JP3972943B2 - Gallium nitride compound semiconductor light emitting device - Google Patents

Description

The present invention relates to a gallium nitride-based compound semiconductor (In _a Al _b Ga _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦) used in a light emitting element such as a laser diode (LD) or a light emitting diode (LED). 1) It is related with the light emitting element which consists of.

A blue LED having a light intensity of 1 cd that is currently in practical use is composed of a gallium nitride compound semiconductor (In _a Al _b Ga _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1), and is shown in FIG. It has a structure. That is, on the surface of a substrate 1 made of sapphire, a buffer layer 2 made of GaN, an n-type layer 3 made of GaN, an n-type cladding layer 4 made of AlGaN, an active layer 5 made of InGaN, and a p-type made of AlGaN. This is a double hetero structure in which a type cladding layer 6 and a p-type contact layer 7 made of GaN are sequentially laminated. This blue LED shows the highest performance of a blue LED, with a forward current (If) of 20 mA, a forward voltage (Vf) of 3.6 V, a peak emission wavelength of 450 nm, a luminous intensity of 1 cd, and an emission output of 1.2 mW.

  In the LED having the structure described above, the substrate 1 can be made of materials such as ZnO, SiC, GaAs, and Si in addition to sapphire, but sapphire is generally used. In addition to GaN, the buffer layer 2 is formed of GaAlN, AlN, or the like. The n-type contact layer 3 and the n-type cladding layer 4 are formed of a gallium nitride compound semiconductor obtained by doping a gallium nitride compound semiconductor with an n-type dopant such as Si, Ge, Sn, or C. Further, the n-type contact layer 3 and the n-type clad layer 4 may be made to act as a clad layer and a contact layer as a single n-type layer without being divided into two layers in this way (that is, any one of them) Layer can be omitted). The active layer 5 is made of a gallium nitride compound semiconductor containing at least indium, and is doped with a non-doped, p-type dopant such as Zn, Mg, Cd, or Be and / or an n-type dopant. The p-type cladding layer 6 and the p-type contact layer 7 are made p-type by doping a gallium nitride compound semiconductor with a p-type dopant and then annealing at 400 ° C. or higher. Further, the p-type cladding layer 6 and the p-type contact layer 7 may act as a clad layer and a contact layer as a single p-type layer (any layer may be omitted as in the case of the n layer).

  In the case of a gallium nitride-based compound semiconductor, the current generally has a property that it is difficult to spread uniformly compared to other III-V group compound semiconductors such as GaAs, GaP, and AlInGaP. Therefore, when the LED element having the structure as shown in FIG. 1 is realized, there is a problem that the flow of electrons supplied from the n layer to the active layer is concentrated on a portion having a low resistance. FIG. 2 schematically shows light emission of the active layer due to current concentration. This is because electrons supplied from the negative electrode 8 of the n-type contact layer 3 are formed between the positive electrode 9 of the p-type contact layer 7 and the negative electrode 8 of the n-type contact layer 3 as shown by arrows in FIG. It indicates that the active layer 5 emits light strongly as shown by the shaded portion by flowing the closest distance so that the resistance between them is low. As described above, there is a drawback that uniform light emission cannot be obtained from the active layer 5 unless the electrons spread uniformly in the n-type contact layer 3.

  Further, the LED having the above structure has Vf of 3.6 V, which is 5 V or more lower than the blue LED made of the conventional MIS structure gallium nitride compound semiconductor. This indicates light emission by the pn junction, but there is still room for improvement with respect to Vf, and further reduction of Vf is desired.

  Accordingly, the present invention has been made in view of such circumstances, and its object is to have a structure in which at least an n-type layer is formed between the active layer and the substrate, such as a double hetero, a single hetero, etc. In the gallium nitride-based compound semiconductor light-emitting device, the first is to obtain uniform light emission from the active layer, to improve the luminous intensity and output of the device, and the second is to further reduce the Vf, thereby improving the luminous efficiency. It is to improve.

We have found that the above problem can be solved by interposing a layer having a higher carrier concentration in the n-type layer. That is, the gallium nitride compound semiconductor light emitting device of the present invention has a structure in which an n-type layer, an active layer, and a p-type layer are stacked on a substrate, and a surface on which the n-type layer is partially exposed. And a first n-type layer in contact with the first n-type layer and the first n-type layer in the n-type layer. And an electron supplied from an electrode formed on the exposed n-type layer surface in parallel in the second n-type layer. A gallium nitride compound semiconductor light-emitting element that is supplied or moved.

