JP2995186B1 - Semiconductor light emitting device - Google Patents

Abstract

An object of the present invention is to provide a device structure for realizing a light-emitting device that emits light in a short wavelength region from ultraviolet and visible light to an infrared region using a group III nitride semiconductor. SOLUTION: In the light emitting device according to the present invention, the insulating substrate is constituted by a sapphire substrate, the surface of the sapphire substrate on which a layer is to be formed is a (0001) c plane, and the first conductivity type is formed on the c plane of the sapphire substrate. A first cladding layer of a GaNSi layer of the first conductivity type is epitaxially grown through an AlN buffer layer of a single crystal. When the first cladding layer is formed, a single crystal ΔInN or (and Ga _1-x In _x N Or Al
An intrinsic active layer InN of _1-x In _x N)｝ is formed by the MOVPE method, a metal electrode is formed on the first clad layer, and a cap layer of the second conductivity type is formed on the intrinsic active layer. A of the second conductivity type with Mg added on the cap layer
An lGaN layer is formed as an optical confinement layer, and M
A second conductive type second clad layer to which g is added and a GaN layer are formed, and a metal electrode is formed on the semiconductor layer. As a result, a long-wavelength light-emitting element that does not contain toxic elements such as phosphorus and arsenic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor device comprising
The present invention relates to a high-efficiency light emitting device using a group I nitride semiconductor, and to a light emitting device used for a device such as a semiconductor laser or an LED.

[0002]

2. Description of the Related Art Conventionally, light emitting devices using a group III nitride semiconductor have been put to practical use from purple to green. The efficiency from long wavelength yellow to orange is insufficient and has not yet been put to practical use. Furthermore, there is no example realized in the long wavelength range from red to infrared, except for an example using phosphorus or arsenic as a group V element.

[0003] However, as is well known,
Source gas containing phosphorus and arsenic is dangerous because many poisonous substances
In addition, harmful substances are generated in the treatment and disposal, and there are many problems. On the other hand, nitrogen is a main component of air, and the toxicity of a raw material gas containing nitrogen, mainly ammonia, is extremely lower than that of a raw material gas containing phosphorus or arsenic. Furthermore, regarding the treatment method, it can be decomposed into non-toxic nitrogen and hydrogen by decomposition using a catalyst or the like. In other words, a light emitting device using a group III nitride semiconductor is considered including its manufacturing method.
It can be called "a semiconductor device that is friendly to the global environment." In that sense, it is strongly desired to realize a light emitting device composed only of a group III nitride semiconductor that does not contain phosphorus or arsenic.

[0004]

As described above, the nitride semiconductor material has an advantage that it is less harmful to the human body than other semiconductor materials. However, when all the semiconductor layers are made of a nitride semiconductor material, there is a disadvantage that the selection range of the semiconductor materials forming the cladding layer and the active layer is limited to an extremely narrow range. For example, a light emitting device using gallium nitride as the cladding layer and using indium nitride as the material of the active layer can obtain an appropriate long-wavelength emission wavelength. However, as shown in Table 1, the light emitting device has a gap between gallium nitride and indium nitride. There was a problem with a large lattice constant difference.

That is, for example, GaN and InN have a lattice constant difference of 11% as shown in Table 1, and the higher the fraction of InN in the active layer, the lower the lattice constant consistency. Therefore, the frequency of occurrence of defects due to dislocations increases, and it becomes difficult to produce a high-quality crystal required as an active layer. Further, the decomposition temperature of InN is lower than that of other GaN and AlN,
The fact that it is not easy to fabricate itself was also one of the reasons that application to the active layer is difficult.

[0006]

[Table 1]

Accordingly, an object of the present invention is to provide a light emitting device which emits light in the ultraviolet and visible short wavelength regions to the infrared region using a group III nitride semiconductor without using a conventional compound of phosphorus or arsenic. An object of the present invention is to realize a semiconductor light emitting device in which defects such as dislocations do not occur even when a difference in lattice constant between an active layer and a cladding layer is large, and a method for manufacturing the same.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an insulating substrate having a single crystal structure and a first conductive type GaN formed on the insulating substrate.
A first cladding layer, an active layer formed above the first cladding layer, a second cladding layer of GaN of the second conductivity type formed above the active layer, and the first and second cladding layers. A first electrode and a second electrode electrically coupled to the cladding layer, wherein the active layer is made of InN;
The thickness of the layer is equal to or less than the thickness of the layer of five molecules of InN. As described above, by configuring all the semiconductor materials constituting the device with nitride, a semiconductor light emitting device can be realized without using materials harmful to the human body.

