JP2009049179A - Manufacturing method for group iii nitride compound semiconductor, and light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a group III nitride compound semiconductor such that a rugged part is buried into an epitaxial growth substrate, through a growth in the longitudinal direction, forming a light-emitting element having the rugged part for improvement of the light pick-up performance. <P>SOLUTION: A buried n-GaN:Si layer is made grown via an AlN buffer layer on a sapphire substrate having a rugged part. For comparison, a substrate having a rugged part with an i-GaN layer made grown without adding Si and a substrate having no rugged part with the i-GaN layer made grown without adding Si are prepared. The top face of an epitaxial film is processed with hydrogen chloride (HCl) gas to convert a threading dislocation into a pit. In the case where the n-GaN:Si layer is made grown on the substrate having a rugged part (1. C), many pits are formed as in the case where the i-GaN layer is made grown on the substrate having no rugged part (1. A), but the density is uniform, never being concentrated. In the case where the i-GaN layer is made grown on the substrate having a rugged part (1. B), dislocation is concentrated on the upper side of a convex portion on the substrate to form a large pit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for producing a group III nitride compound semiconductor and a light emitting device. In the present application, the group III nitride compound semiconductor is a semiconductor represented by Al _x Ga _y In _1-xy N (where x, y, and x + y are all 0 or more and 1 or less), n-type / p-type, etc. For which any element is added. Furthermore, it includes those in which a part of the composition of the group III element and the group V element is substituted with B, Tl; P, As, Sb, Bi.

In order to improve the light extraction of the group III nitride compound semiconductor light emitting device, there is a technique of providing irregularities on the side of the epitaxial growth substrate on which the group III nitride compound semiconductor is formed. The following Patent Documents 1 and 2 are techniques for filling the concave portion by lateral growth.
JP 2002-280609 A JP 2002-280611 A

  When GaN containing no impurities is grown when filling the concave and convex portions, voids (gap) are generated in the vicinity of the concave and convex portions. Alternatively, the dislocations bend irregularly, so that a region having a high dislocation density and a region having a low dislocation density may be generated in the crystal film plane. In this case, the crystal quality of the light emitting layer is not uniform, resulting in uneven light emission, a decrease in color purity, or an increase in the half width of the emission spectrum. Excessively, the luminous efficiency is lowered and the electrostatic withstand voltage characteristic is deteriorated.

  Accordingly, an object of the present invention is to prevent the generation of voids (gap) when filling a concave portion with an epitaxial growth layer when using a concavo-convex substrate for light extraction improvement, and to reduce dislocation density due to dislocation bending. Is to prevent.

The invention according to claim 1 is a donor having a group III nitride compound semiconductor of 1 × 10 ¹⁷ / cm ³ or more and less than 1 × 10 ¹⁹ / cm ³ through a buffer layer on the surface of the substrate on which irregularities are formed. This is a method for producing a group III nitride compound semiconductor, characterized in that dislocations are formed by longitudinal epitaxial growth extending straight in the thickness direction while adding.
The invention according to claim 2 is characterized in that the donor is silicon (Si).
The invention according to claim 3 is characterized in that the amount of silicon (Si) added is 1 × 10 ¹⁸ / cm ³ or more and 8 × 10 ¹⁸ / cm ³ or less.
The invention according to claim 4 is characterized in that the group III nitride compound semiconductor is gallium nitride (GaN).
The invention according to claim 5 is characterized in that the substrate is an insulating substrate.
The invention according to claim 6 is characterized in that the concave and convex portions formed on the substrate are formed by forming the concave portion by etching.

In the invention according to claim 7, a substrate having irregularities formed on the surface, a buffer layer, and a donor of 1 × 10 ¹⁷ / cm ³ or more and less than 1 × 10 ¹⁹ / cm ³ are added, and the dislocation is in the thickness direction. A group III nitride compound semiconductor light-emitting device comprising a group III nitride compound semiconductor layer extending straight.
The invention according to claim 8 is characterized in that there is no void at the boundary between the group III nitride compound semiconductor layer and the buffer layer or the substrate.
The invention according to claim 9 is characterized in that the group III nitride compound semiconductor layer has no significant difference in threading dislocation density between the upper portion of the concave portion and the upper portion of the convex portion of the surface of the substrate.

  As a donor of a group III nitride compound semiconductor, an IV valent element is generally used. For example, silicon (Si). Substituting IV-valent elements for positions such as III-valent gallium (Ga) promotes vertical growth. That is, so-called lateral growth hardly occurs during epitaxial growth. Then, the dislocation does not bend, and extends straight in the film thickness direction. In addition, voids are less likely to occur near the unevenness of the epitaxial growth substrate.

