JP2007294985A - Light emitting device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device using a nitride semiconductor for realizing a high power light emission with a high efficient light emission, and to provide a method of manufacturing the same. <P>SOLUTION: A GaN substrate 1 is formed, and a first conductive type Alx1Ga1-x1N layer (0≤x1≤1) is formed on the first main plane of the GaN substrate 1. A light emitting layer containing an InAlGaN quaternary mixed crystal is formed on the first conductive type Alx1Ga1-x1N layer. A second conductive type Alx2Ga1-x2N layer (0≤x2≤1) is formed on the light emitting layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting device and a method for manufacturing the same, and more specifically to a light emitting device using a nitride semiconductor that emits ultraviolet light and a method for manufacturing the same.

Since GaN-based compound semiconductors have a large band gap, they function as blue LEDs (Light Emitting Diodes) and ultraviolet LEDs, and are often used as excitation light sources for white LEDs. In order to improve the performance of these GaN-based LEDs that emit ultraviolet light having a short wavelength, for example, the following proposals have been made.
(D1) Using an SiC substrate, using an InAlGaN layer as a light emitting layer, and adjusting the composition ratio of In or the like in the InAlGaN layer, light emission in the ultraviolet region with a wavelength of 360 nm or less is made highly efficient (Patent Document 1).
(D2) High luminance is achieved by using a single-layer quantum well structure composed of Al _0.1 Ga _0.9 N layer / Al _0.4 Ga _0.6 N layer formed on a GaN substrate as a light emitting layer (Non-patent Document 1).
JP 2001-237455 A T.Nishida, H.Saito, N.Kobayashi; Appl.Phys. Lett., Vol.79 (2001) 711

  However, the above-described ultraviolet light emitting element has a problem in that the light emission efficiency is low and the light emission efficiency is lowered due to heat generation when a large current is passed for use in illumination or the like. The reason why the light emitting efficiency of the ultraviolet light emitting element is low is that the dislocation density in the substrate, the light emitting layer, etc. is high, so that these dislocations work as non-light emitting centers. In particular, when a sapphire substrate is used, the heat dissipation is poor, and the luminous efficiency tends to saturate in the middle without increasing linearly in proportion to the input.

  An object of the present invention is to provide a light-emitting element capable of realizing high-efficiency light emission and high-output light emission, and a method for manufacturing the same.

  The light emitting device of the present invention includes a light emitting layer containing an InAlGaN quaternary mixed crystal on the first main surface side of the nitride semiconductor substrate.

According to the above configuration, by using the nitride semiconductor substrate having a low dislocation density, it is possible to suppress the threading dislocation density that operates as a non-luminescent center in the light emitting element, and to increase the light emission efficiency. Further, the luminous efficiency can be further increased by the composition modulation effect by In contained in the InAlGaN quaternary mixed crystal. The nitride semiconductor substrate has conductivity of the first conductivity type, and is included in the GaN substrate, the Al _x Ga _1-x N substrate (0 <x ≦ 1), and the Al _x Ga _1-x N substrate. Any nitride semiconductor such as an AlN substrate may be used.

Another light emitting device of the present invention includes a first conductivity type Al _x1 Ga _1-x1 N layer (0 ≦ x1 ≦ 1) and a first conductivity type Al _x1 Ga _1-x1 N layer. Between the two conductivity type Al _x2 Ga _1-x2 N layer (0 ≦ x2 ≦ 1) and the first conductivity type Al _x1 Ga _1-x1 N layer and the second conductivity type Al _x2 Ga _1-x2 N layer And a light emitting layer containing an InAlGaN quaternary mixed crystal, and a nitride semiconductor layer having a thickness of 100 μm or less and far from the first conductivity type Al _x1 Ga _1-x1 N layer as viewed from the light emitting layer Prepare.

  The nitride semiconductor layer having a thickness of 100 μm or less is obtained by etching or peeling the nitride semiconductor substrate in the present invention. With this configuration, the threading dislocation density that operates as a non-luminescent center can be suppressed, and the composition modulation effect by In contained in the InAlGaN quaternary mixed crystal can be obtained, and absorption by the nitride semiconductor substrate can be prevented.