The present inventor conducted various experiments and analyzes on the relationship between the thickness of the active layer and the luminous efficiency of the light emitting device using GaN as the cladding layer and InN as the material of the active layer. The effect of the lattice constant difference becomes smaller as the film thickness becomes smaller. According to the experiment, it was found that good luminous efficiency can be obtained when the thickness of the active layer is 2 to 5 molecules. In particular, it has been found that an extremely good luminous efficiency can be obtained in the case of a five-molecule layer, and the luminous efficiency sharply decreases when the number of the five-molecular layer is exceeded. From such a viewpoint, in the present invention, the thickness of the active layer is set to be equal to or less than the thickness of five molecular layers of InNN, and the problem of the lattice constant difference is solved.

Further, the present inventor conducted various experiments on the relationship between the growth temperature of the active layer and the luminous efficiency.
It turns out that there is an important relationship. That is, 300 °
If InN is grown at a temperature below C, the luminous efficiency will be significantly reduced. On the other hand, at a temperature of 700 ° C. or more, InN
It has been found that growing a high-quality InN film cannot grow a high-quality InN film. From this experimental result, in the present invention, the active layer is grown in a temperature range of 300 to 700 ° C.

As for the problem caused by the relatively low decomposition temperature of InN, the decomposition of the active layer is suppressed by growing an InN active layer and then depositing a GaN cap layer thereon. be able to.

The present invention is applicable not only to light emitting semiconductor devices such as semiconductor lasers and LEDs, but also to various semiconductor devices such as solar cells and optical sensors which are formed by laminating a metal layer or a semiconductor layer on an insulating substrate. Can also be applied. As a method for epitaxially growing a semiconductor layer, metal organic chemical vapor deposition, liquid phase epitaxial growth,
Various epitaxial growth methods such as a vapor phase epitaxial growth method and a molecular beam epitaxial manufacturing method can be used.

For forming an electrode, a part of the p-type layer and the active layer is removed by reactive ion etching to expose an n-type layer on the surface, and a low work function metal such as Ti or Al is deposited. Thus, an n-type electrode can be manufactured, and a positive electrode can be manufactured by depositing a high work function metal such as Au, Pt, or Ni on a p-type layer.

Although the above-mentioned two electrodes are deposited by a sputtering process, the metal to be an electrode is deposited by an epitaxial growth in a more thermally stable state in an equilibrium state such as liquid phase epitaxy. Deposition methods can also be used.

A sapphire substrate can be used as a single crystal substrate.
A first (n-type in this case) GaN layer is provided between
It is advantageous to interpose a conductive type buffer layer. As the buffer layer, for example, a first conductivity type (in this example, n-type) A in which the substrate is heated to around 1000 ° C. and a small amount of Si is added.
InN can be grown by 5 nm. As a material of the buffer layer, a material having a small lattice constant difference from the GaN layer deposited on the upper side is preferable.

In a preferred embodiment of the method according to the present invention, the metalorganic vapor phase epitaxy step involves the use of ΔInN or (Ga
_{A 1-x} In _x N or Al _1-x In _x N)｝ layer was grown on several molecular layers n-type GaN. As a result of performing various experiments on this growth process, when binary InN was grown, deposition was performed by metal organic chemical vapor deposition while maintaining the substrate in a temperature range of 300 ° C. to 700 ° C. It has been found that a genuine active layer that has been successfully epitaxially grown can be formed. This is because if the substrate temperature is lower than that, InN with low luminous efficiency grows, and if the substrate temperature is higher than that, InN does not grow. In the case of depositing binary InN, the efficiency was highest when the film thickness was 2 to 3 molecular layers.

The ternary ｛InN or (Ga _{1 -x} In _x N)
Alternatively, in the case of Al _1-x In _x N (where X is 0.5 or more)), the higher the fraction of GaN and InN, the more the luminous efficiency tends to be maximized with a larger number of molecular layers, Ga
_{For both 0.5} In _0.5 N and Al _0.5 In _0.5 N, the luminous efficiency was maximized when the number of molecular layers was 5, and when the thickness was larger than this, the luminous efficiency sharply decreased.

