JPH0923026A - Iii-v compound semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element which can highly efficiently emit light by utilizing band-end emission. SOLUTION: A light emitting element is constituted by laminating a compound semiconductor containing at least two layers having different band gaps and expressed by a general expression of Inx Gay Alz N (where, x+y+z=1, 0<=x<=1, 0<=y<=1, and 0<=z<=1) upon a sapphire substrate. The angle between the surface and C-plane of the sapphire substrate is adjusted to 5 deg. so that band end emission can be utilized.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the general formula In _x Ga _y
Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦
The present invention relates to a light emitting device using a 3-5 group compound semiconductor represented by y ≦ 1, 0 ≦ z ≦ 1).

[0002]

2. Description of the Related Art Ultraviolet or blue light emitting diodes (hereinafter
Below, it may be described as LED. ) Or ultraviolet or blue
Generally used as a material for light-emitting devices such as laser diodes for color
Formula In _xGa_yAl_zN (however, x + y + z = 1,0
≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) 3-5
Group compound semiconductors are known. Especially InN in mixed crystal ratio
Those containing 10% or more emit in the visible region depending on the In concentration.
It is particularly important for display applications because it can adjust the light wavelength.
The group 3-5 compound semiconductor is sapphire, GaAs, Zn
Attempts have been made to form films on various substrates such as O.
You. Especially sapphire has a large area and high quality single crystal
It is important because it can be easily manufactured. Sapphire substrate
Regarding plane orientation, studies using A-plane, R-plane, C-plane, etc. have been conducted.
It is comparatively good by using the C surface among them.
It is known that such a compound semiconductor can be obtained. Nitriding
Light emitting device using impurity light emission of gallium compound semiconductor
The compound semiconductor from the C-plane of the sapphire substrate
By growing on a substrate (off-substrate) tilted by a few degrees
The non-specular surface improves the extraction efficiency and improves the external quantum effect.
There is a report that the efficiency (luminous efficiency) can be improved.
6-291368). Also, in general, such as GaAs
Low index such as (001) and (111) in crystal growth
A GaAs substrate with a plane orientation is used, but in reality
Some angle from these planes (hereinafter referred to as off angle)
is there. ) Good quality is obtained by using a substrate with an inclined surface.
Crystals may be obtained.

Here, the light emitting mechanism of the LED can be roughly classified into two. One is a mechanism in which the injected electrons and holes are recombined via the level formed by impurities in the band gap, which is generally called impurity emission. On the other hand, the injected electrons and holes are recombined without passing through the levels due to impurities, and in this case, light emission at a wavelength substantially corresponding to the band gap can be obtained. This is called band edge emission. In the case of impurity emission, the emission spectrum is generally broad. On the other hand, band-edge emission has a sharp emission spectrum, and band-edge emission is preferable when high color purity is required. In addition, since the recombination of electrons and holes through the impurity levels is used in impurity emission, a sufficient number of impurity levels are required to trap the injected electrons or holes, but in general, high impurity levels are required. If doped to a high concentration, the crystal quality will deteriorate. That is, the number of impurity levels that can be formed in a high quality crystal is limited. In this case, as the injection amount of electrons and holes increases, the number of impurity levels becomes insufficient, and the recombination of electrons and holes does not occur via the impurity levels. That is, the luminous efficiency is reduced at a high current. On the other hand, in the case of band edge light emission, light emission that does not go through the impurity level is used, and thus such reduction in light emission efficiency does not occur. Therefore, band edge emission is preferred when high current injection is required. On the other hand, the compound semiconductor has a direct transition type bandgap, and the bandgap can be set in the visible region by its composition. Therefore, by using this layer as a light emitting layer, a highly efficient light emitting element by band edge emission can be manufactured without using impurity light emission. With band edge emission, the emission power can be concentrated in a narrow wavelength range, the emission spectrum becomes sharp, and high color purity can be achieved. However, in the light emitting device using the band edge emission, the off angle has not been studied so far.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light emitting device which utilizes band edge emission and has a high luminous efficiency.

[0005]

As a result of intensive studies in view of such a situation, the present inventors have found that a high quality semiconductor crystal can be obtained by setting the inclination angle of the substrate surface within a specific range. The inventors have found the present invention and have reached the present invention. That is, the present invention is the invention described below.