The method for manufacturing a light emitting device according to the present invention includes a step of forming a first conductivity type Al _x1 Ga _1-x1 N layer (0 ≦ x1 ≦ 1) on the first main surface side of a nitride semiconductor substrate; Forming a light emitting layer containing an InAlGaN quaternary mixed crystal on the first conductivity type Al _x1 Ga _1-x1 N layer; and a second conductivity type Al _x2 Ga _1-x2 N layer on the light emission layer ( 0 ≦ x2 ≦ 1) and a step of removing the nitride semiconductor substrate after forming the second conductivity type Al _x2 Ga _1-x2 N layer.

  For example, since GaN absorbs ultraviolet light having a wavelength of 360 nm or less, the light output can be improved by removing or peeling the GaN substrate according to the above method. As a result, the light output can be further improved. Also, other nitride semiconductors may absorb light in a wavelength range desired to be extracted. In such a case, the light output can be improved by removing the nitride semiconductor substrate.

  The B layer being positioned on the A layer means that the B layer is positioned farther from the A layer as viewed from the nitride semiconductor substrate, and the B layer may be in contact with the A layer. , You do not have to touch.

Next, examples of the present invention will be described.
Example 1
FIG. 1 is a diagram showing an LED according to Example 1 of the present invention. In FIG. 1, on a GaN substrate 1, (n-type GaN layer 2 / n-type Al _x Ga _1-x N layer 3 / InAlGaN light emitting layer 4 / p-type Al _x Ga _1-x N layer 5 / p-type GaN A layered structure of layer 6) is formed. An n-electrode 11 is disposed on the back surface, which is the second main plane of the GaN substrate 1, and a p-electrode 12 is disposed on the p-type GaN layer 6. By applying a current to the pair of n electrode 11 and p electrode 12, ultraviolet light is emitted from the InAlGaN light emitting layer. InAlGaN emitting layer has a composition of _{In xa Al ya Ga 1-xa} -ya N.

The GaN LED shown in FIG. 1 is manufactured by the following processing steps. A GaN substrate having a thickness of 400 μm, a dislocation density of 5E6 cm ⁻² , and a specific resistance of 1E-2 Ωcm is placed on a susceptor in a MOCVD (Metal Organic Chemical Vapor Deposition) film forming apparatus, and the pressure in the film forming apparatus is reduced. Then, a laminated structure was formed by the following MOCVD method to produce an ultraviolet light emitting diode.

As raw materials for MOCVD, trimethylgallium, trimethylaluminum, trimethylindium adduct, ammonia, tetraethylsilane, and bisethylcyclopentadinylmagnesium were used. First, an n-type GaN layer 2 having a thickness of 0.1 μm is formed on the GaN substrate 1 as a base layer at a growth temperature of 1050 ° C., and then an n-type Al _0.18 Ga _0.82 N layer having a thickness of 0.2 μm is formed thereon. 3 was deposited.

Thereafter, the growth temperature was lowered to 830 ° C., and a 60 nm InAlGaN light emitting layer 4 was grown. The flow rate of the raw material gas at this time was 2 l / min for ammonia, 3 μmol / min trimethylgallium, 0.5 μmol / min trimethylaluminum, and 60 μmol / min trimethylindium adduct. Thereafter, the growth temperature was raised again to 1050 ° C., and a p-type Al _0.18 Ga _0.82 N layer 5 having a thickness of 0.2 μm was formed. Further, a p-type GaN layer having a thickness of 30 nm was grown thereon as a contact layer.

  The LED epitaxial structure grown in this manner is made of an appropriate metal material, a translucent p-electrode 12 on the p-type GaN layer 6, and n on the surface opposite to the epitaxial layer (back surface) of the second surface of the GaN substrate. An electrode 11 was formed. The ultraviolet light emitting diode thus fabricated has the structure shown in FIG.

  When continuous current was applied to the ultraviolet light emitting diode, band edge emission of an InAlGaN light emitting layer having a wavelength of 360 nm was obtained as shown in FIG. Even when the applied current value was increased to 300 mA, the light output increased linearly without saturation as shown in FIG. This demonstrated high heat dissipation on the GaN substrate. Further, in this example, since a substrate having a low dislocation density was used as the GaN substrate, the threading dislocation density was reduced, and the luminous efficiency could be increased.

