JP2004363349A - Nitride system compound semiconductor device and light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce dislocation density in the nitride system compound semiconductor device. <P>SOLUTION: A first buffer layer 12, a second buffer layer 14, an SLS layer 16, an MQW light emitting layer 18, an SLS layer 20, an electrode forming layer 22, a p-type electrode 24, and an n-type electrode 26 are formed on a substrate 10. The dislocation density of the MQW light emitting layer 18 is reduced and absorption of light can also be suppressed by using the AINP formed under low temperature as the first buffer layer 12 and the AlNP formed under high temperature as the second buffer layer 14. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

表において、「ＬＴ」は低温形成であることを示し、「ＨＴ」は高温形成であることを示す。例えば、表１のサンプルＡは第１バッファ層（低温バッファ層）１２としてＡｌＮ_０．９５Ｐ_０．０５を用い、第２バッファ層１４（高温バッファ層あるいは下地層）としてＡｌＮ_０．９９Ｐ_０．０１を用いたサンプルである。Ｘ＝０．０５（組成比５％）、ｙ＝０．０１（組成比１％）の場合である。また、サンプルＢは第１バッファ層（低温バッファ層）としてサンプルＢと同一のＡｌＮ_０．９５Ｐ_０．０５を用い、第２バッファ層１４（高温バッファ層あるいは下地層）としてＡｌＮを用いたサンプルである。ｙ＝０（組成比０％）の場合である。発光強度はサンプルＥの発光強度を基準とした相対値である。サンプルＥはＧａＮを第１バッファ層１２及び第２バッファ層１４に用いたものである。各サンプルの発光強度は複数（９個）の平均値で示してある。サンプルＥの発光強度は、注入電流２０ｍＡで約１ｍＷである。
【００２１】
サンプルＥの転位密度は約５×１０^８ｃｍ^−２であり、全てのサンプルの中で最も低い。しかしながら、ＧａＮはＭＱＷ層１８から射出した光を吸収してしまうため光取り出し効率は低い。サンプルＡとサンプルＥを比較すると、転位密度はサンプルＡの方が高いにもかかわらず発光強度はサンプルＥの５．２倍となっている。これは、サンプルＡのバッファ層であるＡｌＮＰがＭＱＷ層１８からの光をほとんど吸収しないからである。さらに、ＡｌＮＰの表面の凹凸によりＭＱＷ層１８からの光を散乱しているためと考えられる。サンプルＢ及びサンプルＣもサンプルＥと比べるとバッファ層での吸収が低いため相対発光強度はそれぞれ４．５倍、２．５倍となっているが、サンプルＡよりは低い。これは、サンプルＢ及びサンプルＣの場合には、サンプルＡと比べて転位密度が高いためと考えられる。サンプルＤはサンプルＥよりも発光強度が低い。これは、第２バッファ層１４であるＡｌＧａＮ層上に形成したＳＬＳ１６層及びＭＱＷ層１８内の転位密度が高いこと、及びＡｌＧａＮでの光の吸収があるためと考えられる。
【００２２】
このように、第１バッファ層１２としてＡｌＮ_１−ｘＰ_ｘを用い、第２バッファ層としてＡｌＮ_１−ｙＰ_ｙを用いることで、発光強度を著しく向上させることができ、特に第１バッファ層１２及び第２バッファ層１４として共にＡｌＮＰを用いることで、低転位密度かつ低光吸収を実現し、結果として光取出効率の高いＬＥＤを得ることができる。
【００２３】
以下、第１バッファ層１２と第２バッファ層１４について、さらに詳細に説明する。
【００２４】
図２には、基板１０、第１バッファ層１２及び第２バッファ層１４が示されている。第１バッファ層１２は低温で形成されたＡｌＮＰであり、第２バッファ層は高温で形成されたＡｌＮＰである。具体的には、以下のようにして形成される。
【００２５】
まず、ＭＯＣＶＤ装置内にサファイアｃ面基板１０を設置し、水素雰囲気中で１１５０℃にて熱処理する。そして、温度５００℃でＡｌＮＰを形成して第１バッファ層１２とする。第１バッファ層１２の厚さは約２０ｎｍである。層の厚さ及び成長温度は一例であり、層の厚さが１０〜５０ｎｍ、成長温度が４００℃〜７００℃の範囲内であれば同様の層が形成される。その後、温度を１０８０℃まで上げ、ＡｌＮＰを形成して第２バッファ層１４とする。第２バッファ層１４の厚さは約２μｍである。第１バッファ層１２及び第２バッファ層１４のＡｌＮＰは、トリメチルアルミニウム、アンモニア、フォスフィンを原料ガスとしてＭＯＣＶＤ法により形成される。各原料ガスの流量は、トリメチルアルミニウム１０〜１５０μｍｏｌ／ｍｉｎ、アンモニア１５ＳＬＭ（Ｓｔａｎｄａｒｄ Ｌｉｔｅｒ ｐｅｒ ｍｉｎｕｔｅｓ：基準流量単位）、フォスフィン１〜１００ｓｃｃｍである。成長中の反応炉内の圧力は１００Ｔｏｒｒである。比較のため、第１バッファ層１２として低温でＧａＮあるいはＡｌＮを形成し、その後第２バッファ層１４としてＡｌＮＰを形成した。サンプル構成を以下に示す。
【００２６】
サンプルα：基板／ＬＴ−ＡｌＮＰ／ＨＴ−ＡｌＮＰ
サンプルβ：基板／ＬＴ−ＧａＮ／ＨＴ−ＡｌＮＰ
サンプルγ：基板／ＬＴ−ＡｌＮ／ＨＴ−ＡｌＮＰ
サンプルα及びサンプルγにおいては、第２バッファ層１４であるＨＴ−ＡｌＮＰの表面は鏡面であるが、サンプルβの表面は白濁している。