[1] On the sapphire substrate, the general formula In _x
Ga _y Al _z N (provided that, x + y + z = 1,0 ≦ x ≦
1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1), which is a light emitting device in which a compound semiconductor including at least two layers having different band gaps is laminated, and the sapphire has a substrate surface and a C surface. The angle formed by is less than 5 degrees, and band-edge light emission is performed. [2] A first group 3-5 compound semiconductor represented by the general formula Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) on a sapphire substrate, and Formula In _c Ga _d
A second 3-5 group compound semiconductor represented by N (where c + d = 1, 0 <c ≦ 1, 0 ≦ d <1) includes a structure formed in contact with each other in this order [ 1] described in 3-
Group 5 compound semiconductor light emitting device. [3] S contained in the layer of the second Group 3-5 compound semiconductor
The concentration of any of i, Ge and Group 2 elements is 1 × 10 ¹⁷
3-5 according to [2], which is less than or equal to cm ^-3
Group compound semiconductor light emitting device. [4] The 3-5 group compound semiconductor light-emitting device according to [2] or [3], wherein the thickness of the second 3-5 group compound semiconductor is 10 Å or more and 90 Å or less.

Next, the present invention will be described in detail. The group III-V compound semiconductor in the present invention, the general formula In _x Ga _y A
l _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y
A compound semiconductor having a structure in which at least two layers represented by ≦ 1, 0 ≦ z ≦ 1) are laminated. Since the compound semiconductor can have a band gap in the visible region depending on its composition, it is particularly important for display applications. Further, depending on the composition, a bandgap larger than that of a layer having a bandgap in the visible region can be formed. Therefore, with a layered structure of these layers, a layer with a large band gap can act as a charge injection layer with respect to a layer with a small band gap. In this case, the layer having a small band gap becomes the light emitting layer. In a semiconductor device having such a laminated structure, electrons and holes are confined in a light emitting layer having a small band gap, and the recombination probability there becomes extremely high. Therefore, high luminous efficiency can be achieved.

An example of the structure of a 3-5 group compound semiconductor in the light emitting device of the present invention is shown in FIGS. The first layer is a charge injection layer and has a larger band gap than the second layer. The second layer is a light emitting layer having a band gap in the visible region. In FIG. 1, a third layer having a bandgap larger than that of the second layer is grown on the second layer, and a fourth layer having a conductivity different from that of the first layer is further grown. Is. The electrodes are formed of the first layer and the fourth layer, and when a voltage is applied to the two electrodes, a current flows, and the second layer emits light. In FIG. 2, the third layer has conductivity different from that of the first layer. As in the example of FIG. 1, light is emitted by applying a voltage. The first layer is n-type because of the ease of crystal growth,
The fourth layer is generally p-type. In the example of FIG. 2 without the fourth layer, the third layer is p-type.

As the second layer which becomes the light emitting layer, In _c Ga
_d N (however, c + d = 1, 0 <c ≦ 1, 0 ≦ d <1)
Is preferred. The mixed crystal containing Al has a large band gap corresponding to the mixed crystal ratio of AlN. Therefore, in order to obtain a band gap capable of realizing blue light emission due to band edge emission, a mixed crystal of InN is required as compared with the case where Al is not contained. The crystal ratio must be increased. For that purpose, the decomposition temperature of InN is low, so that it is necessary to lower the growth temperature. However, since generally the crystal quality deteriorates when the growth temperature is lowered, In _x Ga _y N containing no Al is preferable. This In _c Ga _d N
Ga _a Al _b N (provided that a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) is preferable as the layer used as the underlayer. Since the mixed crystal containing In has a low decomposition temperature, it is usually 85.
The growth is performed at a temperature of 0 ° C. or lower. On the other hand, Ga _a
Since Al _b N has a high decomposition temperature and can be grown at a high temperature of about 1100 ° C., and the quality of the obtained crystal is good, Ga _a Al _b N is preferable as the underlayer.

