JP2005191599A - Method for uniforming luminance in light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for uniforming luminance in the substrate surface of a light-emitting element using a group III-V compound semiconductor. <P>SOLUTION: In the method, vapor phase epitaxy is made to the first layer of the group III-V compound semiconductor expressed by a general expression In<SB>x</SB>Ga<SB>y</SB>Al<SB>z</SB>N (in this case, x+y+z=1, 0<x≤1, 0≤y<1, and 0≤z<1), and vapor phase epitaxy is made to a second layer expressed by a general expression In<SB>u</SB>Ga<SB>v</SB>Al<SB>w</SB>N (in this case, u+v+w=1, 0≤u≤1, 0≤v≤1, and 0≤w≤1), thus manufacturing the group III-V compound semiconductor. In the method for uniforming the luminance in the substrate surface of the light-emitting element, the group III-V compound semiconductor is used, where the group III-V compound semiconductor is manufactured by the method for manufacturing the group III-V compound semiconductor having a process for supplying at least one kind of carrier gas selected from an inert gas, and a group V material without supplying a group III material before the growth of the second layer after the first layer is grown. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for uniformizing luminance within a substrate surface of a light emitting device using a Group 3-5 compound semiconductor.

Conventionally, as a material for light emitting elements such as light emitting diodes in the ultraviolet, blue, and green regions (hereinafter, referred to as LEDs) or laser diodes in the ultraviolet, blue, and green regions, the general formula In _x Ga _y Al _z N ( However, a group 3-5 compound semiconductor represented by x + y + z = 1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1) is known.

Since the compound semiconductor cannot obtain good crystals in bulk growth, homoepitaxial growth using the compound semiconductor itself as a substrate is difficult.
By the way, the compound semiconductor represented by the general formula Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) has good crystallinity by using a buffer layer such as GaN or AlN. It is known that you can get things. Since the Ga _a Al _b N has the same group 5 element as the In _x Ga _y Al _z N and has the same crystal structure, the In _x Ga _y Al _z N is the same as the Ga _a High crystallinity can be obtained by growing on Al _b N.

  By the way, the lattice constant of the compound semiconductor greatly varies depending on the mixed crystal ratio. In particular, since the lattice constant of InN is about 12% or more larger than that of GaN or AlN, a large difference may occur in the lattice constant between layers depending on the mixed crystal ratio of each layer of the compound semiconductor. . When there is a large lattice mismatch, a defect may occur in the crystal, which causes a decrease in crystallinity. In general, it is difficult to realize high light emission efficiency in a light-emitting element manufactured using a crystal including many defects.

  In order to suppress the occurrence of defects due to lattice mismatch, the thickness of the layer must be reduced according to the magnitude of strain due to lattice mismatch. However, when the active layer is a very thin layer, the physical properties of the light-emitting layer are affected by the mixed crystal ratio of the light-emitting layer or slight fluctuations in the layer thickness, and the target emission wavelength is uniformly distributed over the entire substrate surface. Alternatively, it was difficult to manufacture a light-emitting element having emission intensity.

  An object of the present invention is to provide a method for uniformizing luminance within a substrate surface of a light emitting device using a Group 3-5 compound semiconductor.

  As a result of intensive studies on the growth conditions of the Group 3-5 compound semiconductor thin film, the present inventors have stopped the supply of the Group 3 raw material until the next layer is grown after the compound semiconductor thin film is grown. As a result, it was found that a high-quality and uniform thin film can be obtained, and the present invention has been achieved.

That is, the present invention is the invention described below.
[1] First group 3-5 compound semiconductor represented by the general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1) Is vapor-grown, and then the second layer is expressed by the general formula In _u Ga _v Al _w N (where u + v + w = 1, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1). In the method for producing a group 3-5 compound semiconductor by vapor phase growth of the first layer, after the first layer is grown, the group 3 raw material is not supplied and the inert gas is selected before the second layer is grown. In the substrate surface of a light emitting device, using a group 3-5 compound semiconductor produced by a method for producing a group 3-5 compound semiconductor comprising a step of supplying at least one kind of carrier gas and a group 5 raw material Brightness uniformity method.
[2] The method for uniformizing luminance according to [1], wherein the InN mixed crystal ratio of the first layer is 5% or more.

