JP5093740B2 - Semiconductor crystal film growth method - Google Patents

Semiconductor crystal film growth method Download PDF

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JP5093740B2
JP5093740B2 JP2001225534A JP2001225534A JP5093740B2 JP 5093740 B2 JP5093740 B2 JP 5093740B2 JP 2001225534 A JP2001225534 A JP 2001225534A JP 2001225534 A JP2001225534 A JP 2001225534A JP 5093740 B2 JP5093740 B2 JP 5093740B2
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JP2003037288A (en
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明伯 纐纈
紀仁 河口
みゆき 正木
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IHI Corp
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IHI Corp
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【0001】
【発明の属する技術分野】
本発明は、基板上に半導体結晶膜を成長させる半導体結晶膜の成長方法に関する。
【0002】
【従来の技術】
図4は、非対称ダブルヘテロ構造のpn接合型青色LEDの断面構造図である。この図に示すように、サファイア基板の表面にAlNバッファ層を介してGaN層を成長させ、さらにその上にInGaNの半導体被膜を成長させることにより青(B)を発光する青色LEDを形成することができる。また、この図において、InGaN中のInNの成分比率を変えることにより、赤(R)、緑(G)、青(B)の3原色を発光させることができ、そのうち緑(G)、青(B)の2原色のLEDは既に実現している。
すなわち、一般にInGaNはGaNとのダブルヘテロ構造あるいはInGaN/GaNのマルチ量子井戸構造によりレーザや発光ダイオード素子が作製される。
【0003】
図5は、主な半導体のバンドギャップと格子定数の関係図である。この図において、バンドギャップ(eV)と波長(μm)が対応しており、赤(R)、緑(G)、青(B)の順で波長が短くなり、かつInGaN中のInNの成分比率が低くなる。すなわち、既に実現している緑(G)、青(B)の2原色のLEDに比較して、約650μmの波長の赤(R)を発光する赤色LEDでは、InGaN中のInNのモル分率を約0.7以上に高める必要がある。
【0004】
図6は、InGaN中のInNのモル分率yと平衡温度との関係図である。この図に示すように、約650μmの波長の赤(R)を発光する赤色LEDを形成するために、InGaN中のInNのモル分率yを約0.7以上に高めると、その平衡温度は約500℃以下となる。そのため、GaN層の表面にInGaNの半導体被膜を成長させる過程で、GaN層や形成されたInGaNを約500℃以上に加熱すると、InGaNが熱分解してしまう問題点があった。
なお、図6は原料分圧が低い真空中で加熱した場合の関係であり、気相成長の場合にはこの図に従わない。例えば、日亜化学では約750℃から約800℃でInが0.2程度のInGaNを成長している。
【0005】
サファイア基板の表面にInGaNの半導体被膜を成長させる手段として、「半導体結晶膜の成長方法」が開示されている(特開平04−164895号)。この方法は、図7に模式的に示す装置を用い、MOVPE法(有機金属化合物気相成長法)で基板1の上面に半導体被膜を成長させるものである。すなわち、この方法は、サファイア基板1をサセプター4の上に載せ、反応容器6内をH2で置換し、基板1の温度を約550℃に保持し、副噴射管3から水素と窒素を、反応ガス噴射管2からアンモニアガスと水素とTMG(トリメチルガリウム)ガスとTMI(トリメチルインジウム)ガスを供給して、サファイア基板1の表面にInGaNの半導体被膜を成長させるものである。なお、この図において、5はシャフト、7はヒータ、8は排気口、9は放射温度計である。また、MOVPE(有機金属化合物気相成長法)の代わりに、MOMBE法(有機金属分子ビームエピタキシー法)を適用することもできる。
【0006】