【００２７】
ＡｌＮＰ中のＰ組成は、原料ガス流量と成長温度に依存する。同じ原料ガス流量であれば、ＬＴ−ＡｌＮＰ中のＰ組成はＨＴ−ＡｌＮＰ中のＰ組成よりも大幅に大きくなる。例えば、フォスフィン流量が５０ｓｃｃｍの場合、ＬＴ−ＡｌＮＰ中のＰ組成比は約１０％であり、ＨＴ−ＡｌＮＰ中のＰ組成比は約１％となり、ＨＴ−ＡｌＮＰ中のＰ組成比はＬＴ−ＡｌＮＰ中のＰ組成比の約１／１０となる。ＨＴ−ＡｌＮＰの成長温度を１０８０℃から１０００℃まで下げると、ＨＴ−ＡｌＮＰ中のＰ組成比は１．５％となる。ＡｌＮＰ中のＰ組成比は、例えばＳＩＭＳ（二次イオン質量分析計）により測定される。サンプルαを組成比で示すと、基板／ＬＴ−ＡｌＮ_０．９Ｐ_０．１／ＨＴ−ＡｌＮ_０．９９Ｐ_０．０１であり、サンプルγを組成比で示すと、基板／ＬＴ−ＡｌＮ／ＨＴ−ＡｌＮ_０．９９Ｐ_０．０１である。これらのサンプルα、γの転位密度を平面ＴＥＭ（透過電子顕微鏡）で測定すると、サンプルαは約５×１０^９ｃｍ^−２、サンプルγは約５×１０^１０ｃｍ^−２である。従って、転位密度低減の観点からはサンプルαの方が望ましいことが分かる。
【００２８】
次に、第２バッファ層１４としてのＨＴ−ＡｌＮＰ中のＰ組成比を約１％に維持しつつ、第１バッファ層１２としてのＬＴ−ＡｌＮＰ中のＰ組成比を変化させて転位密度を測定した。
【００２９】
図３には、ＬＴ−ＡｌＮＰ中のＰ組成比に対する転位密度の変化が示されている。転位密度は、ＬＴ−ＡｌＮＰ中に０．５％程度のＰを添加することで急減に減少し、さらにＰ組成の増大とともに減少していく。しかし、あまりにＰ組成が高いと転位密度は逆に増大してしまう。ＬＴ−ＡｌＮＰの最適なＰ組成は、その上に形成されるＨＴ−ＡｌＮＰのＰ組成に依存するものの、本実施形態では最適なＰ組成比は約５％である。本実施形態における最適な組成比を例示すると以下の通りである。
【００３０】
基板１０／第１バッファ層（ＬＴ−ＡｌＮ_０．９５Ｐ_０．０５）１２／第２バッファ層（ＨＴ−ＡｌＮ_０．９９Ｐ_０．０１）
なお、ＨＴ−ＡｌＮ_０．９９Ｐ_０．０１のバンドギャップエネルギは室温で６ｅＶ程度と見積もられる。
【００３１】
図４には、基板１０、第１バッファ層１２、第２バッファ層１４の他の構成が示されている。第２バッファ層１４としてＨＴ−ＡｌＮあるいはＨＴ−ＡｌＧａＮを用い、第１バッファ層１２としてＬＴ−ＡｌＮＰその他を用いる構成である。具体的な製造方法は、以下の通りである。ＭＯＣＶＤ装置内にサファイアｃ面基板１０を設置し、水素雰囲気中で１１５０℃にて熱処理する。そして、温度５００℃でＡｌＮＰ、ＡｌＮ、ＧａＮを形成して第１バッファ層１２とする。第１バッファ層１２の厚さは約２０ｎｍである。その後、温度を１０８０℃まで上げ、ＡｌＮを形成して第２バッファ層１４とする。第２バッファ層１４の厚さは約２μｍである。ＡｌＮＰは、トリメチルアルミニウム、アンモニア、フォスフィンを原料ガスとしてＭＯＣＶＤ法により形成される。ＡｌＧａＮは、トリメチルアルミニウム、トリメチルガリウム、アンモニアを原料ガスとして形成される。
【００３２】
各サンプルの組成及びＴＥＭで測定した転位密度は以下の通りである。
【００３３】
【表２】

表において、サンプルａは第１バッファ層１２としてＬＴ−ＡｌＮ_０．９５Ｐ_０．０５を形成し、第２バッファ層１４としてＨＴ−ＡｌＮを形成したものである。また、サンプルｄは第１バッファ層１２としてＬＴ−ＡｌＮ_０．９５Ｐ_０．０５を形成し、第２バッファ層１４としてＨＴ−Ａｌ_０．１５Ｇａ_０．８５Ｎを形成したものである。
【００３４】
表からわかるように、Ｐを添加した第１バッファ層１２を用いたサンプルａ及びサンプルｄでは転位密度が１桁程度低い。また、サンプルａの方がサンプルｄよりも転位密度が低く、第１バッファ層１２としてＰを用いた場合、第２バッファ層１４としてＡｌＮ系を用いる場合の方がＡｌＧａＮ系を用いる場合よりも効果が高い。
【００３５】
以上より、第１バッファ層１２としてＬＴ−ＡｌＮＰを用い、第２バッファ層としてＨＴ−ＡｌＮＰあるいはＨＴ−ＡｌＮを用いる（あるいはＨＴ−ＡｌＧａＮを用いる）ことで、転位密度を低減しつつ光の吸収を抑制したＬＥＤを得ることができる。
【００３６】
なお、第２バッファ層１４としてのＨＴ−ＡｌＮＰのＡｌの一部あるいは全部をＧａで置き換えることも可能である。Ａｌの一部あるいは全部をＧａで置き換えると、その成長速度は増大する。一つの例は、基板／ＬＴ−ＡｌＮ_０．９５Ｐ_０．０５／ＨＴ−Ａｌ_０．５Ｇａ_０．５Ｎ_０．９９Ｐ_０．０１である。ＨＴ−ＡｌＧａＮＰの成長温度は９８０℃である。ＨＴ−ＡｌＧａＮＰの成長温度はＡｌＮＰの場合と比べると低い。これは、Ｇａ−Ｐ結合がＡｌ−Ｐ結合に比べて弱いためと考えられる。また、転位密度はＧａの増大とともに若干増大する傾向がある。したがって、Ａｌの一部をＧａで適量だけ置換することが好適である。図５には、この場合の基板１０，第１バッファ層１２、第２バッファ層１４の構成が示されている。
【００３７】
また、ＨＴ−ＡｌＮＰのＡｌの一部をＩｎで置き換えたＨＴ−ＡｌＩｎＮＰも考えられるが、この場合にはＩｎを固相中に取り込むため成長温度を８５０℃以下にする必要があり成長速度が低下する。また、表面荒れも顕著になる。
【００３８】
また、本実施形態において、Ｐを添加する代わりにＡｓを添加してもよい。例えば、基板１０上に第１バッファ層１２としてＬＴ−ＡｌＮＡｓを形成し、第２バッファ層１４としてＡｌＮを形成する。第２バッファ層１４上に図１に示されたＳＬＳ層１６、ＭＱＷ層１８、ＳＬＳ層２０を形成し、さらにｐ型電極２４及びｎ型電極２６を形成してＬＥＤを作製したところ、相対光強度４．０が得られた。Ｐ原子を用いた場合と比較すると光出力は弱いが、Ａｓ原子もＰ原子と同様の効果を生じ得る。
【００３９】
Ｐ原子の代わりにＡｓ原子を用いた構成例を以下に示す。
【００４０】
基板／ＬＴ−ＡｌＮＡｓ／ＨＴ−ＡｌＮＡｓ
基板／ＬＴ−ＡｌＮＡｓ／ＨＴ−ＡｌＮ
基板／ＬＴ−ＡｌＮＡｓ／ＨＴ−ＡｌＧａＮ
基板／ＬＴ−ＡｌＮＡｓ／ＨＴ−ＡｌＧａＮＡｓ