[0018]

FIG. 1 is a schematic sectional view showing the structure of a light emitting device according to the present invention. In this example, a case will be described in which a layer structure for manufacturing a light emitting element using InN as a base material of an active layer is formed. A sapphire substrate 10 having a single crystal structure is used as an insulating substrate. This sapphire substrate 10 has a surface 1 on which a layer structure is to be formed.
A first cladding layer of GaN of the first conductivity type (n-type in this case), an active layer and a second cladding of the second conductivity type (p-type in this case) on the surface 10a. The layers are formed sequentially. In this example, the surface 10 on which the layer structure is to be formed is
The (0001) c plane is used as a. The surface 10a of the sapphire substrate 10 on which a layer is to be formed may be a normal mirror-polished surface or a flat surface that has been subjected to a super-flattening process by a high-temperature annealing process. Can be.

First, after setting a sapphire substrate on a susceptor in a reaction tube, the substrate temperature is set to about 1000 in a hydrogen stream.
C. for several minutes to clean the substrate surface. Next, the temperature of the substrate is lowered, and the c-plane of the sapphire substrate is used as a surface on which a layer structure is to be formed, and a buffer layer 11 of AlN is deposited on this surface by several tens nm. In this example, a buffer layer is deposited by the MOCVD method, and the AlN layer 11 having a uniform crystal orientation is formed.

Next, a first cladding layer 12 of GaN of the first conductivity type to which Si is added is epitaxially grown on the buffer layer 11. In this case, the substrate 10 is 1000
It is preferable to raise the temperature to around ℃. The first cladding layer 12 of n-type GaN to which Si is added is 3 × 10 ¹⁸
(Atoms / cm ³ ) and 5 μm.

Next, the temperature of the substrate is lowered to form an active layer 13 of {InN or (Ga _{1 -x} In _x N or Al _{1 -x} In _x N)} of several molecular layers of the first conductivity type (in this case, n Ga)
It was deposited on the N semiconductor 12 by an organic metal compound vapor phase epitaxy apparatus. FIG. 2 is a schematic view of a crystal growth apparatus used for manufacturing a semiconductor light emitting device according to the present invention. In this step, trimethyl gallium (TMG) trimethyl aluminum (TMA), trimethyl indium (TMI)
And ammonia.

Regarding the preparation of the active layer, in the embodiment according to the present invention, the active layer material is made of binary (InN) and ternary (Ga _1-x In _x N or Al _1-x In _x N)}. An experiment was performed on the case.

First, when growing binary InN, while maintaining the substrate temperature in the range of 300 ° C. to 700 ° C., the InN layer is formed of several molecular layers of the first conductivity type (in the case of this example). Was grown on n-type) GaN. As a result of conducting various experiments on this growth process, it was found that when deposition was performed by metal organic chemical vapor deposition while maintaining the substrate at a temperature in the range of 300 ° C. to 700 ° C., a well-epitaxially grown active layer could be formed. Was. This is because if the substrate temperature is lower than that, InN with low luminous efficiency grows, and if the substrate temperature is higher than that, InN does not grow. Also,
In the case of depositing binary InN, the efficiency was highest when the film thickness was 2 to 3 molecular layers.

[0024] Second, when ternary (Ga _1-x In x N or Al _1-x In x N (where X is 0.5 or more)) to grow in, (Ga _1-x In x N or Al _1-x In _x
A layer of N (where X is 0.5 or more) was deposited by metal organic chemical vapor deposition, and the higher the fraction of GaN and AlN, the higher the substrate temperature. This is because the decomposition temperature of GaN and AlN is higher than the decomposition temperature of InN. In addition, as for the layer thickness, the higher the fraction of GaN and AlN, the more the luminous efficiency tends to be maximized with a larger number of molecular layers, and Ga _0.5 In _0.5 N or Al _0.5 In _0.5 N
In each case, the luminous efficiency was maximized with 5 molecular layers.

After the active layer 13 is formed, the second conductive type (p-type in this example) Ga is used to prevent the active layer 13 from being decomposed.
An N cap layer 14 is formed on the active layer 13, and Mg is added on the cap layer 14 as a light confinement layer.
A conductive AlGaN layer 15 is epitaxially grown to a thickness of 0.1 nm at 1 × 10 ¹⁸ (atoms / cm ³ ).
Second conductivity type GaN doped with Mg on lGaN layer 15
The second cladding layer 16 was formed at 5 × 10 ¹⁷ (atoms / cm ³ ) by a 0.5 nm epitaxial growth method.