The sapphire used as the substrate can be produced by a crystal pulling method such as the Czochralski method or the EFG method, and its surface can be mirror-polished. In the present invention, the angle formed between the substrate surface of the sapphire substrate and the C surface of the sapphire substrate is less than 5 degrees. More preferably, it is 4 degrees or less. If the angle formed with the C plane of the substrate surface is 5 degrees or more, a light emitting element using band edge emission using the compound semiconductor is not preferable because the luminous efficiency is not sufficient. The thickness of the substrate is preferably 0.1 mm or more and 1.0 mm or less. More preferably, it is 0.3 mm or more.
If the thickness of the substrate is less than 0.1 mm, after the compound semiconductor crystal is grown, the compound semiconductor crystal warps due to the difference in thermal expansion coefficient between the compound semiconductor and sapphire during cooling, which becomes a problem in the process of manufacturing an LED chip. Also, the thickness of the substrate is 1.0 mm
If the thickness is thicker, it becomes difficult to divide the substrate in manufacturing the LED chip, which is not preferable.

In order to realize a light emitting device using band edge emission, the amount of impurities contained in the second layer must be kept low. Specifically, the concentration of each element of Si, Ge and Group 2 elements is preferably 10 ¹⁷ cm ⁻³ or less. In case of band edge emission, the emission color is 3 of the second layer.
Determined by the composition of group elements. When emitting light in the visible region, In
The concentration is preferably 10% or more. When the In concentration is less than 10%, most of the emitted light is ultraviolet light, and sufficient brightness cannot be felt. The emission wavelength becomes longer as the In concentration increases, and the emission wavelength can be adjusted from purple to blue and green. The film thickness of the second layer is preferably 10 Å or more and 90 Å or less. When the film thickness is smaller than 10Å or larger than 90Å, the compound semiconductor is used as a light emitting device,
It is not preferable because the luminous efficiency is not sufficient.

As a method for producing a 3-5 group compound semiconductor in the present invention, metal organic vapor phase epitaxy (hereinafter referred to as MOVPE
It may be written. ) Method, molecular beam epitaxy (hereinafter,
Sometimes referred to as MBE. ) Method, hydride vapor phase epitaxy (hereinafter sometimes referred to as HVPE) method, and the like. When the MBE method is used, a gas source molecular beam epitaxy (hereinafter sometimes referred to as GSMBE) method that is a method of supplying nitrogen gas, ammonia, and other nitrogen compounds in a gaseous state as a nitrogen source. It is commonly used. In this case, the nitrogen raw material is chemically inactive, and the nitrogen atom may be difficult to be taken into the crystal. In that case, by exciting the nitrogen raw material by a microwave or the like to supply it in an activated state, it is possible to improve the nitrogen uptake efficiency.

In the case of MOVPE method, the following raw materials are used.
Can be used. That is, as the Group 3 raw material,
Chill gallium [(CH_Three)_ThreeGa, hereinafter referred to as "TMG"
Sometimes. ], Triethylgallium [(C_TwoH_Five)
_ThreeGa, hereinafter sometimes referred to as "TEG". ] General
Formula R₁R_TwoR_ThreeGa (where R₁, R _Two, R_ThreeIs a lower class
Represents a alkyl group. ) Trialkylgallium represented by
Trimethyl aluminum [(CH_Three)_ThreeAl], Trier
Chill aluminum [(C_TwoH_Five)_ThreeAl, hereinafter "TE
It may be written as "A". ], Triisobutylaluminium
Mu [(i-C_FourH₉)_ThreeGeneral formula R such as Al]₁R_TwoR_Three
Al (where R₁, R_Two, R_ThreeIs a lower alkyl group
You. ) Trialkylaluminum represented by;
Luamine Alan [(CH_Three)_ThreeN: AlH_Three]; Trime
Chill indium [(CH_Three)_ThreeIn, hereinafter referred to as "TMI"
There is a note. ], Triethylindium [(C_TwoH
_Five)_ThreeGeneral formula R such as In]₁R_TwoR_ThreeIn (here
R₁, R_Two, R_ThreeRepresents a lower alkyl group. )
Trialkylindium and the like. These are just
Used alone or as a mixture.

Next, examples of the Group 5 raw materials include ammonia, hydrazine, methylhydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, ethylenediamine and the like. These may be used alone or as a mixture. Among these raw materials, ammonia and hydrazine do not contain a carbon atom in the molecule, so that the contamination of the semiconductor with carbon is small and suitable.