この方法により、Ga0.94In0.06Nの半導体被膜を2インチ基板全面にわたって、膜厚2μmで均一に成長させることに成功している。しかし、この方法では、成長させたInGaN中のInNのモル分率yが低く(0.06)、赤(R)を発光する赤色LEDを形成することができない欠点があった。すなわち、この例では窒素の前駆体としてアンモニアを用いているが、アンモニアはN−Hの結合エネルギーが大きいため、基板上で反応させるためには、基板温度をできるだけ上げる必要がある。ところが、赤を発光させるInGaNは、InNの組成が高く、上述したように、InNのモル分率yが高くなると、分解温度が約500℃程度まで下がっているため、この方法では、基板温度が高すぎ、赤発光のInGaNは成長させることができなかった。
しかし、例えば、日亜化学、その他では0.2〜0.3のIn組成のInGaNが成長している。
【0007】
図8は、低温堆積層を用いたGaNのMOVPE(有機金属化合物気相成長法)の基板温度プログラムの概略図である。この図に示すように、従来、サファイヤ基板上にAlN(又はGaN)のバッファ層は約500℃で形成され、次いでGaNが約1100℃で形成されている。更にその上のInGaN層は、上述した例では約750℃で成長させている。
【0008】
図9は、アンモニアがIII族原料に対して供給過剰で成長が行われていると仮定したときの、2元化合物InN,GaM,AlNの成長速度の基板温度依存性の概略を示す。成長速度一定の温度領域があり、それより高温でも低温でも成長速度は減少する。低温で成長速度が減少するのは、原料ガスの分解効率が低下するためである。また、高温で成長速度が減少するのは、昇華が多くなるためである。高温では、水素のエッチング反応も顕著になるので、成長速度の低下はより低い温度で生じる。
【0009】
【発明が解決しようとする課題】
上述したように、従来、pn接合型のLEDは、サファイヤ基板上にバッファ層を介して約1000℃でGaN層を成長させ、次いで、その上にInGaN層を約750℃で成長させていた。しかし、この方法によるLED構造は、InGaN層の結晶成長速度が遅く、格子欠陥が発生しやすく、その品質が低い問題点があった。
【0010】
本発明はかかる問題点を解決するために創案されたものである。すなわち、本発明の目的は、従来と同様のpn接合型のLEDにおいて、その結晶構造を改善し、成長速度を高め、格子欠陥を低減してその品質を高めることができる半導体結晶膜の成長方法を提供することにある。
【0011】
【課題を解決するための手段】
上記問題点を解決するために、本発明の発明者等は、ウルツ鉱型構造のGaNの格子極性に着目し、その分解速度と成長速度に及ぼす温度の影響を鋭意研究した。その結果、従来の約1000℃におけるGaN層の成長極性は、(0001)面(Ga極)が支配的であり、その上のInGaN層の成長も、極性が同じ(0001)面となる。一方、約820℃以下の低温における成長では、この(0001)面の成長は、逆の(000−1)面(N極)の成長に比べ成長速度が遅く、分解速度が速くなるため、格子欠陥が発生しやすく、その品質が低下するものとの知見を得た。本発明はかかる新規の知見に基ずくものである。
【0012】
すなわち、本発明によれば、サファイヤ基板上にバッファ層を介してGaN層を成長させ、次いで、その上にInGaN層又はInN層を成長させる半導体結晶膜の成長方法において、
前記基板の結晶上にバッファ層を成長させ、該バッファ層上に面方位が(000−1)面であるGaN層の成長を780℃以下,500℃以上で行い、次いで面方位が(000−1)面であるInGaN層又はInN層の成長を800℃以下で行う、ことを特徴とする半導体結晶膜の成長方法が提供される。
【0013】
本発明の方法によれば、GaN層を従来より低温の約820℃以下、約500℃以上で行うので、この温度領域では、GaN層の成長極性は、(000−1)面(N極)が支配的となる。次いで、GaN層の上のInGaN層又はInN層は、約800℃以下で行うため、InNのモル分率yを高め(例えば約0.7以上)、InGaNの熱分解を防止することができる。
また、このInGaN層又はInN層は、その下地となるGaN層が(000−1)面に成長しているので、InGaN層又はInN層の成長極性も、下地層と同じ(000−1)面となる。
【0014】
更に、約800℃以下,約400℃以上の低温領域では、InGaN層又はInN層の(000−1)面の成長は、上述の研究の結果から、従来の(0001)面の成長に比べ成長速度が速く、分解速度が遅く、さらに、エネルギー的に安定な成長方向であることから結晶原子配置のズレが起こりにくいことから、高品質のInGaN層又はInN層が得られることが確認された。従って、成長極性が(000−1)面となるInGaN層又はInN層は、(0001)面の成長の場合に比較して、格子欠陥が低減されるため、その品質は従来より優れたものとなる。
【0015】