組成比は、例えば基板／ＬＴ−ＡｌＮ_０．９５Ａｓ_０．０５／ＨＴ−ＡｌＮ_０．９９Ａｓ_０．０１である。図６に、この場合の構成例が示されている。
【００４１】
また、本実施形態において、第１バッファ層１２としてＬＴ−ＡｌＮＰを用い、第２バッファ層１４としてＨＴ−ＡｌＮＡｓを用いることも可能である。第１バッファ層１２としてＬＴ−ＡｌＮＡｓを用い、第２バッファ層１４としてＨＴ−ＡｌＮＰを用いることも可能である。
【００４２】
さらに、本実施形態では、第１バッファ層１２及び第２バッファ層１４上にＳＬＳ層や発光層を積層してなるＬＥＤについて説明したが、ＬＥＤ以外の電子デバイスにも適用することが可能である。その一例はＧａＮを電気伝導層としたＦＥＴ等の電子デバイスである。基板上にＡｌＮＰ結晶あるいはＡｌＮＡｓ結晶を成長させて下地層とし、この下地層の上にＧａＮを電気伝導層としたＦＥＴ等を形成することで、転位密度の低減された電子デバイスが得られる。基本構成は、基板／ＡｌＮＰ（あるいはＡｌＮＡｓ）／半導体層であり、基板及び半導体層の材料は任意である。半導体層の転位密度を低減させることで、半導体層の電気特性向上が期待できる。第１バッファ層及び第２バッファ層が一体化されてＡｌＮＰ（ＡｌＮＡｓ）層を構成する。
【００４３】
【発明の効果】
以上説明したように、本発明によれば、転位密度を抑制することができる。また、ＬＥＤ等の発光装置に適用した場合に転位密度を抑制するとともに光の吸収を抑制することができる。
【図面の簡単な説明】
【図１】実施形態のＬＥＤの構成図である。
【図２】第１バッファ層及び第２バッファ層の構成図である。
【図３】ＬＴ−ＡｌＮＰ中のＰ組成比とＨＴ−ＡｌＮＰ中の転位密度の関係を示すグラフ図である。
【図４】第１バッファ層及び第２バッファ層の他の構成図である。
【図５】第１バッファ層及び第２バッファ層のさらに他の構成図である。
【図６】第１バッファ層及び第２バッファ層のさらに他の構成図である。
【符号の説明】
１０ 基板、１２ 第１バッファ層、１４ 第２バッファ層、１６ ＳＬＳ層、１８ ＭＱＷ層、２０ ＳＬＳ層、２２ 電極形成層、２４ ｐ電極、２６ ｎ電極。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nitride-based compound semiconductor device, a light emitting device, and a semiconductor device, and more particularly to an improvement in a buffer layer.
[0002]
[Prior art]
Opto-electronic devices using gallium nitride (GaN) -based compound semiconductors have been developed and put to practical use in fields such as traffic lights, large display devices, and environmental purification using photocatalytic reactions. These use a GaN-based compound semiconductor such as InGaN, GaN, AlGaN, or AlInGaN as a light emitting layer. When the solid composition of the group III element is changed, the band gap energy changes, and the emission wavelength changes accordingly. Also, electronic devices such as FETs using GaN as an electric conductive layer have been produced, and devices utilizing GaN's excellent electric conduction characteristics and temperature characteristics have been developed. However, in most cases, these elements are crystal-grown on a substrate such as sapphire that does not lattice match, so that high-density dislocations occur in the crystal.
[0003]
On the other hand, in a light emitting device having an emission wavelength of 370 nm or less, a structure in which AlInGaN is used as a light emitting layer and the light emitting layer is sandwiched between AlInGaN is generally grown on a GaN buffer layer or AlN buffer layer grown on sapphire or SiC. It is.
[0004]
[Non-patent document 1]
Nishida et al., Proc. 1, September 24-27, 2000, 27a-YH-4
[0005]
[Problems to be solved by the invention]