[0015]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Example 1 A gallium nitride based semiconductor was produced by the MOVPE method. The angle between the substrate surface and the C plane is 0.0
Mirror-polished sapphire that was twice used was organically cleaned and used. First of all, as a buffer layer, T was grown at 600 ° C.
After forming 500 Å GaN film with MG and ammonia,
TMG, ammonia and silane (S
GaN doped with Si using iH ₄ ) at 1100 ° C.
Was deposited to a thickness of 3 μm. After cooling to 785 ° C,
Change the carrier gas from hydrogen to nitrogen, TEG, TMI,
In _0.3 Ga _0.7 N for 90 seconds using TEA
_0.8 Al _0.2 N was grown for 10 minutes. In _{0. 3} Ga _0.7 obtained from the relationship of the film thickness obtained and the growth time in the thick-
The growth rate of N was about 33Å / min, and the growth rate of Ga _0.8 Al _0.2 N was about 25Å / min. Therefore, the film thickness of these layers is about 50Å and about 250Å, respectively. Next, the temperature was raised to 1100 ° C., and TMG, ammonia, and Gp doped with Mg using Cp ₂ Mg as a dopant were used.
The aN has grown to 5000 Å. After the growth was completed, the substrate was taken out and heat-treated in nitrogen at 800 ° C. for 20 minutes.

The sample thus obtained was formed into an electrode by a conventional method to obtain an LED. Ni- as p-electrode
Au alloy was used, and Al was used as the n electrode. When a current of 20 mA was applied to this LED in the forward direction, a peak wavelength of 45
A clear blue light emission of 0 nm was exhibited, and the luminance was 265 mcd.

Comparative Example 1 An LED was prepared in the same manner as in Example 1 except that the angle between the substrate surface of the sapphire used and the C plane was 5 degrees.
The same evaluation as in Example 1 was performed. As a result, although it also emitted blue light, the luminance was 55 mcd.

Comparative Example 2 An LED was prepared in the same manner as in Example 1 except that the substrate surface of the sapphire used and the C-plane formed an angle of 10 degrees, and the same evaluation as in Example 1 was performed. . As a result, although it also emitted blue light, the luminance was 1 mcd or less.

[0019]

Industrial Applicability The light emitting device using band edge emission according to the present invention has high luminous efficiency and thus has great industrial value.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of a 3-5 group compound semiconductor used in a light emitting device of the present invention.

FIG. 2 is a cross-sectional view showing an example of the structure of a 3-5 group compound semiconductor used in the light emitting device of the present invention.

[Explanation of symbols]

 1. . . GaAlN (first layer) 1. . . InGaN (second layer) 3. . . InGaAlN (third layer) 4. . . GaAlN (fourth layer) 5. . . n electrode 6. . . p electrode

Claims (4)

[Claims] 1. A general formula of In _x Ga _y on a sapphire substrate.
Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦
y ≦ 1, 0 ≦ z ≦ 1), which is a light emitting device in which a compound semiconductor including at least two layers having different band gaps is laminated, and an angle formed between the substrate surface of the sapphire and the C surface is A 3-5 group compound semiconductor light-emitting device, which is less than 5 degrees and emits at a band edge. 2. A sapphire substrate having the general formula Ga _a Al _b.
A first 3-5 group compound semiconductor represented by N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) and the general formula In _c
Ga _d N (where c + d = 1, 0 <c ≦ 1, 0 ≦ d <
2. The 3-5 group compound semiconductor light-emitting device according to claim 1, wherein the second 3-5 group compound semiconductor represented by 1) includes a structure in which the second 3-5 group compound semiconductor is in contact in this order. 3. The concentration of any of Si, Ge and Group 2 elements contained in the layer of the second Group 3-5 compound semiconductor is 1 ×.
The 3-5 group compound semiconductor light emitting device according to claim 2, wherein the light emitting device has a size of 10 ¹⁷ cm ^-3 or less. 4. The thickness of the second group 3-5 compound semiconductor is 1
The 3-5 group compound semiconductor light emitting device according to claim 2 or 3, characterized in that it is 0 Å or more and 90 Å or less.