  As described above, all the light-emitting elements of the present invention can obtain a uniform light emission from the active layer to improve the light emission output. In addition, in the light emitting element in which the second n-type layer 33 is formed between the negative electrode 8 and the substrate 1 as in Examples 1 and 2, Vf is clearly reduced. In Example 3, since the second n-type layer is not between the substrate and the negative electrode, Vf has little influence on the decrease, but since the second n-type layer is a multilayer film, the active layer, p The crystal defects in the type cladding layer and the p-type contact layer are reduced, and the light emission output is improved. As described above, the light emitting device of the present invention has the second n-type layer having a high carrier concentration formed on the active layer side in contact with the first n-type layer, thereby obtaining uniform surface light emission and light emission output. An improved element can be realized.

  FIG. 3 shows the structure of a light emitting device according to an embodiment of the present invention. The basic structure is almost the same as that of the light emitting device shown in FIG. 1, but in contact with the n-type contact layer 3 which is the first n-type layer, the active layer 5 side is closer to the first n-type layer 3 than the first n-type layer 3. A new second n-type layer 33 having a high electron carrier concentration is formed. The substrate 1, the buffer layer 2, the n-type contact layer 3, the n-type cladding layer 4, the active layer 5, the p-type cladding layer 6, the p-type contact layer 7, etc. are formed of a gallium nitride compound semiconductor, and the n-type contact layer 3 And the n-type cladding layer 4 may be a single n-type layer, and the p-type cladding layer 6 and the p-type contact layer 7 may be a single p-type layer.

  In the light emitting device of the present invention, in order to grow a gallium nitride-based compound semiconductor layer having excellent crystallinity, sapphire is preferably used for the substrate 1 and GaN or AlN is grown on the buffer layer 2 so that the thickness ranges from 10 Å to 0.5 μm. It is preferable to form with the film thickness.

  The first n-type layer formed between the active layer 5 and the substrate 1 is usually formed with a thickness of 1 μm to 5 μm as the n-type contact layer 3, and the n-type cladding layer 4 is formed on the surface thereof. The film is grown to a thickness of 50 Å to 1 μm. However, as described above, the n-type cladding layer 4 need not be formed. As the gallium nitride compound semiconductor, GaN and AlGaN are preferable, and GaN is most preferable. This is because GaN and AlGaN easily become n-type by non-doping or doping with an n-type dopant, and the electron carrier concentration can be easily controlled by the dopant. Furthermore, GaN tends to grow in order to form a thick film having a single layer and better crystallinity than AlGaN. For example, when an element in which an n-type layer and a p-type layer are sequentially stacked using sapphire as a substrate is realized, the electrode 8 of the n-type contact layer 3 is provided, so that the p-type layer is removed by etching and the n-type contact layer 3 is removed. Although it is necessary to expose it, if a thick film can be formed with a single layer, there is a degree of freedom in etching depth, which is very convenient in realizing an actual device.

  Next, the active layer 5 is preferably grown to a thickness of usually 50 Å to 0.5 μm, and is preferably InGaN. InGaN can easily change the emission wavelength of the light-emitting element from purple to green using interband light emission based on the mixed crystal ratio of indium, and can also be doped with n-type and p-type dopants to be the emission center. Is also easy. Furthermore, the mixed crystal ratio (In / Ga) of In to Ga is preferably 0.5 or less. Since more than 0.5 InGaN has poor crystallinity, it tends to be difficult to obtain a practical light emitting device. As the most excellent active layer, an n-type dopant and a p-type dopant are doped to form an n-type, and InGaN having an In mixed crystal ratio of 0.5 or less to Ga is preferably used as the active layer.

  The p-type layer grown on the active layer 5 is also preferably GaN or AlGaN, the p-type cladding layer 6 is formed with a thickness of 50 angstroms to 1 μm, and the p contact layer 7 is grown with a thickness of 50 angstroms to 5 μm. . However, the p-type cladding layer 6 need not be particularly formed. As the gallium nitride compound semiconductor, GaN and AlGaN are preferably formed. These are easy to grow a thick film with a single layer and good crystallinity. Further, when doped with a p-type dopant and annealed at 400 ° C. or higher, the p-type is easily formed. Tend to be.

[Action]
FIG. 4 schematically shows the flow of electrons supplied from the n-type contact layer 3, which is the first n-type layer in the light emitting device of FIG. 3, to the active layer 5. This is because the electrons supplied from the n-type contact layer 3 uniformly spread through the second n-type layer 33 having a high electron carrier concentration as indicated by the arrows, thereby causing the active layer 5 to emit light uniformly. Is shown. When the second n-type layer 33 having a higher electron carrier concentration than the first n-type layer is formed on the active layer side in contact with the first n-type layer in this way, electrons are transferred to the second n-type layer. Since the active layer 5 spreads uniformly in the active layer 5, uniform surface emission can be obtained.