[3] The method for uniformizing luminance according to [1] or [2], wherein the thickness of the first layer is 10 to 500 mm.
[4] The concentration of each element of Si, Ge, Cd, Zn and Mg contained in the first layer is 10 ¹⁹ cm ⁻³ or less, [1], [2] or [ [3] The method for equalizing luminance according to [3].

  According to the present invention, when used as a light emitting device, a light emitting device having a uniform light emitting state and a high yield can be obtained, which is extremely useful and has great industrial value.

Next, the present invention will be described in detail.
Generally, sapphire, ZnO, GaAs, Si, SiC, NGO (NdGaO ₃ ), spinel (MgAl ₂ O ₄ ) or the like is used as a substrate for crystal growth of the Group 3-5 compound semiconductor. In particular, sapphire is preferable because it is transparent and high quality crystals with a large area can be obtained.

  Examples of the method for producing the Group 3-5 compound semiconductor include molecular beam epitaxy (hereinafter sometimes referred to as MBE) method, metal organic vapor phase epitaxy (hereinafter also referred to as MOVPE) method, and hydride vapor phase. A growth (hereinafter referred to as HVPE) method or the like is known. Among these, the MOVPE method is preferable because a uniform film can be formed over a large area, and the method for producing a Group 3-5 compound semiconductor in the present invention is based on the MOVPE method.

In the method for producing a Group 3-5 compound semiconductor in the present invention, the following raw materials can be used.
That is, the Group 3 raw material may be described as trimethylgallium [(CH ₃ ) ₃ Ga, hereinafter TMG. ], Triethylgallium [(C ₂ H ₅ ) ₃ Ga, hereinafter sometimes referred to as TEG. ], Etc. Trialkylgallium represented by the general 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 [(C ₂ H ₅ ) ₃ Al, hereinafter referred to as TEA. ], Triisobutylaluminum [(i-C ₄ H ₉ ) ₃ Al], and the like, represented by the general formula R ₁ R ₂ R ₃ Al (where R ₁ , R ₂ and R ₃ represent lower alkyl groups). Trialkylaluminum; trimethylamine allane [(CH ₃ ) ₃ N: AlH ₃ ]; trimethylindium [(CH ₃ ) ₃ In, hereinafter sometimes referred to as TMI. ], Triethylindium [(C ₂ H ₅ ) ₃ In] and other general formulas R ₁ R ₂ R ₃ In (where R ₁ , R ₂ and R ₃ represent lower alkyl groups) Examples include indium. These may be used alone or in combination.

Next, examples of the Group 5 raw material include ammonia, hydrazine, methyl hydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, and ethylenediamine. These may be used alone or in combination. Among these raw materials, ammonia and hydrazine are preferable because they do not contain carbon atoms in their molecules and thus cause less carbon contamination in the semiconductor.
Group 2 elements are important as the p-type dopant of the Group 3-5 compound semiconductor. Specific examples include Mg, Zn, Cd, Hg, and Be. Among these, Mg that is easy to produce a low-resistance p-type is preferable.
Mg dopant materials include biscyclopentadienylmagnesium, bismethylcyclopentadienylmagnesium, bisethylcyclopentadienylmagnesium, bis-n-propylcyclopentadienylmagnesium, bis-i-propylcyclopentadienylmagnesium It is preferable that the organometallic compound represented by the general formula (RC ₅ H ₄ ) ₂ Mg (wherein R represents H or a lower alkyl group having 1 to 4 carbon atoms) has an appropriate vapor pressure. It is.
As the n-type dopant of the Group 3-5 compound semiconductor, the Group 4 element and the Group 6 element are important. Specific examples include Si, Ge, and O. Among these, Si is preferable because it can easily produce a low-resistance n-type and can provide a material with high purity. As a raw material for the Si dopant, silane (SiH ₄ ), disilane (Si ₂ H ₆ ), and the like are suitable.
Examples of the carrier gas include inert gases such as nitrogen and argon. Nitrogen is preferable because a high-purity gas can be easily obtained.

