JP2007095786A - Group iii nitride-based compound semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the electrostatic withstand voltage of a group III nitride-based compound semiconductor light emitting element. <P>SOLUTION: When an about 2 μm-thick GaN layer is formed on an AlN buffer layer formed by sputtering, its surface has unevenness of about 0.9 nm in average. When the GaN layer is doped with a donor, the unevenness is not so improved. In contrast, when the GaN layer is doped with an acceptor, the unevenness is found to be improved to about 1/2. The improvement also improves the electrostatic withstand voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a group III nitride compound semiconductor light emitting device.

  Group III nitride compound semiconductor light emitting devices are currently required to have improved electrostatic withstand voltage. On the other hand, when forming a group III nitride compound semiconductor light emitting device on a sapphire substrate, a technique of forming an AlN buffer layer by sputtering and then epitaxially growing it has been studied.

  The inventors of the present invention have found that when an AlN buffer layer is formed on a sapphire substrate by sputtering, and then a GaN layer is formed without a dopant, a strong fluorescence phenomenon occurs due to photoluminescence. On the other hand, when the AlN buffer layer was formed by MOVPE, even if a GaN layer was formed without a dopant on the AlN buffer layer, the fluorescence phenomenon due to photoluminescence hardly occurred as compared with the case where the AlN buffer layer was formed by sputtering.

  The present inventors have repeatedly studied to improve the surface morphology of the GaN layer formed after forming the AlN buffer layer by sputtering, and completed the present invention.

  The invention according to claim 1 includes a sapphire substrate, a buffer layer formed thereon, and an n-type layer made of a group III nitride compound semiconductor doped with a donor and having an n-electrode formed thereon. A group III nitride compound semiconductor light-emitting device comprising a group III nitride compound semiconductor layer doped with an acceptor between a buffer layer and an n-type layer It is.

  The invention according to claim 2 is characterized in that the buffer layer is an AlN layer formed by sputtering.

  When a GaN layer having a thickness of about 2 μm is formed on an AlN buffer layer formed by sputtering, the surface has irregularities of about 0.9 nm on average. When the GaN layer is doped with a donor, the unevenness is not improved so much. On the other hand, it has been found that when the GaN layer is doped with an acceptor, the unevenness is improved to about 1/2. This improvement also improves the electrostatic withstand voltage.

Although not a semiconductor material of the semiconductor light-emitting device is limited to be applied to the present invention, a semiconductor light-emitting device when composed of a group III nitride semiconductors, the semiconductor layer to form at least Al _x Ga _y IIn Group III nitride compounds composed of binary, ternary or quaternary semiconductors represented by _1-xy (N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1)) It can be formed of a semiconductor, etc. In addition, some of these group III elements may be replaced by boron (B) and thallium (Tl), and part of nitrogen (N) may be phosphorus (P). , Arsenic (As), antimony (Sb), and bismuth (Bi) may be substituted.

  Further, when an n-type group III nitride compound semiconductor layer is formed using these semiconductors, Si, Ge, Se, Te, C, etc. are added as n-type impurities, and p-type impurities are used as p-type impurities. Zn, Mg, Be, Ca, Sr, Ba and the like can be added.

  In addition, as a substrate for crystal growth of these semiconductor layers, sapphire, spinel, Si, SiC, ZnO, MgO, a group III nitride compound single crystal, or the like can be used.

  As a method for crystal growth of these semiconductor layers, molecular beam vapor phase epitaxy (MBE), metal organic vapor phase epitaxy (MOVPE), halide vapor phase epitaxy (HVPE) and the like are effective.

  Hereinafter, the present invention will be described based on specific examples. However, the present invention is not limited to the following examples.

  First, the influence of the dopant was examined as follows. Using a DC magnetron sputtering apparatus on a surface of a 300 μm thick sapphire substrate, a high-purity metallic aluminum and nitrogen gas are used as raw materials, and a reactive sputtering method is performed at a substrate temperature of 430 ° C. An AlN buffer layer was formed. Next, a gallium nitride layer was formed to a thickness of 2 μm by MOVPE. At this time, trimethylgallium was formed at a growth rate of ˜70 nm / min.

When the gallium nitride layer was doped with Mg at 2 × 10 ¹⁸ / cm ³ , when Si was doped at 2 × 10 ¹⁸ / cm ³ , the surface irregularities when nothing was doped were observed. In the case of 0.49 nm on average, in the case of Si doping, an average of 0.67 nm was observed, and in the case of nothing being doped, an average of 0.86 nm was observed. Thus, when the GaN layer is formed on the sputtered AlN buffer layer, the surface unevenness is most suppressed when Mg as an acceptor is doped.

The light emitting diode having the configuration shown in FIG. 1 was formed, and the electrostatic withstand voltage was measured. On a sapphire substrate 101, a sputtered AlN buffer layer 102, a 2 μm thick i-GaN layer 103 doped with Mg 2 × 10 ¹⁸ / cm ³ , and a 2.5 μm thick silicon (Si) 5 × 10 ¹⁸ / An n-type contact layer 104 (high carrier concentration n ⁺ layer) made of GaN doped with cm ³ is formed.