(Example 2)
FIG. 4 is a diagram showing an ultraviolet light-emitting diode according to Example 2 of the present invention. This ultraviolet light emitting diode has a buffer layer In _x Al _y Ga _{1 -xy} N layer 17 disposed on the side close to the GaN substrate 1 in contact with the light emitting layer 4 as compared with the laminated structure of the ultraviolet LED shown in FIG. There is a feature. The light emitting layer also has a multiple quantum well structure. The light emitting layer will be described later.

The manufacturing method of the ultraviolet LED of this example is as follows. As the GaN substrate 1, a substrate having a thickness of 400 μm and a threading dislocation density of 5E6 / cm ² was used. An n-type GaN layer 2 and an n-type Al _x Ga _1-x N layer 3 were formed in this order on the GaN substrate 1 by the same method as in Example 1. Next, an In _x Al _y Ga _1-xy N buffer layer 17 having a thickness of 50 nm is grown at a growth temperature of 830 ° C. in contact with the n-type Al _x Ga _1-x N layer 3.

Then, on top of the _{In x Al y Ga 1-xy} N buffer layer 17, as shown in FIG. _{5 (In x5 Al y5 Ga 1} -x5-y5 N barrier layer _{4a / In x4 Al y4 Ga 1} -x4- A multi-quantum well structure was formed by laminating two layers of _y4 N well layer 4b) in three cycles. In Example 2, the multiple quantum well structure constitutes the light emitting layer 4.

_{In x Al y Ga 1-xy} N when growing the buffer layer, and the _{In x4 Al y4 Ga 1-x4} -y4 flow rate of the source gas when growing the N barrier layer, ammonia 2l / min, trimethyl gallium 1 0.5 μmol / min, trimethylaluminum 0.65 μmol / min, and trimethylindium adduct 30 μmol / min.

The flow rate of the source gas when growing the In _x4 Al _y4 Ga _1-x4-y4 N well layer is as follows: ammonia is 2 l / min, trimethylgallium 1.5 μmol / min, trimethylaluminum 0.52 μmol / min, trimethylindium adduct 53 μmol / Min.

The present embodiment is different from the first embodiment in that the buffer layer In _x Al _y Ga _1-xy N layer is disposed and the light emitting layer has a multiple quantum well structure of an InAlGaN layer. .

  As a result of the above two improvements, the light emission output has been dramatically improved as shown in FIG. For example, in FIG. 3, the optical output with respect to the applied current of 100 mA was about 0.01 mW, but in FIG. 6, the optical output with respect to the applied current of 100 mA was 1.7 mW, which is a significant improvement of 150 times. Moreover, as shown in FIG. 7, the half width of the emission spectrum was as small as 12 nm. This is because light emission between the quantum levels becomes dominant because the light emitting layer is a multiple quantum well.

(Example 3)
In Example 3 of the present invention, an ultraviolet LED formed on a GaN substrate (example of the present invention) and a GaN template (a substrate obtained by growing 3 μm of n-type GaN on a sapphire substrate through a low-temperature grown GaN buffer layer). The light output was compared with the ultraviolet LED (comparative example). A GaN template prepared in advance was used. The laminated structure shown in FIG. 4 and FIG. 5 was formed in both the above inventive examples and comparative examples. However, since the back side of the GaN template is an insulator, the n-electrode was formed on the n-type GaN layer exposed in advance.

First, in manufacturing, both the GaN substrate and the GaN template were placed on the susceptor in the MOCVD film forming apparatus. Then, a GaN substrate, n-type GaN layer on the GaN template was formed _{In x Al y Ga 1-xy} N layer of n-type Al _x1 Ga _1-x1 N layer and a buffer layer. Thereafter, as in Example 2, a two-layer structure of (In _x4 Al _y4 Ga _1-x4-y4 N barrier layer / In _x3 Al _y3 Ga _1-x3-y3 N well layer) was laminated in three cycles, A multiple quantum well structure was fabricated. Thereafter, a p-type Al _x2 Ga _1-x2 N layer / p-type GaN layer was formed, and a p-electrode and an n-electrode were formed. Through the film formation process described above, the growth temperature and the flow rate of the source gas were made the same as in Example 2. However, the n-electrode to the GaN template is formed on the n-type GaN layer as described above.