In the present invention, after growing the first layer represented by the general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1). formula in _u Ga _v Al _w N (provided that, u + v + w = 1,0 ≦ u ≦ 1,0 ≦ v ≦ 1,0 ≦ w ≦ 1) a second layer before the vapor phase growth represented by It has the process of supplying a carrier gas or supplying a carrier gas and a Group 5 material without supplying a Group 3 material.
By having a step of interrupting growth without supplying the Group 3 raw material (hereinafter, sometimes referred to as a growth interrupting step), the reason is not clear, but a uniform Group 3-5 compound semiconductor is obtained. In particular, when the Group 3-5 compound semiconductor is used for a light-emitting element, a light-emitting element that emits light with a uniform wavelength and intensity within a substrate surface can be obtained. In particular, there is a remarkable effect for a layer containing 5% or more of InN by a mixed crystal ratio. It is considered that the crystal of the first layer is modified by having the growth interruption step.
When the growth interruption time is sufficiently short, the Group 5 raw material may or may not be supplied. However, if the growth interruption is long, the crystallinity of the first layer may deteriorate unless the Group 5 material is supplied, so it is preferable to supply the Group 5 material.
The time during which growth is interrupted depends on the temperature and atmosphere at which growth is interrupted, but if it is too short, the effect of the growth interruption is not sufficient, and if it is too long, it is difficult to obtain the desired InN mixed crystal ratio. A preferable growth interruption time is 1 second or more and 60 minutes or less, and more preferably 30 seconds or more and 30 minutes or less.

Hereinafter, the effect of the growth interruption process will be specifically described.
FIG. 1 shows an example of a quantum well structure that can be manufactured using the compound semiconductor. The buffer layer 2 is grown on the substrate 1, and further the Ga _a Al _b N layer 3, the In _x Ga _y Al _z N layer 4 which is the first layer of the present invention, and the second layer of the present invention. An In _u Ga _v Al _w N layer 5 is grown. By forming _a so-called double hetero structure in which the band gap of the Ga _a Al _b N layer 3 and the In _u Ga _v Al _w N layer 5 is larger than that of the In _x Ga _y Al _z N layer 4, In _x Ga _y Al _z N The layer 4 becomes a quantum well layer, and strong photoluminescence (hereinafter sometimes referred to as PL) from the quantum well layer is observed.
In this case, the emission wavelength of PL mainly depends on the composition of the group 3 element of the quantum well layer and the layer thickness of the quantum well layer. The PL intensity strongly reflects the crystallinity of the structure including the quantum well layer. Generally, the higher the crystallinity, the stronger the PL intensity. For this reason, by evaluating the semiconductor having the structure of FIG. 1 using PL, the mixed crystal ratio of the quantum well layer, the layer thickness, the crystallinity of the stacked structure including the quantum well, and the uniformity in the substrate plane Can be evaluated.
When the second layer is grown immediately after the growth of the first layer without interrupting the growth, the PL emission wavelength and intensity in the substrate surface are strongly non-uniform compared to when the growth is interrupted. The PL strength is weak overall. As the growth interruption time becomes longer, the uniformity of PL emission wavelength and intensity within the substrate surface is improved, and the PL intensity is also increased overall. However, as the growth interruption time becomes longer, the PL emission wavelength tends to be shorter. Therefore, when the growth interruption is performed for a long time, the mixed crystal ratio of the first layer is considered in consideration of the wavelength shift. It is preferable to adjust in advance.
In the above example, there is only one first layer. However, in the case of a structure in which a plurality of the compound semiconductors are laminated, a laminated layer having excellent uniformity by providing an appropriate growth interruption step after the growth of each layer. A structure can be made.