本発明の好ましい実施形態によれば、前記各層の成長は、MOVPE(有機金属化合物気相成長法)、HVPE(ハイドライド気相成長法)又はMOMBE法(有機金属分子ビームエピタキシー法)による。
これらの成長法により、基板温度を所定の温度に設定しながら、効率よく各層を成長させることができる。
【0016】
また、前記Gaの前駆体はGaCl、Ga(CH33又はGa(C253であり、Inの前駆体はIn(CH33又はIn(C253であり、Nの前駆体はアンモニア、MNH2(メチルアミン)、DMNH(ジメチルアミン)、TMN(トリメチルアミン)、N22(ヒドラジン)、(CH3)NH-NH2(モノメチルヒドラジン)、又は(CH32N-NH2(ジメチルヒドラジン)である。
これらの前駆体を励起・分解することにより、GaN層、InGaN層およびInN層の成長を効率よく行うことができる。
【0017】
【発明の実施の形態】
以下、本発明の好ましい実施形態を図面を参照して説明する。なお、各図において共通する部分には同一の符号を付し、重複した説明を省略する。
【0018】
図1は、ウルツ鉱型結晶構造(A)と四面体クラスタ(B)の模式図である。GaN、InGaNおよびInN等のIII族窒化物結晶は通常、ウルツ鉱型結晶構造かジンクブレンド型構造となるが、ここではウルツ鉱型結晶構造の場合を説明する。
ウルツ鉱型結晶構造は、対称中心をもたず、(0001)面(Ga極)と(000−1)面(N極)を持つ。図1から明らかなように、III族原子(Ga,In等)とV族原子(N)とを入れ替えた構造は、元の結晶の向きを反転させたものである。この2種類の方向では最外表面に出ている原子種やまわりの原子との結合配置が異なり、従って表面再構成構造が違ってくる。
III族窒化物結晶では、どちらの極性の向きに成長するかは、基板の種類、その他の成長条件に依存する。極性によって表面構造が異なるので結晶成長過程にも差が出てくる。その結果、得られるエピタキシャル層の微細組織や成長面形状にも大きな差が現れる。
【0019】
図2は、後述する実施例で得られたGaN層の分解速度と温度の関係図である。この図において、横軸は温度(上軸)とその逆数(下軸)、縦軸はGaN層の分解速度、図中の●は(0001)面(Ga極)、○は(000−1)面(N極)である。
この図から、約820℃において、(0001)面と(000−1)面の分解速度が逆転しており、高温側では(000−1)面の分解速度が大きく、低温側では(0001)面の分解速度が大きいことがわかる。なお、図中の縦軸は対数表示(指数関数表示)であるため、実際の差は、2倍以上あることに留意する必要がある。
【0020】
図3は、同様に後述する実施例で得られたGaN層の成長速度と温度の関係図である。この図において、横軸は温度、縦軸はGaN層の成長速度、図中の●は(0001)面(Ga極)、○は(000−1)面(N極)である。
この図から、成長速度も約820℃において、(0001)面と(000−1)面が逆転しており、高温側では(0001)面の成長速度が大きく、低温側では(000−1)面の成長速度が大きいことがわかる。
【0021】
図2と図3から、約820℃を境にして、それより低い約750℃までの温度範囲において、(0001)面の成長速度が低く、かつその分解速度が大きいことがわかる。すなわち、この温度領域では、Ga極のエッチングが激しく行われており、一方で成長速度も遅いため、結果として品質の劣るGaN層が成長するものと考えられる。
なお、InNおよびInGaNの成長においても、InNおよびInGaNがGaNと同じ結晶構造を持つIII-V族化合物半導体であることから、GaNの成長と同様に約820℃付近に安定な表面の境があると類推される。しかし、InGaNおよびInNの場合は約820℃以上の高温では分解蒸気圧が高く、通常のMOVPE、MOMBEの成長条件では成長ができない。従って、本来のInGaNおよびInNの安定な成長方向は(000−1)方向であり、現在、通常行われているInGaNおよびInNの成長方向(0001)は安定な成長方向とはいえない。
【0022】
上述した新規の知見に基ずき、本発明の方法では、図4に示したサファイヤ基板上にバッファ層を介してGaN層を成長させる温度を、従来の約1000℃から大幅に低温化して、その成長を約800℃以下で行う。この結果、図2と図3から、この温度領域では、GaN層の成長極性は(000−1)面が支配的となる。
また、本発明では、その上のInGaN層の成長は、約500℃以下,約400℃以上で行う。これにより、InGaN層の成長極性も同じ(000−1)面となる。
【0023】
すなわち、GaN層を従来より低温の約820℃以下、約500℃以上で行い、GaN層を(000−1)面に成長させ、次いで、GaN層の上のInGaN層又はInN層は、約800℃以下で行う。これにより、InGaN層又はInN層の成長の際に、その下地となるGaN層が(000−1)面に形成されているので、InGaN層又はInN層の成長極性は、下地層と同じ(000−1)面となる。