The second n-type layer 33 is preferably In _X Al _Y Ga _1- XYN (0 <X, Y ≦ 0) containing indium, and particularly preferably a mixed crystal ratio of In to Ga (In / Ga) is preferably 0.5 or less InGaN. This is because the gallium nitride compound semiconductor containing In is easier to form a layer having a higher electron carrier concentration than the one containing no In, and the crystal containing In is softer than the crystal containing no In, such as dislocation. Easy to absorb crystal defects. Therefore, when the first n-type layer 3 such as AlGaN, GaN or the like that is not lattice-matched is grown on the substrate, the second n-type layer 33 relaxes the crystal defects of the first n-type layer 3. This is because it is possible.

The electron carrier concentration of the second n-type layer 33 is preferably adjusted to a range of 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²² / cm ³ , and the electron carrier concentration is higher than that of the second n-type layer 33. The small first n-type layer is preferably adjusted to a range of 1 × 10 ¹⁶ / cm ³ to 1 × 10 ¹⁹ / cm ³ . These electron carrier concentrations can be adjusted by doping the second n-type layer with an n-type dopant such as Si, Ge, Sn, or C as described above. If the electron carrier concentration of the second n-type layer 33 is lower than 1 × 10 ¹⁸ / cm ^3, it is difficult to obtain the function of spreading electrons, and it is difficult to obtain uniform light emission of the active layer, 1 × 10 ²² / cm. ^When it is larger than ³ , the crystallinity is deteriorated, and the performance of the light emitting element may be adversely affected. The first n-type layer also has a thickness of 1 μm or more when the electron carrier concentration is less than 1 × 10 ¹⁶ / cm ^{3, and} it is difficult to obtain light emission of the active layer itself, and when it is greater than 1 × 10 ¹⁹ / cm ^3. This is because the crystallinity tends to deteriorate when the film is formed, and the output of the element may be reduced.

  The film thickness of the second n-type layer 33 is usually 10 angstroms to 1 μm, more preferably 50 angstroms to 0.3 μm. If it is thinner than 10 angstroms, the crystallinity becomes insufficient, so that it is difficult to obtain the function of spreading electrons, and it is difficult to obtain uniform light emission of the active layer. This is likely to occur inside and the crystallinity is deteriorated, so that the performance of the light emitting element may be deteriorated.

  Further, the second n-type layer 33 may be a multilayer film in which two or more gallium nitride compound semiconductors having different composition ratios of In, Ga, and Al are stacked. The thickness of each layer in forming the multilayer film is preferably 10 Å to 1 μm, more preferably 50 Å to 0.3 μm. By forming the second n-type layer 33 as a multilayer film, the crystal defects in the first n-type layer are stopped by the multilayer film layer, and the gallium nitride compound semiconductor that is not lattice-matched is stacked. Therefore, the output of the light-emitting element can be improved because a semiconductor layer having excellent crystallinity can be grown.

  Next, FIG. 5 is a schematic cross-sectional view showing the structure of a light emitting device of another embodiment of the present invention. This is because a second n-type layer 33 is formed between the negative electrode 8 formed on the first n-type layer 3 and the substrate 1, and the distance between the second n-type layer 33 and the negative electrode 8 is Indicates that you are approaching. Originally, if the electrode 8 can be formed on the surface of the second n-type layer 33 having a high carrier concentration, for example, electrons flow through the second n-type layer 33 having a high carrier concentration as compared with FIG. Therefore, Vf of the light emitting element can be reduced. However, when an insulating substrate such as sapphire is used, it is difficult to stop the etching with the second n-type layer 33 in terms of production technology. Therefore, the second n-type layer 33 and the negative electrode as shown in FIG. 8 is shortened, and electrons injected from the electrode 8 pass through the second n-type layer 33 having a high carrier concentration, whereby Vf can be lowered.

  Furthermore, the sapphire is used as a substrate, and at least an n-type layer, an active layer, and a p-type layer are sequentially stacked on the surface of the sapphire substrate, and the p-type layer and the active layer are etched and exposed. In a light emitting device having a structure in which an electrode is formed on the surface of the layer, Vf can be effectively reduced by forming the second n-type layer 33 between the electrode formation surface of the n-type layer and the substrate. Can do. This is because if the light emitting device has a structure in which a gallium nitride compound semiconductor is grown on the surface of a conductive substrate such as SiC, ZnO, or Si, the n-type layer electrode can be formed on the substrate side, and the n-layer side electrons are active. Supplied perpendicular to the layer. On the other hand, the element having the sapphire substrate as described above is supplied in parallel to the active layer. The distance that vertically supplied electrons move through the n-type layer is at most several μm, whereas the distance of electrons supplied in parallel is several tens to several hundreds of μm. Therefore, in the element in which electrons are supplied in parallel, increasing the carrier concentration of the second n-type layer to which electrons are supplied in parallel makes it easier for the electrons to move, so that Vf can be lowered.