Next, a light-emitting element obtained using a Group 3-5 compound semiconductor obtained by the method for producing a Group 3-5 compound semiconductor in the present invention will be described.
In the quantum well structure shown in FIG. 1, the layers 3 and 5 in contact with the light emitting layer 4 have different conductivities, whereby a light emitting element having a double hetero structure is obtained. In view of ease of growth, the layer below the light emitting layer is generally n-type. After the growth of the light emitting layer, the growth is interrupted, whereby a semiconductor substrate of a light emitting element with excellent uniformity and high light emission efficiency can be manufactured.
In order to impart conductivity to the layers in contact with the active layer, these layers are doped with impurities. However, the doping may reduce the crystallinity of these layers, resulting in a decrease in luminous efficiency. . In such a case, the light emission efficiency may be improved by providing a low impurity concentration layer between the active layer and these layers. An example of such a structure is shown in FIG.

Although FIG. 2 shows an example in which a single quantum well layer is a light emitting layer, the layer functioning as the light emitting layer may be a layer composed of a plurality of layers. Specifically, an example in which a layer composed of a plurality of layers functions as a light emitting layer includes a structure in which two or more light emitting layers are stacked with a layer having a larger band gap.
When the first layer which is a light emitting layer contains Al, impurities such as O are easily taken in, and when used as the light emitting layer, the light emission efficiency may be lowered. In such a case, as the light emitting layer, a material expressed by the general formula In _x Ga _y N (where x + y = 1, 0 <x ≦ 1, 0 ≦ y <1) not including Al is used. Can do.

As already explained, since the lattice constant of the Group 3-5 compound semiconductor varies greatly depending on the mixed crystal ratio, there is a large lattice mismatch in the lattice constant between the layers of the Group 3-5 compound semiconductor. In some cases, the layer thickness must be reduced depending on the amount of strain due to lattice mismatch. The preferred thickness range depends on the magnitude of the strain. When the group 3-5 compound semiconductor having an InN mixed crystal ratio of 10% or more is stacked on the Ga _a Al _b N, the preferred thickness of the layer containing In is 5 to 500 mm. When the thickness of the layer containing In is less than 5 mm, the light emission efficiency is not sufficient. On the other hand, if it is larger than 500 mm, defects are generated and the luminous efficiency is not sufficient. A more preferable thickness range is 5 mm or more and 90 mm or less.
In addition, by reducing the thickness of the light emitting layer, charges can be confined in the light emitting layer with high density, so that the light emission efficiency can be improved. For this reason, even when the difference in lattice constant is smaller than that in the above example, the layer thickness of the light emitting layer is preferably the same as that in the above example.

By doping the light emitting layer with an impurity, light can be emitted at a wavelength different from the band gap of the light emitting layer. Since this is light emission from impurities, it is called impurity light emission. In the case of impurity emission, the emission wavelength is determined by the composition of the Group 3 element in the light emitting layer and the impurity element. In this case, the InN mixed crystal ratio of the light emitting layer is preferably 5% or more. When the InN mixed crystal ratio is less than 5%, the emitted light is almost ultraviolet rays, and a sufficient brightness cannot be felt. As the In mixed crystal ratio increases, the emission wavelength becomes longer, and the emission wavelength can be adjusted from purple to blue to green.
As an impurity suitable for impurity light emission, a group 2 element is preferable. Among group 2 elements, doping with Mg, Zn, and Cd is preferable because of high luminous efficiency. In particular, Zn is preferable. The concentration of these elements is preferably 10 ¹⁸ to 10 ²² cm ⁻³ .
The third layer may be simultaneously doped with Si or Ge together with these Group 2 elements. A preferable concentration range of Si and Ge is 10 ¹⁸ to 10 ²² cm ⁻³ .

