JP2004172649A - Method of improving brightness of group 3-5 compound semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving luminance of a group 3-5 compound semiconductor light emitting device which emits light by band edge emission.
[Solution]
(1) On a sapphire substrate, a first group 3-5 group represented by at least a general formula Ga _a Al _b N (a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) having _a different band gap. a compound semiconductor, the general formula in _c Ga _d N (provided that, c + d = 1,0 <c ≦ 1,0 ≦ d <1) and the second group III-V compound semiconductor represented by, in contact with this order In manufacturing a Group 3-5 compound semiconductor light emitting device having the following structure, a sapphire substrate is formed by using a substrate in which the angle between the substrate surface of the sapphire and the C plane is less than 5 degrees. A method for improving the brightness of a Group 3-5 compound semiconductor light emitting device, wherein the Group 3 compound semiconductor is a non-doped Group 3-5 compound semiconductor, and the thickness thereof is 10 ° or more and 90 ° or less.
[Selection diagram] None

Description

The present invention has 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) with a 3-5 group compound semiconductor represented by It relates to a light emitting element.

Ultraviolet or blue light-emitting diode (hereinafter, LED abbreviated) as a material for a light-emitting element such or ultraviolet or blue laser diode, 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) are known. In particular, those containing 10% or more of InN in a mixed crystal ratio are particularly important for display applications because the emission wavelength in the visible region can be adjusted according to the In concentration.
It has been attempted to form the Group 3-5 compound semiconductor on various substrates such as sapphire, GaAs and ZnO. In particular, sapphire is important because a large area and high quality single crystal can be relatively easily produced. For the plane orientation of the sapphire substrate, studies using A-plane, R-plane, C-plane and the like have been made, and among them, it is known that relatively good compound semiconductor can be obtained by using C-plane.
With respect to a light-emitting element using impurity emission of a gallium nitride-based compound semiconductor, the compound semiconductor is grown on a substrate (off-substrate) inclined several degrees from the C-plane of the sapphire substrate so as to have a non-mirror surface, thereby improving extraction efficiency. There is a report that the external quantum efficiency (luminous efficiency) can be improved by the improvement (Patent Document 1).
In general, a GaAs substrate having a low index plane orientation such as (001) or (111) is used for crystal growth of GaAs or the like. However, in practice, a slight angle (hereinafter abbreviated as an off angle) from these planes is used. A good crystal may be obtained by using a substrate having an inclined surface.

Here, the light emitting mechanism of the LED can be roughly classified into two. One is a mechanism in which injected electrons and holes are recombined via a level formed by impurities in a band gap, which is generally called impurity emission. In the other, the injected electrons and holes are recombined without passing through the level due to the impurity. 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 impurity light emission uses recombination of electrons and holes through impurity levels, a sufficient number of impurity levels are required to capture injected electrons or holes. When doped to a certain concentration, the crystal quality deteriorates. That is, the number of impurity levels that can be formed in a high-quality crystal is limited. In this case, if the injection amount of electrons and holes increases, the number of impurity levels becomes insufficient, and recombination of electrons and holes without passing through the impurity levels occurs. In other words, the luminous efficiency decreases at a high current. On the other hand, in the case of band-edge light emission, light emission that does not pass through impurity levels is used, and thus such a decrease in light emission efficiency does not occur. Therefore, when high current injection is required, band edge emission is preferred.
On the other hand, the compound semiconductor has a direct transition band gap, and the band gap can be set to a visible region depending on the composition. Therefore, by using this layer as a light emitting layer, a highly efficient light emitting element by band edge light emission can be manufactured without using impurity light emission. In the 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 element using this band edge emission, the off angle has not been studied so far.

JP-A-6-291368

  An object of the present invention is to provide a group III-V compound semiconductor light emitting device exhibiting high luminous efficiency using band edge light emission.

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

That is, the present invention
[1] On the sapphire substrate, the first group 3-5 group represented by at least the general formula Ga _a Al _b N (a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) having different band gaps a compound semiconductor, the general formula in _c Ga _d N (provided that, c + d = 1,0 <c ≦ 1,0 ≦ d <1) and the second group III-V compound semiconductor represented by, in contact with this order In manufacturing a Group 3-5 compound semiconductor light emitting device having the following structure, a sapphire substrate is formed by using a substrate in which the angle between the substrate surface of the sapphire and the C plane is less than 5 degrees. It is an object of the present invention to provide a method for improving the luminance of a group 3-5 compound semiconductor light emitting device, characterized in that the group 3 compound semiconductor is a non-doped group 3-5 compound semiconductor and the thickness thereof is not less than 10 ° and not more than 90 °.

Further, in the present invention, [2] the concentration of any of Si, Ge, and Group 2 elements in the layer in the second Group 3-5 compound semiconductor may be 1 × 10 ¹⁷ cm ⁻³ or less. Another object of the present invention is to provide a method for improving luminance of [1].