However, dislocations due to lattice mismatch occur in the GaN buffer layer or the AlN buffer layer formed on the substrate, and these dislocations propagate to the light emitting layer and deteriorate luminous efficiency. The dislocation density generated by using the GaN buffer layer is one order of magnitude lower than that using AlN. However, since GaN absorbs a part of the light emitted from the light emitting layer, the light extraction efficiency is low. descend. Therefore, GaN and AlN as buffer layers each have advantages and disadvantages, and cannot be said to be the best materials.
[0006]
An object of the present invention is to provide a semiconductor device in which dislocation density is suppressed. Another object of the present invention is to provide a light-emitting device in which light absorption is suppressed.
[0007]
[Means for Solving the Problems]
The present invention is a nitride-based compound semiconductor device, comprising: a first buffer layer and a second buffer layer formed on a substrate; and a nitride-based compound semiconductor layer formed on the second buffer layer. One buffer layer is characterized by AlN _1-x P _x (where 0 <x <1). By using AlN _1-x P _x obtained by adding P atoms to AlN as the first buffer layer, the dislocation density of the nitride-based compound semiconductor layer formed thereon is reduced.
[0008]
In the present invention, the second buffer layer preferably _satisfies AlN _{1-y Py} (where 0 ≦ y <1). AlGaN or AlGaNP may be used as the second buffer layer.
[0009]
Further, the present invention is a nitride-based compound semiconductor device formed by forming a first buffer layer and a second buffer layer on a substrate and forming a nitride-based compound semiconductor layer on the second buffer layer, The first buffer layer is characterized by AlN _1-x As _x (where 0 <x <1). By using AlN _1-x As _x obtained by adding As atoms to AlN as the first buffer layer, the dislocation density of the nitride-based compound semiconductor layer formed thereon is reduced.
[0010]
In the present invention, the second buffer _{layer, AlN 1-y} As y (where, 0 ≦ y <1) is preferably set to. AlGaN or AlGaNP may be used as the second buffer layer.
[0011]
The nitride-based compound semiconductor layer formed on the second buffer layer includes an n-type GaN-based layer, a p-type GaN-based layer, and a layer formed between the n-type GaN-based layer and the p-type GaN-based layer. GaN-based light emitting layer. In this case, the nitride-based compound semiconductor device functions as an LED. By using AlNP or AlNAs instead of GaN for the first buffer layer and the second buffer layer, absorption of light from the GaN-based light emitting layer is suppressed.