In the case of impurity emission, the emission spectrum generally becomes broad, and the emission spectrum may shift as the amount of injected charge increases. For this reason, when high color purity is required or when it is necessary to concentrate light emission power in a narrow wavelength range, it is advantageous to use band edge light emission. In order to realize a light emitting element using band edge light emission, the amount of impurities contained in the light emitting layer must be kept low. Specifically, the concentration of each element of Si, Ge, Mg, Cd and Zn is preferably 10 ¹⁹ cm ⁻³ or less. More preferably, it is 10 ¹⁸ cm ⁻³ or less.

  In the case of band edge emission, the emission color is determined by the composition of the Group 3 element in the emission layer. When light is emitted in the visible part, the InN mixed crystal ratio is preferably 10% or more. When the InN mixed crystal ratio is smaller than 10%, the emitted light is almost ultraviolet light, and sufficient brightness cannot be felt. As the InN mixed crystal ratio increases, the emission wavelength becomes longer, and the emission wavelength can be adjusted from purple to blue to green.

When the mixed crystal ratio of InN in the light emitting layer is high, thermal stability is not sufficient, and deterioration may occur during crystal growth or in a semiconductor process. For the purpose of preventing such deterioration of the light emitting layer, the second layer of the present invention grown next to the light emitting layer can be provided with a protective function. In order to provide a sufficient protective function to the second layer, the InN mixed crystal ratio of the second layer is preferably 10% or less, and the AlN mixed crystal ratio is preferably 5% or more. More preferably, the InN mixed crystal ratio is 5% or less, and the AlN mixed crystal ratio is 10% or more.
In order to provide the second layer with a sufficient protective function, the thickness of the second layer is preferably 10 to 1 μm. More preferably, it is 50 to 5000 inches. If the thickness of the protective layer is less than 10 mm, sufficient effects cannot be obtained. On the other hand, when it is larger than 1 μm, the luminous efficiency is decreased, which is not preferable.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these.
Example 1
A Group 3-5 compound semiconductor having the structure shown in FIG. 1 was prepared by the MOVPE method, the PL spectrum was measured, and the in-plane distribution of the emission state was evaluated.
A substrate obtained by mirror polishing a 25 mm × 25 mm sapphire C surface was used. The growth was performed by a two-step growth method using GaN as a low temperature growth buffer layer. A GaN layer 3 having a thickness of about 2.5 μm was grown at normal pressure. Next, the reactor pressure is 0.5 atm, the substrate temperature is 785 ° C., the carrier gas is nitrogen, and carrier gas, TEG, TMI, and ammonia are supplied at 6 slm, 0.04 sccm, 0.4 sccm, and 4 slm, respectively. The In _0.3 Ga _0.7 N layer 4 as the first layer was grown for 70 seconds. However, slm and sccm are units of gas flow rate. 1 slm indicates that a gas having a weight that occupies a volume of 1 liter in a standard state flows per minute, and 1000 sccm corresponds to 1 slm.

After maintaining the state of supplying only nitrogen and ammonia as a growth interruption step for 5 minutes, TEG, TEA and ammonia were further supplied at the same temperature at 0.032 sccm, 0.008 sccm and 4 slm, respectively. A Ga _0.8 Al _0.2 N layer 5 as a layer was grown for 10 minutes.
It should be noted that the layer thicknesses of the layer 4 and the layer 5 are obtained from the above growth time because the growth rates obtained from the thicknesses of the layers grown for a longer time under the same conditions are 43 Å / min and 30 Å / min, respectively. The resulting layer thickness can be calculated as 50 mm and 300 mm, respectively.
When the group 3-5 compound semiconductor sample prepared as described above was subjected to PL measurement at room temperature using 325 nm emission of a He—Cd laser as an excitation light source, the peak wavelength was observed on the entire surface within the substrate surface except for the peripheral 5 mm. Strong light emission around 5000 mm was observed.
FIG. 3 shows a typical PL spectrum. The detector output at the peak wavelength of the spectrum was 7.4 mV.