  A current was applied to both the inventive example and the comparative example produced as described above, and the light output was measured. The results are shown in FIG. In FIG. 8, the comparative example using the GaN template displays a value five times the actual light output.

  According to FIG. 8, about 10 times the output on the GaN template is obtained with the LED on the GaN substrate at a current of 50 mA. In the LED using the GaN template, the output tends to be saturated at a current of 100 mA, whereas the output increased linearly on the GaN substrate. Therefore, the low dislocation GaN substrate is effective for increasing the efficiency of the ultraviolet LED using the InAlGaN light emitting layer and increasing the output of the LED by high current injection. In the LED of the present invention, a GaN substrate with good thermal conductivity is used, so that the high temperature due to heat generation is suppressed, and the non-luminescent center is suppressed because the threading dislocation density is low. The above high output was obtained.

Example 4
FIG. 9 is a view showing a laminated structure of light emitting elements in Example 4 of the present invention. First, the manufacturing method will be described. An Al _x Ga _1-x N substrate (x = 0.18) is placed on the susceptor, and a laminated structure is produced while keeping the inside of the metal organic vapor phase deposition apparatus under reduced pressure, thereby obtaining an ultraviolet light emitting diode structure. It was. As raw materials, trimethylgallium, trimethylaluminum, trimethylindium adduct, ammonia, tetraethylsilane, and bisethylcyclopentadienylmagnesium were used. First, an n-type Al _0.18 Ga _0.82 N buffer layer 22 having a thickness of 0.5 μm was grown at a growth temperature of 1050 ° C.

Thereafter, the growth temperature was lowered to 830 ° C., and the light emitting layer 24 having a multiple quantum well structure having three cycles of the InAlGaN barrier layer 24a and the InAlGaN well layer 24b was formed in the same manner as in Example 2 described above. Thereafter, the growth temperature was raised again to 1050 ° C., and a p-type Al _0.30 Ga _0.70 N layer 25 having a thickness of 20 nm and a p-type Al _0.18 Ga _0.82 N layer 26 having a thickness of 50 nm were grown.

  On the p-type AlGaN layer 26 having the LED epitaxial structure formed as described above, a semitransparent p-electrode 12 was formed from a metal material, and an n-electrode 11 was formed on the back side of the AlGaN substrate 21.

  When a continuous current was applied to the ultraviolet light emitting diode formed as described above, InAlGaN band edge emission with a wavelength of 351 nm could be obtained. As the optical output of the band edge emission, 8 mW was obtained when the current was 100 mA.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention including the above embodiments will be described enumerated.

  The nitride semiconductor substrate can be a GaN substrate. GaN substrates are suitable for mass production because they are large and inexpensive.

The nitride semiconductor substrate may be an Al _x Ga _1-x N substrate (0 <x ≦ 1). The crystallinity of the InAlGaN light emitting layer can be enhanced by using an Al _x Ga _1-x N substrate. That is, the difference in crystal lattice between the light emitting layer and the nitride semiconductor substrate can be reduced, and the lattice irregularity generated in the light emitting layer can be suppressed.

The band gap energy of the Al _x Ga _1-x N substrate (0 <x ≦ 1) can be set to be equal to or lower than the energy corresponding to the wavelength of light emitted from the light emitting layer containing the InAlGaN quaternary mixed crystal. By setting the band gap of such a nitride semiconductor substrate, light emitted from the light emitting layer is not absorbed by the nitride semiconductor substrate and can be used effectively.

A first conductivity type Al _x1 Ga _1-x1 N layer (0 ≦ x1 ≦ 1) and a first conductivity type as viewed from the nitride semiconductor substrate are formed on the first main surface side of the nitride semiconductor substrate. A second conductivity type Al _x2 Ga _1-x2 N layer (0 ≦ x2 ≦ 1) located farther than the Al _x1 Ga _1-x1 N layer, and the first conductivity type Al _x1 Ga _1-x1 N layer The above-described InAlGaN quaternary mixed crystal may be included between the second conductivity type Al _x2 Ga ₁ -x2 N layer.