According to the method for producing a group III nitride compound semiconductor according to the present invention, for example, when an n-type group III nitride compound semiconductor is formed to a thickness of 2 to 5 μm, threading dislocations are related to the position of the unevenness of the substrate. It is distributed uniformly and becomes 1 × 10 ⁸ pieces / cm ² to 1 × 10 ¹⁰ pieces / cm ² . Therefore, when a light emitting element is formed on the epitaxial film, a region having a high dislocation density and a region having a small dislocation density do not occur in the crystal film surface, so that the crystal quality of the light emitting layer is uniform, light emission unevenness does not occur, and color purity is also improved. It does not decrease, and further, the half width of the emission spectrum does not increase. Furthermore, the light emission efficiency is improved and the electrostatic withstand voltage characteristic is improved.

As the donor, it is simplest to use silicon (Si), but other IV-valent elements may be used.
If the added amount of the donor is less than 10 ¹⁷ / cm ³ , the effect is not sufficient, and if it exceeds 1 × 10 ¹⁹ / cm ³ , the donor-added film becomes cloudy and does not become a single crystal.

Concavities and convexities formed on the epitaxial growth substrate can be easily formed by etching using an etching mask formed in a desired shape. However, for example, a method of mechanically processing and then performing surface treatment may be used.
It is preferable that both the top of the uneven step and the bottom of the step are surfaces parallel to the main surface of the epitaxial growth substrate before formation of the unevenness. The side surfaces of the uneven step may be perpendicular to the main surface of the epitaxial growth substrate, but may not be perpendicular.
The shape of the circumference (contour) of the top surface of the step may be arbitrary, but may be a regular hexagon, for example.
The pitch when the top surface of the step is an island shape or a stripe shape may be arbitrarily designed. For example, it is preferable that the top surface of the step is a polygon inscribed in a circle having a diameter of 0.5 to 10 μm, or the width of the top surface and the bottom portion of the stripe shape are 0.5 to 10 μm.
The height difference between the top surface and the bottom of the step is preferably about 0.1 to 2 μm, and preferably 0.5 to 1 μm.

  Any substrate may be used as the epitaxial growth substrate. In the case of using an insulating substrate, sapphire, zinc oxide, or spinel is particularly preferable. In the case of using a conductive substrate, silicon or SiC is particularly preferable. These are rich in papers and other reports, can be used as they are, and are simple.

The present invention relates to a method for producing a group III nitride compound semiconductor, in which an epitaxial growth substrate has irregularities, and a group III nitride compound semiconductor to which a donor is added via a buffer layer is formed by vertical growth. The other conditions are not limited at all.
Furthermore, the manufacturing conditions, the layer configuration, the electrode configuration, and other additional configurations when forming an arbitrary device, particularly a light emitting device, on the group III nitride compound semiconductor to which the donor is added are not limited at all.
For example, when forming a light emitting element, a single layer, a single quantum well structure (SQW), a multiple quantum well structure (MQW), or any other configuration can be adopted for the light emitting layer or the active layer. For example, when a clad layer is provided on the p side and / or n side of the light emitting layer or the active layer, one or both of the clad layers may be composed of multiple layers. In the laser, a guide layer or a current confinement structure may be provided, or an insulating layer may be provided on an arbitrary surface or inside. Furthermore, a layer for improving electrostatic withstand voltage may be provided.
For example, when a light emitting element is formed on an insulating substrate such as a sapphire substrate, a so-called face up or flip chip configuration may be used. Naturally, as each electrode, a translucent electrode or a highly reflective electrode can be adopted at any place.

First, in order to obtain data showing the effect of the present invention, a group III nitride compound semiconductor was formed as follows.
The sapphire substrate 10 provided with unevenness for light extraction on the surface on the epitaxial growth side was baked at 1160 ° C. or higher in a hydrogen atmosphere. The concaves and convexes are formed by forming a regular hexagon inscribed in a circle having a diameter of about 2 μm with a convex part interspersed at a pitch of about 2 μm and a bottom part (concave part) of the step, and forming a concave part by etching. The side surface of the step is not vertical but has an inclination of about 80 degrees in the direction in which the area of the upper surface of the convex portion becomes narrower. The process difference of the unevenness was about 0.8 μm.
Next, the substrate temperature was lowered to 400 ° C., and an AlN buffer layer was grown by about 15 nm. The AlN buffer layer was formed not only on the top surface of the convex portion and the bottom surface (concave portion) of the step, but also on the side surface of the step.
Next, the substrate temperature is increased to 1050 to 1150 ° C., and H ₂ as carrier gas is 36 L / min, ammonia (NH ₃ ) is 15 L / min, trimethylgallium (TMG) is 5 × 10 ⁻⁴ mol / min, H ₂ gas. Silane (SiH ₄ ) diluted to 1.4 ppm by the above was supplied for 60 minutes, and the buried n-GaN: Si layer 11 was grown. The embedded n-GaN: Si layer 11 was formed to a thickness of about 4 μm from the bottom (recessed portion) of the step.