Example 2
A sample was prepared in the same manner as in Example 1 except that the growth interruption time was 2 minutes. When the PL measurement at room temperature of this sample was carried out in the same manner as in Example 1, a portion with weak PL was partially observed in the substrate surface excluding the periphery of 5 mm. Similarly, strong PL was shown. A typical PL spectrum of the strong and weak parts of PL is shown in FIG.
The area ratio of the strong PL portion and the weak PL portion in the substrate surface was approximately 3: 1. The peak intensities of the spectra from the strong PL portion and the weak PL portion were approximately 4 mV and 0.17 mV, respectively.

Comparative Example 1
A sample was prepared in the same manner as in Example 1 except that after the first layer 4 was grown, the Ga _0.8 Al _0.2 N layer 5 was grown without interrupting the growth. When this sample was evaluated for PL at room temperature in the same manner as in Example 1, although there was a portion emitting light, no light emission was observed over almost the entire surface. FIG. 5 shows the PL spectrum of the portion that emits the strongest light. The peak intensity was only about 0.1 mV.

Example 3
A GaN buffer layer 2 is formed in the same manner as in Example 1, and TMG, ammonia and silane gas are supplied at 1100 ° C. to grow a Si-doped n-type GaN layer 6 having a thickness of 2.5 μm. TMG and ammonia are supplied at a temperature to grow a non-doped GaN layer 7 by 1500 mm. Next, the substrate temperature is lowered to 785 ° C., TEG, TMI and ammonia are supplied using nitrogen as a carrier gas to grow 50 μm of In _0.3 Ga _0.7 N layer 4. After maintaining the state in which only nitrogen and ammonia are supplied for 5 minutes, TEG, TEA and ammonia are further supplied at the same temperature to grow a Ga _0.8 Al _0.2 N layer 5 by 300 mm.
Next, the substrate temperature is raised to 1100 ° C., and TMG, Cp 2 Mg, and ammonia are supplied to grow GaN layer 8 doped with Mg by 5000 mm.
After the 3-5 group compound semiconductor sample produced as described above is taken out of the reaction furnace, it is annealed in nitrogen to make the GaN layer doped with Mg into a low resistance p-type layer. By forming an electrode on the sample obtained in this manner by a conventional method to obtain an LED, the LED can be fabricated with good uniformity within the substrate surface.

FIG. 3 shows a structure of a Group 3-5 compound semiconductor according to Example 1. FIG. 6 shows a structure of a compound semiconductor light-emitting element according to Example 3. The figure which shows PL spectrum in Example 1. FIG. The figure which shows PL spectrum in Example 2. FIG. The figure which shows PL spectrum in the comparative example 1.

Explanation of symbols

1 ... substrate 2 ... buffer layer 3 ... Ga _a Al _b N layer _{4 ... In x Ga y Al z} N layer _{5 ... In u Ga v Al w} N layer 6 ... n-type GaN layer 7 ... undoped GaN layer 8 ... p-type GaN layer

Claims (6)

A first layer of a Group 3-5 compound semiconductor represented by the general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1) Vapor phase growth and then a second layer represented by the general formula In _u Ga _v Al _w N (where u + v + w = 1, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1) In the method for producing a Group 3-5 compound semiconductor by vapor phase growth, after the first layer is grown, at least one selected from an inert gas without supplying a Group 3 raw material before the growth of the second layer. Use of a Group 3-5 compound semiconductor produced by a method of producing a Group 3-5 compound semiconductor having a step of supplying a seed carrier gas and a Group 5 raw material, and a luminance in-plane of the substrate of the light emitting device Uniformity method.   2. The method for uniformizing luminance according to claim 1, wherein the inert gas is nitrogen.   The method for equalizing luminance according to claim 1 or 2, wherein the Group 5 raw material is ammonia.   The method for equalizing luminance according to any one of claims 1 to 3, wherein an InN mixed crystal ratio of the first layer is 5% or more.   The method of claim 1, wherein the first layer has a thickness of 5 to 500 mm. The brightness of any one of claims 1 to 5, wherein the concentration of each element of Si, Ge, Cd, Zn, and Mg contained in the first layer is 10 ¹⁹ cm ^-3 or less. Uniformity method.

Images