  With the above configuration, high-efficiency light emission can be obtained by injecting current from the p-conductivity type layer and the n-conductivity type layer into the InAlGaN quaternary mixed crystal sandwiched therebetween.

  The light emitting element can emit light having a wavelength in the range of 330 nm to 370 nm by light emission in the light emitting layer.

  By adjusting the light emitting layer so that a wavelength in the above range is emitted, a light emitting element in the ultraviolet region with excellent light emission efficiency can be obtained.

The threading dislocation density of the nitride semiconductor substrate is preferably 1E7 cm ⁻² or less.
With this configuration, the threading dislocation density in the light emitting element of the present invention can be reduced, and the non-light emitting center density can be reduced.

Further, the same type of nitride semiconductor layer as that of the first conductive type nitride semiconductor substrate may be provided between the nitride semiconductor substrate and the first conductive type Al _x1 Ga _1-x1 N layer. .

According to this configuration, the same type of nitride semiconductor as that of the first conductivity type nitride semiconductor substrate is formed, rather than the structure in which the first conductivity type Al _x1 Ga _1-x1 N layer is formed in contact with the nitride semiconductor substrate. By making the layer function as a buffer layer, the crystallinity of the first conductivity type Al _x1 Ga _{1 -x1} N layer can be enhanced.

On the second conductivity type Al _x2 Ga _1-x2 N layer of the above, with Al _x3 Ga _1-x3 N layer of the second conductivity type having a thickness 1nm~500nm a (0 ≦ x3 <1, x3 <x2) It may be configured.

According to said structure, contact resistance can be made lower than forming an electrode in contact with the 2nd conductivity type _{Alx2Ga1 -x2N} layer, and power-light conversion efficiency can be improved. When the thickness of the second conductivity type Al _x3 Ga _1-x3 N layer is less than 1 nm, it is difficult to obtain a layer that can reduce the contact resistance. When the thickness exceeds 500 nm, absorption of ultraviolet light having a wavelength of 360 nm or less is not possible. The amount increases. For this reason, the thickness of the second conductivity type Al _x3 Ga _1-x3 N layer is in the range of ₁ nm to 500 nm.

The first electrode is paired with the first electrode on the second main surface opposite to the first main surface and on the second conductivity type Al _x2 Ga _1-x2 N layer. A configuration in which two electrodes are formed can be employed.

  According to said structure, since a 1st electrode can be arrange | positioned at the back surface which is the 2nd main surface of a nitride semiconductor substrate, series resistance can be made small. For this reason, voltage efficiency can be improved and heat generation can be reduced, so that luminous efficiency can be increased. Further, since nitride semiconductors have good thermal conductivity, they are less likely to be affected by heat generation.

The light-emitting layer includes a well layer represented by In _x4 Al _y4 Ga _1-x4-y4 N (0 <x4 <0.2, 0 <y4 <0.5), In _x5 Al _y5 Ga _{1-x5 A} structure having a quantum well structure including a barrier layer represented by _−y5 N (0 ≦ x5 <0.2, 0 <y5 <0.5) may be employed.

  As described above, the light emission efficiency can be greatly improved by making the light emitting layer have a quantum well structure. By using InAlGaN crystals for both the well layer and the barrier layer, the strain can be reduced and the light emission efficiency can be increased.

Between the light-emitting layer and the nitride semiconductor substrate, a structure having a _{In x Al y Ga 1-xy} N (0 <x <0.2,0 <y <0.5) layer having a thickness of 10nm~200nm It may be taken.

  With the above structure, distortion applied to the light-emitting layer can be reduced, spatial separation of electrons and holes due to the piezoelectric effect can be prevented, and light emission efficiency can be improved.

Total thickness of the first conductivity type Al _x1 Ga _1-x1 N layer (0 ≦ x1 ≦ 1) and the second conductivity type Al _x2 Ga _1-x2 N layer (0 ≦ x2 ≦ 1) May be 0.4 μm or less.