[0012]
The present invention also relates to a light emitting device using a nitride-based compound semiconductor layer, comprising a substrate, an AlN _1-x P _x low-temperature buffer layer (0 <x <1) formed on the substrate. the _{AlN 1-x P} x low-temperature buffer layer _{AlN 1-y P} y high-temperature buffer layer formed on (where, 0 ≦ y <1) and, formed on the _{AlN 1-y P} y high-temperature buffer layer A first-conductivity-type GaN-based superlattice layer, a GaN-based multilayer quantum well light-emitting layer formed on the first-conductivity-type GaN-based superlattice layer, and a first And a two-conductivity GaN-based superlattice layer. The combination of the AlNP low-temperature buffer layer and the AlNP high-temperature buffer layer reduces the dislocation density of the superlattice layer and the multi-layer quantum well light emitting layer formed thereon, and reduces the light from the multi-layer quantum well layer in the buffer layer. Suppress absorption. In the present invention, for example, the x can be about 0.05, and the y can be about 0.01.
[0013]
The present invention also relates to a light emitting device using a nitride-based compound semiconductor layer, comprising a substrate and an AlN _1-x As _x low-temperature buffer layer (0 <x <1) formed on the substrate. the _{AlN 1-x P} x low-temperature buffer layer _{AlN 1-y} as y high-temperature buffer layer formed on (where, 0 ≦ y <1) and, formed on the _{AlN 1-y} as y high-temperature buffer layer A first conductivity type GaN-based superlattice layer, a GaN-based multilayer quantum well light emitting layer formed on the first conductivity type GaN-based superlattice layer, and a second conductive layer formed on the GaN-based quantum well light-emitting layer. And a conductive type GaN-based superlattice layer. The combination of the AlNAs low-temperature buffer layer and the AlNAs high-temperature buffer layer reduces the dislocation density of the superlattice layer and the multi-layer quantum well light emitting layer formed thereon, and reduces the light from the multi-layer quantum well layer in the buffer layer. Suppress absorption. In the present invention, for example, the x can be about 0.05, and the y can be about 0.01.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 shows a configuration of an LED according to the present embodiment. A first buffer layer (or low-temperature buffer layer) 12 and a second buffer layer (or high-temperature buffer layer or base layer) 14 are formed on a substrate 10 such as sapphire. On the second buffer layer 14, a strained superlattice layer SLS16 functioning as an n-type cladding layer, a multi-layer quantum well MQW layer 18 functioning as a light emitting layer, and a strained superlattice layer SLS layer 20 functioning as a p-type cladding layer are formed. You. After the electrode formation layer 22 is formed on the SLS layer 20 and the surface is etched until the second buffer layer 14 is exposed, the p-type electrode 24 is formed on the electrode formation layer 22 and the n-type electrode 24 is formed on the second buffer layer 14. A mold electrode 26 is formed.
[0016]
The SLS layer 16 may have a configuration in which, for example, AlGaNs having different compositions are alternately stacked by 50 pitches. As the MQW layer 18, for example, an AlGaN well layer and an AlInGaN barrier layer can be alternately stacked at several pitches. The SLS layer 20 may have a configuration in which AlGaNs having different compositions are alternately stacked by 20 pitches. As the electrode forming layer 22, p + GaN or the like is used.
[0017]
In order to make the SLS layer 22 and the electrode forming layer 24 p-type, Mg may be doped as an acceptor and activated by using electromagnetic energy, heat energy, or a combination of heat energy and electromagnetic energy.
[0018]
In the conventional LED, GaN or AlN is used as the first buffer layer 12 or the second buffer layer 14, but in the present embodiment, AlN _1-x P _x (where 0 < x <1) is used, and AlN _1-y P _y (where 0 ≦ y <1) is used as the second buffer layer 14. The first buffer layer 12 is formed at a low temperature (about 500 ° C.), and the second buffer layer 14 is formed at a high temperature (for example, about 1080 ° C.).
[0019]
The emission intensity when the current was injected while changing the composition of x and y was as follows. The injection current was 20 mA, and the voltage at that time was 3.6 V to 3.8 V.
[0020]
[Table 1]

In the table, “LT” indicates low-temperature formation, and “HT” indicates high-temperature formation. For example, sample A in Table 1 uses AlN _0.95 P _0.05 as the first buffer layer (low temperature buffer layer) 12 and AlN _0.99 P ₀ as the second buffer layer 14 (high temperature buffer layer or underlayer). _This is a sample using _.01 . This is the case where X = 0.05 (composition ratio 5%) and y = 0.01 (composition ratio 1%). Sample B uses the same AlN _0.95 P _0.05 as the first buffer layer (low temperature buffer layer) as sample B, and uses AlN as the second buffer layer 14 (high temperature buffer layer or underlayer). It is. This is the case where y = 0 (composition ratio 0%). The emission intensity is a relative value based on the emission intensity of Sample E. Sample E uses GaN for the first buffer layer 12 and the second buffer layer 14. The emission intensity of each sample is indicated by a plurality (9) of average values. The emission intensity of Sample E is about 1 mW at an injection current of 20 mA.