  Further, the present invention provides [3] the method for improving brightness according to [1] or [2], wherein the thickness of the second group III-V compound semiconductor is 10 ° or more and 50 ° or less.

  According to the method of the present invention, a group III-V compound semiconductor light-emitting device that emits light by band-edge emission and has improved luminance is industrially advantageous.

The group III-V compound semiconductor in the present invention, represented by general formula In _x Ga _y Al _z N (provided that, x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1) A compound semiconductor having a structure in which at least two layers are stacked.
The compound semiconductor is particularly important for display applications because the band gap can be set in the visible region depending on the composition. Depending on the composition, a band gap larger than a layer having a band gap in a visible region can be formed. Therefore, with a stacked structure of these layers, a layer having a large band gap can function as a charge injection layer for a layer having a small band gap. In this case, a layer having a small band gap becomes a light emitting layer. In a semiconductor element 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 is extremely high. Therefore, high luminous efficiency can be achieved.

FIGS. 1 and 2 show examples of the structure of the group 3-5 compound semiconductor in the light emitting device of the present invention. 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 a visible region. FIG. 1 shows that a third layer having a larger band gap than the second layer is grown on the second layer, and a fourth layer having a conductivity different from that of the first layer is grown. It is. The electrodes are formed on the first layer and the fourth layer. When a voltage is applied to the two electrodes, a current flows and light is emitted in the second layer.
FIG. 2 shows the third layer having conductivity different from that of the first layer. As in the example of FIG. 1, light is emitted by applying a voltage. In general, the first layer is of an n-type and the fourth layer is of a p-type for ease of crystal growth. In the example of FIG. 2 without the fourth layer, the third layer is p-type.

Emitting layer and formed of a second as the layers In _c Ga _d N (provided that, c + d = 1,0 <c ≦ 1,0 ≦ d <1) is preferable. In a mixed crystal containing Al, the band gap becomes large in accordance with the mixed crystal ratio of AlN. Therefore, in order to obtain a band gap capable of realizing blue light emission by band edge emission, compared to a case where Al is not contained, the band gap becomes large. The crystal ratio must be increased. Since the decomposition temperature of InN is low because its, although lowering the growth temperature is necessary, since the crystal quality generally lowering the growth temperature decreases, an In _c Ga _d N that does not contain Al are preferable.
This an In _c Ga _d As the layer used as the base of the N Ga _a Al _b N (provided that, a + b = 1,0 ≦ a ≦ 1,0 ≦ b ≦ 1) is preferred. Since the mixed crystal containing In has a low decomposition temperature, it is usually grown at a temperature of 850 ° C. or less. On the other hand, Ga _a Al _b N has _a high decomposition temperature and can be grown at a high temperature of about 1100 ° C., so that the quality of the obtained crystal is good. Therefore, Ga _a Al _b N is preferable as the underlayer.

Sapphire used as a substrate can be manufactured by a crystal pulling method such as a Czochralski method or an EFG method, and a mirror-polished surface thereof can be used.
In the present invention, the angle 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 between the substrate surface and the C-plane is 5 degrees or more, it is not preferable that the compound semiconductor is used as a light-emitting element using band-edge emission because the light-emitting efficiency is insufficient.
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, warpage occurs due to the difference in the coefficient of thermal expansion between the compound semiconductor and sapphire during cooling after growth of the compound semiconductor crystal, which is a problem in the process of manufacturing an LED chip. Further, if the thickness of the substrate is larger than 1.0 mm, it becomes difficult to divide the substrate in manufacturing the LED chip, which is not preferable.

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

As a method for producing a Group 3-5 compound semiconductor in the present invention, a metalorganic vapor phase epitaxy (hereinafter sometimes referred to as MOVPE) method, a molecular beam epitaxy (hereinafter abbreviated as MBE) method, hydride vapor phase epitaxy (Hereinafter abbreviated as HVPE).
When the MBE method is used, a gas source molecular beam epitaxy (hereinafter, sometimes referred to as GSMBE) method is a method of supplying nitrogen gas, ammonia, and other nitrogen compounds in a gaseous state as a nitrogen source. Commonly used. In this case, the nitrogen source may be chemically inert, and the nitrogen atoms may not be easily incorporated into the crystal. In that case, the nitrogen raw material is excited by a microwave or the like, and supplied in an activated state, whereby the nitrogen taking-in efficiency can be increased.

