructure 9, which is particularly due to the wurtzite structure of the group III nitrides and the strongly polar nature of the If the Ga / In / Al nitrogen bond is dependent, there is a strong dependence of the effective band gap on the thickness of the light-emitting layer 2. This energy profile of the band gap over the location is shown schematically in FIG. 2 above the structure of the double heterostructure 9 , In the example shown here, at an emission wavelength of 420 nm in the light-emitting layer made of In ₀ , ιGa ₀ , ₉ N, a corresponding energy barrier is built up by increasing the effective band gap by 250 meV, which shields the dislocation.

The energy barrier constructed in this way prevents charge carriers from diffusing in the vicinity of the dislocation, as a result of which a non-radiative recombination of electron-hole pairs at dislocations can be effectively prevented. The charge carriers are thus forced to recombine in other areas of the light-emitting layer, preferably in the areas with the smallest band gaps. The diffusion of charge carriers is effectively switched off even at temperatures above room temperature.

To achieve the above energy barrier, the growth of the light-emitting layer 2 is controlled in a targeted manner when the double heterostructure 9 is formed on the substrate 5 or the buffer layer 6. By modifying the growth conditions, such as growth temperature, V / III ratio, V / V ratio, growth rate, carrier gas composition, addition of different types of surfactants (eg In, Si) and the like, dislocations 10 result from an under of the light-emitting layer 2 layer pack 3, 6 in the area of the light-emitting layer 2, to growth changes in the vicinity of such dislocations 10. These growth changes can be recognized, for example, by so-called V-defects, which are a clear indication of reduced growth rates at the point of the defect. These reduced growth rates result near dislocation 10 locally to reduced layer thicknesses of the light-emitting layer 2, as described above.

Since the method according to the invention for producing a light-emitting device based on a gallium nitride-based compound semiconductor can achieve a light-emitting device with improved luminescence yield, according to the present invention, in-free devices can also advantageously be produced with satisfactory luminescence yield.

Previous studies have shown that In-free light-emitting diodes have significantly lower luminescence yields than In-containing light-emitting diodes. The causes for this are both smaller piezoelectric fields and other growth mechanisms. It should be noted here that a light-emitting layer 2 made of InGaN is usually produced at 700-800 ° C, while temperatures above 1000 ° C are required for light-emitting layers 2 made of GaN and AlGaN. If stresses and piezoelectric fields are specifically installed in In-free light-emitting diodes, then, on the other hand, a light-emitting diode with sufficient luminescence efficiency can be achieved by specifically controlling the growth with regard to a smaller thickness of the light-emitting layers 2 in the vicinity of dislocations 10 in accordance with the present invention.

Instead of the double heterostructure 9 specifically described in connection with FIG. 2, a single or multiple InGaN / GaN quantum film structure (preferably intrinsically) is preferably provided, in which one or possibly more preferably intrinsic GaN quantum films emit as radiation - The layers are provided and the areas of reduced thickness according to the invention have near dislocations. The above illustration using the double heterostructure 9 was chosen for the sake of simplicity.

Claims

claims

1. A method for producing a light-emitting device with at least one compound semiconductor layer (2) based on gallium nitride in an active layer or active layer sequence of the device, characterized in that the growth parameters in the manufacture of the compound semiconductor layer (2) are set such that at least partially near transfers

(10) regions are produced in the compound semiconductor layer (2) in the compound semiconductor layer which have a smaller thickness than a remaining region of the compound semiconductor layer.

2nd Method according to claim 1, characterized by the method steps: forming a first coating layer (3) from a gallium nitride-based compound semiconductor of a first line type on a substrate (5);

Forming the active layer or active layer sequence with the compound semiconductor layer (2), in particular a light-emitting layer (2), over the first coating layer (3); and forming a second coating layer (4) of a gallium nitride-based compound semiconductor of a second conductivity type over the light-emitting layer (2), the composition of the gallium nitride-based compound semiconductor layer (2) being different from that of the compound semiconductor of the first and second coating layers (3, 4 ) differs.

3rd Method according to Claim 1 or 2, characterized in that the regions with a smaller thickness are at least partly less than half as thick as the remaining region of the compound semiconductor layer (2).

4. The method according to at least one of claims 1 to 3, characterized in that the compound semiconductor layer (2) from an In _x A- l _y Gaι- _x . _y N compound semiconductor with O ≤ x ≤ l, O ≤ y ≤ l and x + y ≤ 1 is formed.