[0021]
Sample E has a dislocation density of about 5 × 10 ⁸ cm ⁻² , the lowest among all the samples. However, since GaN absorbs light emitted from the MQW layer 18, the light extraction efficiency is low. Comparing Sample A and Sample E, the emission intensity is 5.2 times higher than that of Sample E although the dislocation density of Sample A is higher. This is because AlNP, which is the buffer layer of Sample A, hardly absorbs light from the MQW layer 18. Further, it is considered that the light from the MQW layer 18 is scattered due to the unevenness of the surface of the AlNP. The relative emission intensities of Sample B and Sample C are 4.5 times and 2.5 times, respectively, as compared with Sample E due to lower absorption in the buffer layer, but are lower than Sample A. This is considered to be because the dislocation density of Sample B and Sample C is higher than that of Sample A. Sample D has a lower emission intensity than sample E. It is considered that this is because the dislocation density in the SLS 16 layer and the MQW layer 18 formed on the AlGaN layer as the second buffer layer 14 is high, and there is light absorption in AlGaN.
[0022]
As described above, by using AlN _1-x P _x as the first buffer layer 12 and using AlN _1-y P _y as the second buffer layer, the light emission intensity can be remarkably improved. By using AlNP for both the second buffer layer 12 and the second buffer layer 14, a low dislocation density and low light absorption are realized, and as a result, an LED with high light extraction efficiency can be obtained.
[0023]
Hereinafter, the first buffer layer 12 and the second buffer layer 14 will be described in more detail.
[0024]
FIG. 2 shows the substrate 10, the first buffer layer 12, and the second buffer layer 14. The first buffer layer 12 is AlNP formed at a low temperature, and the second buffer layer is AlNP formed at a high temperature. Specifically, it is formed as follows.
[0025]
First, the sapphire c-plane substrate 10 is placed in an MOCVD apparatus, and heat-treated at 1150 ° C. in a hydrogen atmosphere. Then, AlNP is formed at a temperature of 500 ° C. to form the first buffer layer 12. The thickness of the first buffer layer 12 is about 20 nm. The thickness of the layer and the growth temperature are examples, and the same layer is formed if the thickness of the layer is in the range of 10 to 50 nm and the growth temperature is in the range of 400C to 700C. Thereafter, the temperature is increased to 1080 ° C., and AlNP is formed to form the second buffer layer 14. The thickness of the second buffer layer 14 is about 2 μm. AlNP of the first buffer layer 12 and the second buffer layer 14 is formed by MOCVD using trimethyl aluminum, ammonia, and phosphine as source gases. The flow rate of each source gas is trimethylaluminum 10 to 150 μmol / min, ammonia 15 SLM (Standard Liter per minute: reference flow rate unit), and phosphine 1 to 100 sccm. The pressure in the reactor during growth is 100 Torr. For comparison, GaN or AlN was formed at a low temperature as the first buffer layer 12, and then AlNP was formed as the second buffer layer 14. A sample configuration is shown below.
[0026]
Sample α: substrate / LT-AlNP / HT-AlNP
Sample β: substrate / LT-GaN / HT-AlNP
Sample γ: substrate / LT-AlN / HT-AlNP
In samples α and γ, the surface of HT-AlNP as the second buffer layer 14 is a mirror surface, but the surface of sample β is cloudy.
[0027]
The P composition in AlNP depends on the flow rate of the source gas and the growth temperature. At the same source gas flow rate, the P composition in LT-AlNP is much larger than the P composition in HT-AlNP. For example, when the phosphine flow rate is 50 sccm, the P composition ratio in LT-AlNP is about 10%, the P composition ratio in HT-AlNP is about 1%, and the P composition ratio in HT-AlNP is LT-AlNP. It becomes about 1/10 of the P composition ratio in the inside. When the growth temperature of HT-AlNP is lowered from 1080 ° C. to 1000 ° C., the P composition ratio in HT-AlNP becomes 1.5%. The P composition ratio in AlNP is measured by, for example, SIMS (secondary ion mass spectrometer). When the sample α is represented by the composition ratio, it is substrate / LT-AlN _0.9 P _0.1 / HT-AlN _0.99 P _0.01 , and when the sample γ is represented by the composition ratio, the substrate / LT-AlN / HT-AlN _0.99 P _0.01 . When the dislocation density of these samples α and γ is measured by a plane TEM (transmission electron microscope), the sample α is about 5 × 10 ⁹ cm ⁻² and the sample γ is about 5 × 10 ¹⁰ cm ⁻² . Therefore, it is understood that the sample α is more desirable from the viewpoint of reducing the dislocation density.
[0028]
Next, while maintaining the P composition ratio in HT-AlNP as the second buffer layer 14 at about 1%, the dislocation density was measured by changing the P composition ratio in LT-AlNP as the first buffer layer 12. did.