In the case of the MOVPE method, the following raw materials can be used.
That is, as a Group 3 raw material, general materials such as trimethylgallium ((CH ₃ ) ₃ Ga, hereinafter abbreviated as “TMG”) and triethylgallium [(C ₂ H ₅ ) ₃ Ga, abbreviated as “TEG”) and the like can be used. Trialkylgallium represented by the formula R ₁ R ₂ R ₃ Ga (where R ₁ , R ₂ and R ₃ represent lower alkyl groups); trimethylaluminum [(CH ₃ ) ₃ Al], triethylaluminum [( General formula R ₁ R ₂ R ₃ Al (here, R ₁ , R ₂ ) such as C ₂ H ₅ ) ₃ Al (hereinafter abbreviated as “TEA”), triisobutylaluminum [(i-C ₄ H ₉ ) ₃ Al]. ₂ , R ₃ represents a lower alkyl group); trimethylamine alane [(CH ₃ ) ₃ N: AlH ₃ ]; trimethyl indium [(CH ₃ ) ₃ In; hereinafter, abbreviated as “TMI”. Do), bird Trialkylindium represented by the general formula R ₁ R ₂ R ₃ In such as ethyl indium [(C ₂ H ₅ ) ₃ In] (where R ₁ , R ₂ , and R ₃ represent lower alkyl groups); Is mentioned.
These are used alone or as a mixture.

  Next, as Group 5 raw materials, ammonia, hydrazine, methylhydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, ethylenediamine, and the like can be given. These are 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.

  Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1
The gallium nitride based semiconductor was manufactured by the MOVPE method. As the substrate, sapphire whose substrate surface forms an angle of 0.02 degrees with the C-plane was mirror-polished and used after organic cleaning.
First, GaN was formed at 500 ° C. as a buffer layer at 600 ° C. using TMG and ammonia, and then GaN doped with Si at 1100 ° C. with a thickness of 3 μm using TMG, ammonia and silane (SiH ₄ ) as a dopant. Filmed.
After the temperature was decreased to 785 ° C., the carrier gas was changed from hydrogen to nitrogen, and In _0.3 Ga _0.7 N was grown for 90 seconds and Ga _0.8 Al _0.2 N was grown for 10 minutes using TEG, TMI, and TEA. The growth rate of In _0.3 Ga _0.7 N and the growth rate of Ga _0.8 Al _0.2 N obtained from the relationship between the growth time of the thick film and the obtained film thickness were about 33 ° / min and about 25 ° / min. Thus, the thicknesses of these layers are about 50 ° and about 250 °, respectively.
Next, the temperature was raised to 1100 ° C., and Mg-doped GaN was grown at 5000 ° using TMG, ammonia and Cp ₂ Mg as a dopant. After the growth was completed, the substrate was taken out and subjected to a heat treatment in nitrogen at 800 ° C. for 20 minutes.

  An electrode was formed on the sample thus obtained in accordance with a conventional method to obtain an LED. A Ni-Au alloy was used as the p electrode, and Al was used as the n electrode. When a current of 20 mA was passed through the LED in the forward direction, it emitted clear blue light with a peak wavelength of 450 nm, and the luminance was 265 mcd.

Comparative Example 1
An LED was manufactured in the same manner as in Example 1 except that the angle of the sapphire substrate surface to the C-plane was 5 degrees, and the same evaluation as in Example 1 was performed. As a result, the device still emitted blue light, but had a luminance of 55 mcd.

Comparative Example 2
An LED was fabricated in the same manner as in Example 1 except that the angle of the sapphire substrate surface to the C-plane was 10 degrees, and the same evaluation as in Example 1 was performed. As a result, the device also emitted blue light, but had a luminance of 1 mcd or less.

FIG. 5 is a cross-sectional view illustrating an example of the structure of a Group 3-5 compound semiconductor used for the light-emitting element of the present invention. FIG. 5 is a cross-sectional view illustrating an example of the structure of a Group 3-5 compound semiconductor used for the light-emitting element of the present invention.

Explanation of reference numerals

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

Claims (3)

A first group III-V compound semiconductor represented by at least general formula Ga _a Al _b N (a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) having different band gaps on a sapphire substrate; formula in _c Ga _d N (provided that, c + d = 1,0 <c ≦ 1,0 ≦ d <1) and the second group III-V compound semiconductor which is expressed by a structure in which contact with this order In manufacturing the group III-V compound semiconductor light-emitting device having the second group III-V compound semiconductor, a substrate having an angle between the substrate surface of the sapphire and the C-plane of less than 5 degrees is used as the sapphire substrate. Is a non-doped group III-V compound semiconductor, and the thickness thereof is not less than 10 ° and not more than 90 °. 2. The method according to claim 1, wherein the concentration of any one of Si, Ge, and Group 2 elements in the layer of the second Group 3-5 compound semiconductor is 1 × 10 ¹⁷ cm ⁻³ or less.   3. The method according to claim 1, wherein the thickness of the second group III-V compound semiconductor is 10 [deg.] To 50 [deg.].

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