Finally, the second ion is formed by reactive ion etching.
Layer 16, optical confinement layer 15, cap layer 1
4. The active layer 13 and a part of the first clad layer 12 are removed to expose a part of the first clad layer 12, and a negative electrode 18 is formed on the first clad layer 12 as a negative electrode 18.
i, a low work function metal such as Al is deposited, and Au, P is formed on the second cladding layer as a positive electrode 17.
High work function metals such as t and Ni were formed by vapor deposition. These two electrodes 17, 18 were deposited by a sputtering process.

Next, the characteristics of the semiconductor light emitting device manufactured as described above will be described. When the light emitting device according to the present invention was driven by applying a direct current so that the P-type layer was positive and the N-type layer was negative, light emission was observed from around 2.5 V,
At a voltage of 3 V and a current of 20 mA, strong light emission similar to that of PL was observed. As a result, it has been demonstrated that ultraviolet or visible short-wavelength and infrared light emission, which has conventionally been difficult with a group III nitride semiconductor, is possible.

FIG. 3 shows a photoluminescence spectrum (PL) at room temperature when two molecular layers of InN (lower figure) and three molecular layers (upper figure) are used as the active layer. A strong PL of purple was observed with a molecular number of 2 and a bluish green with a molecular number of 3. InN has a band gap of 1.9 eV in red, but actual light emission has higher photon energy. This is thought to be due to the quantum size effect or the deformation potential.

According to the present invention, a light emitting element free of toxic elements such as phosphorus and arsenic can be obtained. The embodiments of the present invention are only specific examples, do not limit the scope of the present invention, and are clearly improved by those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a light emitting device manufactured according to the present invention.

FIG. 2 is a schematic view of a crystal growth apparatus used for manufacturing a semiconductor light emitting device according to the present invention.

FIG. 3 shows a photoluminescence spectrum (PL) at room temperature in the case of using two molecular layers (lower figure) and three molecular layers (upper figure) of InN as an active layer produced according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 sapphire (0001) substrate 10a (0001) c-plane to be formed layer 11 AlN buffer layer 12 n-type GaN layer added with Si 13 active layer according to the present invention 14 cap layer 15 p-type AlGaN layer added with Mg 16 p-type GaN layer doped with Mg 17 p-electrode 18 n-electrode

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Amano 2-104 Yamanote, Naito-ku, Nagoya-shi, Aichi 508 Takara Mansion Yamanote 508 (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 33/00 H01S 3 / 18

Claims (5)

(57) [Claims] 1. An insulating substrate having a single crystal structure, a first cladding layer of GaN of a first conductivity type formed above the insulating substrate, and an active layer formed above the first cladding layer. And a second conductivity type Ga formed above the active layer.
A second cladding layer of N, and first and second electrodes electrically coupled to the first and second cladding layers, respectively, wherein the active layer is made of InN; A semiconductor light-emitting device, wherein the thickness is equal to or less than the thickness of a layer of five molecules of InN. 2. A cap layer of a second conductivity type GaN for suppressing the decomposition of InN in the active layer is interposed between the active layer and the second cladding layer. 3. The semiconductor light emitting device according to item 1. 3. The semiconductor light emitting device according to claim 2, wherein an AlGaAs light confinement layer is interposed between the cap layer and the second cladding layer. 4. An insulating substrate having a single crystal structure, a first cladding layer of GaN of a first conductivity type formed above the insulating substrate, and an In layer formed above the first cladding layer.
An active layer of N, a second cladding layer of GaN of a second conductivity type formed above the active layer, and first and second electrically conductive layers respectively coupled to the first and second cladding layers. In manufacturing a semiconductor light-emitting device having the above-mentioned electrodes, the active layer is formed by metalorganic vapor phase epitaxy at 300 to 700 °.
A method for manufacturing a semiconductor light emitting device, wherein the semiconductor light emitting device is grown in a temperature range of C. 5. The method according to claim 4, wherein the thickness of the active layer is equal to or less than the thickness of a layer of five molecules of InN.