A buffer layer 2 made of GaN is grown to a thickness of 0.02 μm on the surface of the substrate 1 made of sapphire having a diameter of 2 inches by the MOVPE method. This surface of the buffer layer 2 as the first n-type layer, the n-type contact layer 3 made of n-type GaN electron carrier concentration of 5 × ^10/18 cm ³ doped with Si is grown to the thickness of 1 [mu] m.

Next, as a second n-type layer on the surface of the n-type contact layer 3, an n-type In0.1Ga0.9N layer doped with Si and having an electron carrier concentration of 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.05 μm. Let

Next, an n-type contact layer 3 ′ made of GaN having an electron carrier concentration of 5 × 10 ¹⁸ / cm ³ doped with Si is grown to a thickness of 3 μm.

On the surface of the n-type contact layer 3 ′, an n-type clad layer made of n-type Al0.2Ga0.8N having an electron carrier concentration of 1 × 10 ¹⁸ / cm ³ doped with Si is grown to a thickness of 0.1 μm. An active layer 5 made of Si and Zn-doped n-type In0.1Ga0.9N is 0.1 μm, a p-type cladding layer 6 made of Mg-doped Al0.2Ga0.8N, and a p-type contact layer 7 made of Mg-doped GaN. Are sequentially grown and stacked.

  The wafer obtained as described above is put in an annealing apparatus and annealed at 700 ° C. to make the p-type cladding layer 6 and the p-type contact layer 7 have a lower resistance p-type, and then the surface of the p-type contact layer 7. Then, a mask having a predetermined shape is formed, and etching is performed from the p-type contact layer side to expose the n-type contact layer 3 ′.

  Thereafter, according to a conventional method, a positive electrode 9 is formed on the p-type contact layer 7 and a negative electrode 8 is formed on the exposed n-type contact layer 3 ′, and then separated into chips to obtain a blue structure having a structure as shown in FIG. A light emitting element was obtained. When this light emitting device was made to emit light, uniform surface emission with a main emission wavelength of 450 nm was observed from the active layer 5, Vf was 3.3 V, and the light emission output was 1.8 mW at a forward current (If) of 20 mA. It was.

An n-type contact layer 3 made of Ge-doped GaN having an electron carrier concentration of 1 × 10 ¹⁸ / cm ³ is grown as a first n-type layer on the surface of the buffer layer 2 to a thickness of 1 μm, and an electron carrier concentration is formed on the surface. A second n-type layer made of 5 × 10 ²⁰ / cm ³ Ge-doped In 0.2 Ga 0.8 N is grown at a film pressure of 0.01 μm. Next, on the surface of the second n-type layer 33, an n-type contact layer 3 ′ made of Ge-doped n-type GaN having an electron carrier concentration of 1 × 10 ¹⁸ / cm ³ is set to 2 μm, and the electron carrier concentration is 5 × 10 ²⁰ / cm. ³ μm of the second n-type layer 33 ′ made of ³ Ge-doped n-type In 0.2 Ga 0.8 N and 1 μm of the Ge-doped n-type GaN layer having an electron carrier concentration of 1 × 10 ¹⁸ / cm ³ Grow in order.

  Thereafter, the n-type cladding layer 4, the active layer 5, the p-type cladding layer 6 and the p-type contact layer 7 were laminated in the same manner as in Example 1 to obtain a blue light emitting device having a structure as shown in FIG. However, as shown in FIG. 6, the etching depth from the p-type contact layer 7 is up to the n-type contact layer 3 ', and the negative electrode 8 is formed on the surface of the n-type contact layer 3'. When this light emitting device was caused to emit light, uniform surface light emission was observed from the active layer 5 as in Example 1, Vf of 3.2 V at If20 mA, and light emission output of 2.0 mW.

On the surface of the buffer layer 2, an n-type contact layer 3 made of Si-doped Al0.1Ga0.9N having an electron carrier concentration of 1 × 10 ¹⁸ / cm ³ is grown as a first n-type layer to a thickness of 3 μm. Then on the surface thereof, and 0.01μm Si-doped In0.2Ga0.8N the electron carrier concentration 1 × ^{10 20} / cm ^3, a Si-doped Al0.05Ga0.95N electron carrier concentration 1 × ^{10 20} / cm ³ 0 A second n-type layer 33 in which five layers of 0.01 m are alternately stacked is grown.