[0029]
FIG. 3 shows a change in dislocation density with respect to the P composition ratio in LT-AlNP. The dislocation density decreases sharply by adding about 0.5% of P to LT-AlNP, and further decreases as the P composition increases. However, if the P composition is too high, the dislocation density will increase. Although the optimum P composition of LT-AlNP depends on the P composition of HT-AlNP formed thereon, the optimum P composition ratio in this embodiment is about 5%. An example of the optimum composition ratio in the present embodiment is as follows.
[0030]
Substrate 10 / first buffer layer (LT-AlN _0.95 P _0.05 ) 12 / second buffer layer (HT-AlN _0.99 P _0.01 )
The band gap energy of HT-AlN _0.99 P _0.01 is estimated to be about 6 eV at room temperature.
[0031]
FIG. 4 shows another configuration of the substrate 10, the first buffer layer 12, and the second buffer layer 14. HT-AlN or HT-AlGaN is used as the second buffer layer 14, and LT-AlNP or the like is used as the first buffer layer 12. The specific manufacturing method is as follows. The sapphire c-plane substrate 10 is set in an MOCVD apparatus, and heat-treated at 1150 ° C. in a hydrogen atmosphere. Then, AlNP, AlN, and GaN are formed at a temperature of 500 ° C. to form the first buffer layer 12. The thickness of the first buffer layer 12 is about 20 nm. Thereafter, the temperature is increased to 1080 ° C., and AlN is formed to form the second buffer layer 14. The thickness of the second buffer layer 14 is about 2 μm. AlNP is formed by MOCVD using trimethylaluminum, ammonia, and phosphine as source gases. AlGaN is formed using trimethylaluminum, trimethylgallium, and ammonia as source gases.
[0032]
The composition of each sample and the dislocation density measured by TEM are as follows.
[0033]
[Table 2]

In the table, sample a is formed by forming LT-AlN _0.95 P _0.05 as the first buffer layer 12 and forming HT-AlN as the second buffer layer 14. In sample d, LT-AlN _0.95 P _0.05 was formed as the first buffer layer 12 and HT-Al _0.15 Ga _0.85 N was formed as the second buffer layer 14.
[0034]
As can be seen from the table, the dislocation density of samples a and d using the first buffer layer 12 to which P is added is lower by about one digit. Further, the dislocation density of sample a is lower than that of sample d, and the effect of using P as the first buffer layer 12 and using AlN as the second buffer layer 14 is more effective than using AlGaN as the second buffer layer 14. Is high.
[0035]
As described above, by using LT-AlNP as the first buffer layer 12 and using HT-AlNP or HT-AlN as the second buffer layer (or using HT-AlGaN), the absorption of light is reduced while the dislocation density is reduced. A suppressed LED can be obtained.
[0036]
It is also possible to replace part or all of Al of HT-AlNP as the second buffer layer 14 with Ga. When part or all of Al is replaced with Ga, the growth rate increases. One example is substrate / LT-AlN _0.95 P _0.05 / HT-Al _0.5 Ga _0.5 N _0.99 P _0.01 . The growth temperature of HT-AlGaNP is 980 ° C. The growth temperature of HT-AlGaNP is lower than that of AlNP. This is considered to be because the Ga—P bond is weaker than the Al—P bond. Also, the dislocation density tends to increase slightly with increasing Ga. Therefore, it is preferable to replace a part of Al with Ga by an appropriate amount. FIG. 5 shows the configuration of the substrate 10, the first buffer layer 12, and the second buffer layer 14 in this case.
[0037]
Further, HT-AlInNP in which part of Al of HT-AlNP is replaced by In may be considered, but in this case, the growth temperature needs to be 850 ° C. or lower to take In into the solid phase, and the growth rate decreases. I do. In addition, the surface roughness becomes remarkable.
[0038]
In the present embodiment, As may be added instead of adding P. For example, LT-AlNAs are formed as the first buffer layer 12 on the substrate 10, and AlN is formed as the second buffer layer 14. The SLS layer 16, the MQW layer 18, and the SLS layer 20 shown in FIG. 1 were formed on the second buffer layer 14, and the p-type electrode 24 and the n-type electrode 26 were further formed. A strength of 4.0 was obtained. Although the light output is weaker than the case where P atoms are used, As atoms can produce the same effect as P atoms.
[0039]
A configuration example using As atoms instead of P atoms is shown below.
[0040]
Substrate / LT-AlNAs / HT-AlNAs
Substrate / LT-AlNAs / HT-AlN
Substrate / LT-AlNAs / HT-AlGaN
Substrate / LT-AlNAs / HT-AlGaNAs
The composition ratio is, for example, substrate / LT-AlN _0.95 As _0.05 / HT-AlN _0.99 As _0.01 . FIG. 6 shows a configuration example in this case.
[0041]
In the present embodiment, it is also possible to use LT-AlNP as the first buffer layer 12 and use HT-AlNAs as the second buffer layer 14. It is also possible to use LT-AlNAs as the first buffer layer 12 and HT-AlNP as the second buffer layer 14.