By changing the supply amount of silane when forming the n-GaN: Si layer 11, the n-GaN: Si layer 11 in which the addition amount of silicon was changed was formed as follows.
Example 1-1: Addition amount of silicon 5 × 10 ¹⁷ / cm ³ .
Example 1-2: Addition amount of silicon 3 × 10 ¹⁸ / cm ³
Example 1-3: Addition amount of silicon 5 × 10 ¹⁸ / cm ³ .
Comparative Example 1-1: Addition amount of silicon 1 × 10 ¹⁹ / cm ³ .
Comparative Example 1-2: No silicon was added (i-GaN layer 21).
Furthermore, as Comparative Example 1-3, a sapphire substrate 20 not provided with unevenness was prepared by forming a GaN layer (i-GaN layer 22) to which silicon was not added with a thickness of 4 μm through a buffer layer.

Next, in order to compare the density and distribution of threading dislocations reaching the epitaxial film surfaces of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3, the epitaxial film surface was treated with hydrogen chloride (HCl) gas. The threading dislocations were converted into pits for comparison. The results were as follows.
Example 1-1: When the amount of silicon added was 5 × 10 ¹⁷ / cm ³ , many pits were formed as in Comparative Example 1-3 shown below, but the density was uniform and concentrated. There was no.
Example 1-2: When the amount of silicon added was 3 × 10 ¹⁸ / cm ³ , many pits were formed as in Comparative Example 1-3 shown below, but the density was uniform and concentrated. There was no.
Example 1-3: When the amount of silicon added was 5 × 10 ¹⁸ / cm ³ , many pits were formed as in Comparative Example 1-3 shown below, but the density was uniform and concentrated. There was no.
Comparative Example 1-1: When the addition amount of silicon was 1 × 10 ¹⁹ / cm ³ , the surface was clouded before the HCl treatment, and a single crystal with good crystallinity was not obtained.
Comparative Example 1-2: When silicon was not added, dislocations concentrated above the convex portions of the substrate, resulting in large pits. The portion where large pits were not formed had a relatively low pit density.
Comparative Example 1-3: In the case of a GaN layer without addition of silicon on a sapphire substrate without unevenness, a large number of pits were formed, but the density was uniform and did not concentrate.

  FIG. 1 shows three examples of pits (black portions in the figure) after hydrogen chloride (HCl) gas treatment. Both are 10 μm square, and FIG. A is Comparative Example 1-3, FIG. B is Comparative Example 1-2, FIG. C conceptually shows the result of Example 1-2. Examples 1-1 and 1-3 are also shown in FIG. A pit similar to C was formed.

Moreover, the transmission electron microscope (TEM) photograph of the vertical cross section was image | photographed about Comparative Example 1-3, Comparative Example 1-2, and Example 1-2. FIG. A is Comparative Example 1-3, FIG. B is Comparative Example 1-2, FIG. C conceptually shows the TEM photograph of Example 1-2. FIG. In Comparative Example 1-2 of B, voids (voids) were observed at the growth start portion, and dislocations were concentrated above the convex portions of the sapphire substrate 10. This corresponds to the state of the pit after the hydrogen chloride (HCl) gas treatment. That is, when the silicon of Comparative Example 1-2 is not added, it is considered that the lateral growth is the main in the epitaxial growth of the i-GaN layer 21, and the dislocations are bent and concentrated above the convex portion of the substrate surface. That is, there was a significant difference in the density of threading dislocations above the convex portion and the concave portion of the sapphire substrate 10.
On the other hand, FIG. In Example 1-2 according to the present invention of C, since silicon was appropriately added, in the epitaxial growth of the n-GaN: Si layer 11, the vertical growth was the main, dislocations were not bent, and the surface of the sapphire substrate 10 was uneven. Regardless, it is considered that the wafer was uniformly formed on the entire wafer. This is because the i-GaN layer 22 not added with silicon is epitaxially grown on the surface of the sapphire substrate 20 having no irregularities. The same results as in Comparative Example 1-3 of A were obtained.

From the examination of the above Examples and Comparative Examples, the amount of donor added is 1 × 10 ¹⁷ / cm ³ or more and less than 1 × 10 ¹⁹ / cm ³ , preferably 1 × 10 ¹⁸ / cm ³ or more and 8 × 10 ¹⁸ / cm ³ or less. It turns out that is preferable.