When the total thickness of the first conductivity type Al _x1 Ga _1-x1 N layer and the second conductivity type Al _x2 Ga _1-x2 N layer exceeds 0.4 μm, a crack is generated and corresponds to a part of these layers. Since the light is emitted only at the portion, the total thickness is preferably 0.4 μm or less.

In another light emitting device of the present invention, the nitride semiconductor substrate is etched or peeled off so that the nitride semiconductor layer does not have a distance from the first conductivity type Al _x1 Ga _{1 -x1} N layer when viewed from the light emitting layer. It may be.

  With this configuration, absorption in the short wavelength region by the nitride semiconductor substrate (nitride semiconductor layer) can be eliminated.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

By using the light emitting device of the present invention and the method for manufacturing the same, high output light emission can be realized by high efficiency light emission. Therefore, the light emitting device is expected to be widely applied to lighting applications as a light source for exciting white light emitting devices. Is done.

It is a figure which shows ultraviolet LED in Example 1 of this invention. It is a figure which shows the emission spectrum of ultraviolet LED of FIG. It is a figure which shows the relationship between the applied current and optical output of ultraviolet LED of FIG. It is a figure which shows ultraviolet LED in Example 2 of this invention. It is an enlarged view of the light emitting layer of FIG. It is a figure which shows the relationship between the applied current and optical output of ultraviolet LED of FIG. It is a figure which shows the emission spectrum of ultraviolet LED of FIG. It is a figure which shows the relationship between the applied current and light output of ultraviolet LED of the example of this invention in Example 3 of this invention, and ultraviolet LED of a comparative example. It is a figure which shows the laminated structure of ultraviolet LED in Example 4 of this invention.

Explanation of symbols

1 GaN substrate, 2 n-type GaN layer, 3 n-type Al _x1 Ga _1-x1 N layer, 4 InAlGaN light emitting layer, 4a In _x5 Al _y5 Ga _1-x5-y5 N layer (barrier layer), 4b In _x4 Al _y4 Ga _1-x4-y4 n layer (well layer), 5 p-type Al _x2 Ga _1-x2 n layer, 6 p-type GaN layer, 11 n electrode, 12 p _{electrode, 17 In x Al y Ga 1} -xy n buffer Layer, 21 n-type Al _0.18 Ga _0.82 N substrate, 22 n-type Al _0.18 Ga _0.82 N layer, 24a InAlGaN barrier layer, 24b InAlGaN well layer, 24 InAlGaN light emitting layer, 25 p-type Al _0.30 Ga _0.70 N layer, 26 p-type Al _0.18 Ga _0.82 N layer.

Claims (4)

Forming a first conductivity type Al _x1 Ga _1-x1 N layer (0 ≦ x1 ≦ 1) on the first main surface side of the nitride semiconductor substrate;
Forming a light emitting layer containing an InAlGaN quaternary mixed crystal on the Al _x1 Ga _1-x1 N layer of the first conductivity type;
Forming a second conductivity type Al _x2 Ga _1-x2 N layer (0 ≦ x2 ≦ 1) on the light emitting layer;
And a step of removing the nitride semiconductor substrate after forming the second conductivity type Al _x2 Ga _1-x2 N layer.   The method for manufacturing a light-emitting element according to claim 1, wherein the nitride semiconductor substrate is a GaN substrate. The method for manufacturing a light emitting element according to claim 1, wherein the nitride semiconductor substrate is an Al _x Ga _1-x N substrate (0 <x ≦ 1). A first conductivity type Al _x1 Ga _1-x1 N layer (0 ≦ x1 ≦ 1) and a second conductivity type Al _x2 Ga ₁ located on the first conductivity type Al _x1 Ga _1-x1 N layer. _-x2 N layer (0 ≦ x2 ≦ 1) and the first conductivity type Al _x1 Ga _1-x1 N layer and the second conductivity type Al _x2 Ga _1-x2 N layer, And a light emitting layer containing crystals,
A light emitting device having no nitride semiconductor layer farther from the first conductivity type Al _x1 Ga _{1 -x1} N layer when viewed from the light emitting layer.

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