Next, on the surface of the second n-type layer 33, an active layer 5 made of Si and Zn-doped n-type In0.1Ga0.9N is 0.1 .mu.m, and a p-type cladding layer 6 made of Mg-doped Al0.2Ga0.8N. Then, a p-type contact layer 7 made of Mg-doped GaN is sequentially grown and laminated. That is, the active layer 5, the p-type cladding layer 6, and the p-type contact layer 7 are grown in the same manner except that the n-type cladding layer 4 of Example 1 is not grown. Thereafter, etching was performed in the same manner as in Example 1 to obtain a light emitting device having a structure as shown in FIG. When this light emitting device was caused to emit light, uniform surface light emission was obtained from the active layer 5 in the same manner. At If20 mA, Vf was 3.5 V, and the light emission output was 2.2 mW.
[Comparative Example 1]

  The light emitting device having the structure shown in FIG. 1 was obtained in the same manner as in Example 1 except that the second n-type layer 33 was not grown and the GaN contact layer was continuously grown to a thickness of 4 μm. The active layer of this light emitting element emitted strong light between the positive electrode 9 and the negative electrode 8 as shown in FIG. 2, and uniform light emission could not be obtained. Further, at If20 mA, Vf was 3.6 V and the light emission output was 1.2 mW.

The present invention relates to a gallium nitride-based compound semiconductor (In _a Al _b Ga _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦) used in a light emitting element such as a laser diode (LD) or a light emitting diode (LED). 1) It is related with the light emitting element which consists of.

FIG. 6 is a schematic cross-sectional view illustrating a structure of a conventional light emitting element. FIG. 2 is a schematic cross-sectional view illustrating a light emitting state of the light emitting element of FIG. 1. 1 is a schematic cross-sectional view illustrating a structure of a light-emitting element according to an embodiment of the present invention. FIG. 4 is a schematic cross-sectional view illustrating a light emission state of the light emitting element of FIG. 3. The schematic cross section which shows the light emission state of the light emitting element of the other Example of this invention. The schematic cross section which shows the structure of the light emitting element of the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 4 ... n-type cladding layer 5 ... Active layer 6 ... p-type cladding layer 7 ... p Type contact layer 8 ... negative electrode 9 ... positive electrode 3, 3 ', 3 "... first n-type layer (n-type contact layer)
33, 33 '... the second n-type layer

Claims (6)

A structure in which an n-type layer, an active layer, and a p-type layer are stacked on a substrate is provided, and a positive electrode and a negative electrode are provided on the p-type layer and on a surface where the n-type layer is partially exposed, respectively. A gallium nitride compound semiconductor light emitting device,
The n-type layer has a first n-type layer and a second n-type layer in contact with the first n-type layer and having a higher electron carrier concentration than the first n-type layer,
In the n-type layer region between the active layer in the n-type layer and the exposed surface,
The first n-type layer, the second n-type layer provided on the active layer side of the first n-type layer, and the first n-type layer on the active layer side of the second n-type layer A gallium nitride-based compound semiconductor light-emitting element having a mold layer and an n-type cladding layer on the first n-type layer. A structure in which an n-type layer, an active layer, and a p-type layer are stacked on a substrate is provided, and a positive electrode and a negative electrode are provided on the p-type layer and on a surface where the n-type layer is partially exposed, respectively. A gallium nitride compound semiconductor light emitting device,
The n-type layer has a first n-type layer and a second n-type layer in contact with the first n-type layer and having a higher electron carrier concentration than the first n-type layer,
In the n-type layer region between the substrate in the n-type layer and the exposed surface,
The first and n-type layer, a second n-type layer and, a gallium nitride-based compound semiconductor light-emitting device that have a provided on the substrate side of said first n-type layer. Wherein the n-type layer region, the second contact under the n-type layer, a first n-type layer further comprises claim 1 or gallium nitride-based compound 2, wherein the semiconductor light emitting element. The first n-type layer and the second n-type layer are a first n-type layer, a second n-type layer, a first n-type layer, a second n-type layer, and a first n-type layer. 4. The structure according to any one of claims 1 to 3 , wherein the two second n-type layers are provided on the active layer side and the substrate side from the exposed surface of the negative electrode, respectively. The gallium nitride-based compound semiconductor light-emitting device according to Item. 5. The nitride semiconductor light emitting device according to claim 1, wherein the second n-type layer has a thickness of 10 Å to 1 μm. The nitride semiconductor light-emitting element according to claim 1, wherein the first n-type layer is GaN or AlGaN.

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