[0042]
Further, in the present embodiment, the LED in which the SLS layer and the light emitting layer are stacked on the first buffer layer 12 and the second buffer layer 14 has been described, but the present invention can be applied to electronic devices other than the LED. . One example is an electronic device such as a FET using GaN as an electrically conductive layer. By growing an AlNP crystal or AlNAs crystal on a substrate to form an underlayer, and forming an FET or the like using GaN as an electrically conductive layer on the underlayer, an electronic device with reduced dislocation density can be obtained. The basic configuration is substrate / AlNP (or AlNAs) / semiconductor layer, and the materials of the substrate and the semiconductor layer are arbitrary. By reducing the dislocation density of the semiconductor layer, improvement in electric characteristics of the semiconductor layer can be expected. The first buffer layer and the second buffer layer are integrated to form an AlNP (AlNAs) layer.
[0043]
【The invention's effect】
As described above, according to the present invention, the dislocation density can be suppressed. Further, when applied to a light emitting device such as an LED, it is possible to suppress dislocation density and light absorption.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an LED according to an embodiment.
FIG. 2 is a configuration diagram of a first buffer layer and a second buffer layer.
FIG. 3 is a graph showing a relationship between a P composition ratio in LT-AlNP and a dislocation density in HT-AlNP.
FIG. 4 is another configuration diagram of a first buffer layer and a second buffer layer.
FIG. 5 is a diagram showing still another configuration of the first buffer layer and the second buffer layer.
FIG. 6 is a diagram showing still another configuration of the first buffer layer and the second buffer layer.
[Explanation of symbols]
Reference Signs List 10 substrate, 12 first buffer layer, 14 second buffer layer, 16 SLS layer, 18 MQW layer, 20 SLS layer, 22 electrode forming layer, 24 p electrode, 26 n electrode.

Claims (11)

A nitride-based compound semiconductor device comprising: a first buffer layer and a second buffer layer formed on a substrate; and a nitride-based compound semiconductor layer formed on the second buffer layer.
Wherein the first buffer _{layer, AlN 1-x P} x (where, 0 <x <1) nitride-based compound semiconductor device which is a. The device of claim 1,
The nitride-based compound semiconductor device, wherein the second buffer layer _satisfies AlN _{1-y Py} (where 0 ≦ y <1). A nitride-based compound semiconductor device comprising: a first buffer layer and a second buffer layer formed on a substrate; and a nitride-based compound semiconductor layer formed on the second buffer layer.
The nitride-based compound semiconductor device, wherein the first buffer layer is AlN _1-x As _x (where 0 <x <1). The device according to claim 3,
The second buffer _{layer, AlN 1-y} As y (where, 0 ≦ y <1) nitride-based compound semiconductor device which is a. The device according to any one of claims 1 and 3,
The said 2nd buffer layer is AlGaN, The nitride compound semiconductor device characterized by the above-mentioned. The device of claim 1,
The nitride-based compound semiconductor device, wherein the second buffer layer is made of AlGaNP. The device according to claim 3,
The nitride-based compound semiconductor device, wherein the second buffer layer is made of AlGaNAs. The apparatus according to any one of claims 1 to 7,
The nitride-based compound semiconductor layer formed on the second buffer layer,
an n-type GaN-based layer;
a p-type GaN-based layer;
A GaN-based light-emitting layer formed between the n-type GaN-based layer and the p-type GaN-based layer;
A nitride-based compound semiconductor device. A light emitting device using a nitride-based compound semiconductor layer,
Board and
An AlN _1-x P _x low temperature buffer layer (0 <x <1) formed on the substrate;
An AlN _1-y P _y high temperature buffer layer (0 ≦ y <1) formed on the AlN _1-x P _x low temperature buffer layer;
A first conductivity type GaN-based superlattice layer formed on the AlN _{1-y Py} high temperature buffer layer;
A GaN-based multilayer quantum well light emitting layer formed on the first conductivity type GaN-based superlattice layer;
A second conductivity type GaN-based superlattice layer formed on the GaN-based multilayer quantum well light emitting layer;
A light emitting device comprising: A light emitting device using a nitride-based compound semiconductor layer,
Board and
An AlN _1-x As _x low-temperature buffer layer (0 <x <1) formed on the substrate;
The _{AlN 1-x P} x low-temperature buffer layer _{AlN 1-y} As y high-temperature buffer layer formed on a (where, 0 ≦ y <1),
A first conductivity type GaN-based superlattice layer formed on the _{AlN 1-y} As _y high-temperature buffer layer,
A GaN-based multilayer quantum well light emitting layer formed on the first conductivity type GaN-based superlattice layer;
A second conductivity type GaN-based superlattice layer formed on the GaN-based multilayer quantum well light emitting layer;
A light emitting device comprising: The device according to any one of claims 9 and 10,
The light emitting device according to claim 1, wherein x is about 0.05 and y is about 0.01.

Images