5. The method according to claim 4, characterized in that x = 0.

6. The method according to at least one of claims 2 to 5, characterized in that the light-emitting layer (2) is doped with a p-type foreign substance and / or an n-type foreign substance.

7. The method according to at least one of claims 2 to 6, characterized in that the first coating layer (3) made of a Ga _u Alχ. _u N compound semiconductor with 0 <u ≤ 1 is formed.

8. The method according to at least one of claims 2 to 7, characterized in that the second coating layer (4) is formed from a Ga _v Alι_ _v N compound semiconductor with 0 <v ≤ 1.

9. The method according to at least one of claims 2 to 8, characterized in that the first coating layer (3), the compound semiconductor layer (2) and the second coating layer (4) are formed in succession by means of a MOCVD method on the substrate (5) become.

10. The method according to any one of claims 2 to 9, characterized in that a buffer layer (6) is formed on the substrate (5) before the formation of the first coating layer (3) on which the first coating layer is subsequently formed.

11. The method according to claim 10, characterized in that the buffer layer (6) from a Ga _m Al _: ι _. - _m N compound semiconductor with 0 ≤ m ≤ 1 is formed.

12. The method according to at least one of claims 2 to 11, characterized in that the substrate (5) is formed from a material which is selected from a group consisting of sapphire, silicon carbide, zinc oxide and gallium nitride.

13. The method according to at least one of claims 1 to 12, characterized in that the active layer sequence has a quantum film structure.

14. The method according to claim 13, characterized in that the quantum film structure has at least one GaN quantum film.

15. The method according to claim 14, characterized in that the quantum film structure is an InGaN / GaN quantum film structure.

16. The method according to at least one of claims 13 to 15, characterized in that the quantum film structure comprises at least one undoped GaN quantum film.

17. The method according to at least one of claims 13 to 16, characterized in that the compound semiconductor layer (2) by a GaN Quantum film or is formed by the intrinsic GaN quantum film.

18. Light-emitting device based on a gallium nitride-based compound semiconductor with an active one

Layer or layer sequence which has a compound semiconductor layer (2) based on gallium nitride, characterized in that in order to increase the quantum yield of the device, the compound semiconductor layer (2) in the vicinity of dislocations (10) has regions of less thickness than in the rest of the region.

19. The light-emitting device according to claim 18, characterized in that the compound semiconductor layer (2) is a light-emitting layer (2) which is arranged in particular between a first coating layer (3) of a first conductivity type and a second coating layer (4) of a second conductivity type is.

20. The light-emitting device according to claim 19, characterized in that the first coating layer (3) is formed from an n-type compound semiconductor based on gallium nitride, the composition of which differs from that of the compound semiconductor of the light-emitting layer; and the second coating layer (4) is formed from a p-type compound semiconductor based on gallium nitride, the composition of which differs from that of the compound semiconductor of the light-emitting layer.

21. Light-emitting device according to at least one of claims 18 to 20, characterized in that that the areas with a smaller thickness are at least partially less than half as thick as the remaining area of the compound semiconductor layer.

22. The light-emitting device according to at least one of claims 18 to 21, characterized in that the compound semiconductor layer (2) consists of an In _x A- l _y Gaι_ _x - _y N compound semiconductor with O ≤ x ≤ l, O ≤ y ≤ l and x + y ≤ 1 is formed.

23. Light-emitting device according to claim 22, characterized in that x = 0.

24. The light-emitting device according to claim 22, characterized in that 0 <x <0.5 and y = 0.

25. The light-emitting device according to at least one of claims 18 to 24, characterized in that the compound semiconductor layer (2) is doped with a p-type foreign substance and / or an n-type foreign substance.

26. Light-emitting device according to at least one of claims 19 to 25, characterized in that the first coating layer (3) made of a Ga _u Ala _. , _u N compound semiconductor is formed with 0 <u <1.

27. Light-emitting device according to one of the preceding claims 19 to 25, characterized in that the second coating layer (4) is formed from a Ga _v Alι_ _v N compound semiconductor with 0 <v ≤ 1.

28. The light-emitting device according to at least one of claims 18 to 17, characterized in that the active layer sequence has a quantum film structure.

29. The method according to claim 28, characterized in that the quantum film structure has at least one GaN quantum film.

30. The method according to claim 28, characterized in that the quantum film structure is an InGaN / GaN quantum film structure.

31. The method according to at least one of claims 28 to 30, characterized in that the quantum film structure comprises at least one intrinsic GaN quantum film.

32. The method according to at least one of claims 28 to 31, characterized in that the compound semiconductor layer (2) is formed by a GaN quantum film or by the intrinsic GaN quantum film.