A blue light emitting diode having an emission wavelength of 465 nm was formed on the sapphire substrate 10 having irregularities formed in Example 1-2, using the n-GaN: Si layer 11 as an n contact layer (Example 2).
Similarly, an n-GaN: Si contact layer 11 ′ is formed on the i-GaN layer 21 on the uneven sapphire substrate 10 formed in Comparative Example 1-2, and the blue light emission wavelength is also 465 nm. A light emitting diode was formed (Comparative Example 2). At this time, the thickness of the n-contact layer 11 of Example 2 is made equal to the total thickness of the two layers of the i-GaN layer 21 and the n-GaN: Si contact layer 11 ′ of Comparative Example 2, and The structure of the light emitting element formed above was made completely the same. This is shown in FIG. FIG. 2. A is sectional drawing which shows the outline of a structure of the blue light emitting diode 100 which concerns on Example 2, FIG. B is a cross-sectional view schematically illustrating a configuration of a blue light emitting diode 900 according to Comparative Example 2. FIG.

The characteristics of the blue light emitting diodes according to Example 2 and Comparative Example 2 were measured. This is shown in FIG.
FIG. A is a graph comparing the brightness when 20 mA is applied to each blue light emitting diode according to Example 2 and Comparative Example 2. FIG. The brightness of the blue light emitting diode of Example 2 was improved by about 13% compared to the blue light emitting diode of Comparative Example 2.
FIG. B is a graph comparing the wavelength width (full width at half maximum) of the emission spectrum when 20 mA is applied to each blue light emitting diode according to Example 2 and Comparative Example 2, which is half the maximum luminance. In the blue light emitting diode of Example 2, the full width at half maximum of the wavelength spectrum was reduced by about 7% compared to the blue light emitting diode of Comparative Example 2, and the color purity was improved.
FIG. C is an electrostatic withstand voltage characteristic of each blue light emitting diode according to Example 2 and Comparative Example 2, and is a diode obtained from one wafer and having a reverse current of 2 μA or more when a reverse bias of 5 V is applied. It is the graph which compared the ratio (failure ratio). The failure rate of the blue light emitting diode of Example 2 was 11%, which was a significant improvement over the failure rate of 39% of the blue light emitting diode of Comparative Example 2.

The conceptual diagram which shows three examples of the surface pits after processing the group III nitride compound semiconductor surface which concerns on an Example and a comparative example with HCl. The conceptual diagram which shows three examples of the TEM photograph of the group III nitride compound semiconductor which concerns on an Example and a comparative example. Sectional drawing which shows the outline of a structure of the blue light emitting diode which concerns on Example 2 and Comparative Example 2. FIG. The graph which shows the characteristic of the blue light emitting diode which concerns on Example 2 and Comparative Example 2. FIG.

Explanation of symbols

10: Epitaxially grown epitaxial substrate having irregularities 11: Group III nitride compound semiconductor layer (n-GaN: Si layer) with added donor
21: Group III nitride compound semiconductor layer without addition of impurities (i-GaN layer)

Claims (9)

On the substrate surface on which the irregularities are formed,
Through the buffer layer,
A group III nitride compound semiconductor is formed by longitudinal epitaxial growth in which dislocations extend straight in the thickness direction while adding a donor of 1 × 10 ¹⁷ / cm ³ or more and less than 1 × 10 ¹⁹ / cm ^3. A method for producing a group III nitride compound semiconductor. The method for producing a group III nitride compound semiconductor according to claim 1, wherein the donor is silicon (Si). ^{3. The} method for producing a group III nitride compound semiconductor according to claim 2, wherein the amount of silicon (Si) added is 1 × 10 ¹⁸ / cm ³ or more and 8 × 10 ¹⁸ / cm ³ or less. The method for producing a group III nitride compound semiconductor according to any one of claims 1 to 3, wherein the group III nitride compound semiconductor is gallium nitride (GaN). The method for producing a group III nitride compound semiconductor according to any one of claims 1 to 4, wherein the substrate is an insulating substrate. The group III nitride compound semiconductor manufacturing method according to any one of claims 1 to 5, wherein the concave and convex portions formed on the substrate are formed by forming a concave portion by etching. Method. A substrate with irregularities formed on the surface;
A buffer layer,
A group III comprising a group III nitride compound semiconductor layer to which a donor of 1 × 10 ¹⁷ / cm ³ or more and less than 1 × 10 ¹⁹ / cm ³ is added and dislocations extend straight in the thickness direction Nitride compound semiconductor light emitting device. 8. The group III nitride compound semiconductor light-emitting element according to claim 7, wherein no void is formed at a boundary between the group III nitride compound semiconductor layer and the buffer layer or the substrate. 9. The group III nitride compound semiconductor layer according to claim 7, wherein there is no significant difference in threading dislocation density between the upper portion of the concave portion and the upper portion of the surface of the substrate. Group III nitride compound semiconductor light emitting device.

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