On this n-type contact layer 104, an undoped GaN layer 105a having a thickness of 0.3 μm and an n-type GaN layer 105b doped with 3 × 10 ¹⁸ / cm ³ of silicon (Si) having a thickness of 30 nm are formed. Yes. An n-side superlattice layer 106, a light emitting layer 107, and a p-side superlattice layer 108 are formed thereon. Further thereon, a layer 109 made of 0.3 μm-thick undoped Al _0.05 Ga _0.95 N, a p-GaN layer 110 doped with 80 nm-thick magnesium (Mg) at 1 × 10 ²⁰ / cm ³ , magnesium ( A p ⁺ -GaN layer 111 having a thickness of 20 nm doped with 2 × 10 ²⁰ / cm ^{3 of} Mg) is formed.

The n-side superlattice layer 106 includes 10 cycles by repeating an In _x Ga _1-x N layer (0.06 ≦ x ≦ 0.14) having a thickness of 2 to 5 nm and an n-GaN layer having a thickness of 3 to 6 nm. This is a superlattice layer.

Each of the light emitting layers 107 is formed of an undoped layer, and includes 3 nm thick In _0.25 Ga _0.75 N, a low temperature grown GaN 2 nm thick film, and a high temperature grown 4 nm thick Al _0.05 Ga _0.95 N film. For 5 cycles, further 3 nm thick In _0.25 Ga _0.75 N, low temperature grown GaN with a thickness of 2 nm, and high temperature grown GaN with a thickness of 2.5 nm.

The p-side superlattice layer 108 is formed of an undoped Al _x Ga _1-x N layer (0.05 ≦ x ≦ 0.4) with a thickness of 2.5 nm, and then grown at a low temperature of 840 ° C. or lower to form magnesium (Mg). Of 2 × 10 ¹⁹ / cm ³ -doped In _x Ga _1-x N (0.05 ≦ x ≦ 0.12) doped with 2 × 10 ¹⁹ / cm ^{3 and} 2 × 10 ¹⁹ / cm ³ doped with magnesium (Mg) The formed Al _x Ga _1-x N layer (0.25 ≦ x ≦ 0.4) was repeated 2.5 times to form a superlattice layer having a total thickness of 25 nm.

  The p electrode is composed of an ITO electrode 120 having a film thickness of about 300 nm on the p + layer 111, and the n electrode 140 has a vanadium layer 141 having a film thickness of about 20 nm and an aluminum layer 142 having a film thickness of about 2 μm on the n + layer. Consists of. In addition, the upper part of the device was covered with a silicon dioxide insulating film 130 except for the connection portion.

  A large number of light emitting elements 100 having such a structure were formed on one wafer and separated as individual chips, and when an electrostatic withstand voltage of −1000 V was applied, 85% survived.

[Comparative example]
In the above embodiment, the i-GaN layer 103 having a thickness of 2 μm and the n-type contact layer 104 made of GaN having a thickness of 2.5 μm are excluded from the configuration of the n-type contact layer 104 except for the i-GaN layer 103. For comparison, the electrostatic withstand voltage was measured for a light-emitting element formed in the same manner except that the thickness was 4.5 μm. The survival rate was 25% when -1000 V was applied.

(Modification)
The present invention is not limited to the above embodiments, and various other modifications are possible. For example, a GaN-based semiconductor layer is used as a group III nitride compound semiconductor element, but of course, a layer composed of Ga _x In _1-x N or the like, or any other ternary to quaternary system with any mixed crystal ratio. AlGaInN may also be used. More specifically, _{"Al x Ga y In 1-xy} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ x + y ≦ 1) " consisting formula ternary represented (GaInN, AlInN, AlGaN) or quaternary (AlGaInN) group III nitride compound semiconductors can also be used. Further, a part of N of the compound may be substituted with a group V element such as P or As.

Sectional drawing which shows the structure of the light emitting element 100 which concerns on Example 2. FIG.

Explanation of symbols

101: sapphire substrate 102: sputtered AlN buffer 103: i-GaN: Mg layer 104: n ⁺ -GaN layer 105a: undoped GaN layer 105b: n-GaN: Si layer 106: n-side superlattice layer 107: MQW light emitting layer 108 : P-side superlattice layer 109: undoped AlGaN layer 110: p-GaN: Mg layer 111: p ⁺ -GaN: Mg layer

Claims (2)

A group III nitride compound semiconductor light-emitting device comprising a sapphire substrate, a buffer layer formed thereon, and a group III nitride compound semiconductor doped with a donor, and an n-type layer on which an n electrode is formed In
A group III nitride compound semiconductor light emitting device having a group III nitride compound semiconductor layer doped with an acceptor between the buffer layer and the n-type layer. The group III nitride compound semiconductor light emitting device according to claim 1, wherein the buffer layer is an AlN layer formed by sputtering.