また、約800℃以下の温度範囲では、(000−1)面の成長は、従来の(0001)面の成長に比べ成長速度が速く、分解速度が遅いため、その品質は従来より優れたものとなる。
【0024】
本発明の方法において、各層の成長は、HVPE(ハイドライド気相成長法)、MOVPE(有機金属化合物気相成長法)、又はMOMBE(有機金属分子ビームエピキタシー法)による。
すなわち、例えば、サファイア基板を反応容器内で温度調節手段(例えばヒータ)により調節し、GaN層の成長を約820℃以下、約500℃以上で行う。また、InGaN層およびInN層は、InGaNが熱分解しない温度(例えば約800℃以下)で行う。
【0025】
また、反応容器内にIn,Ga,Nの前駆体をガス導入部より順次又は同時に供給する。Gaの前駆体はGaClであり、Nの前駆体はアンモニア、MNH2(メチルアミン)、DMNH(ジメチルアミン)、TMN(トリメチルアミン)、N22(ヒドラジン)、(CH3)NH-NH2(モノメチルヒドラジン)、又は(CH32N-NH2(ジメチルヒドラジン)であるのがよい。
【0026】
【実施例】
以下、本発明の実施例を説明する。
ウルツ鉱型構造のGaNは、そのc軸方向に沿った極性、すなわち(0001)面(Ga極)と(000−1)面(N極)を有する。それゆえ、クリーニング又はエッチング面に対するGaNの分解メカニズムを研究することは非常に重要である。この実施例では、その場重力測定モニター法(GM法)を用いてサファイア基板(0001)面上のGaN単結晶の面極性に対する分解速度を試験した。
【0027】
試験装置は、縦型反応管と微少重量記録装置とからなる。この微少重量記録装置は、0.004μg(2.0cm2の面積のGaNの3.3×10-6μmにほぼ相当する)の感度を有する。キャリアガスはH2とイナートガスを用い、イナートガスとしてHeを用いた。キャリアガス中の水素分圧(PH2)はH2+Heに対するH2の比率の変化により変化する。鏡面仕上げしたGaN基板(0001)の片面を1000Å厚のSiO2層で覆い、シリカ繊維でマイクロバランスから吊り下げた。これにより、GaN基板(0001)表面の極性依存性を計測することができる。
【0028】
図2は、この試験で得られたGaN層の分解速度と温度の関係図である。
この図から明らかなように、H2キャリアガス環境(PH2=1)における分解速度は、650℃から950℃の温度範囲において、面極性にかかわらず、温度の上昇により指数関数的に増加する。また、分解速度自体は格子極性に依存して相違することが明らかになった。820℃以下の低温範囲において、GaNの(0001)面の分解速度は(000−1)面よりも速い。反対に、850℃から950℃までの高温領域では、GaNの(000−1)面の分解速度が(0001)面より速い。この結果の理由は、GaNの(0001)面と(000−1)面の分解プロセスにおける活性化エネルギーの相違による。
【0029】
更に、GaN面(0001)および(000−1)面の分解速度と水素分圧の関係を600℃から950℃まで調べた。その結果、850℃以下の低温領域ではGaNの分解速度は面極性に関係なく水素分圧の3/2乗に比例することが明らかになった。一方、850℃以上の高温領域では、やはり、分解速度は両極性に関係なく水素分圧の1/2乗に比例することが明らかになった。このことは、低温領域と高温領域で分解速度を制御する律速反応が異なることを意味している。一方、GaN(s)とH2(g)との反応の熱力学解析から、この反応で生じる主な気相分子種はNH3およびGaHであることが明らかになっており、低温領域と高温領域の水素との反応による律速反応は各々式(1)および式(2)で示されることが明らかである。
GaN(表面)+3/2H2(g)→Ga(表面)+NH3(g)・・・(1)(低温領域)
GaN(表面)+1/2H2(g)→N(表面)+GaH(g)・・・(2)(高温領域)
【0030】
一方、GaNの成長時においてもキャリヤガスとして水素ガスが用いられていること、さらにGaNの成長反応により水素が生成されることから、GaN表面と水素との反応が同時に起こっていると考える必要がある。さらに、実際に得られる成長速度は析出反応と分解反応との差と考えられる。このことは図3の成長と温度の関係からも明らかである。
【0031】
上記の結果から、分解および成長において、低温領域ではGaN(000−1)面が支配的になり、高温領域ではGaN(0001)面が支配的になることが明らかである。
【0032】
このような発明により、下記のような事実が明らかになるとともに、InGaNおよびInNの高品質結晶が得られる成長条件が明らかになった。
【0033】
事実1:サファイヤなどの無極性の基板結晶を用いた成長では、特に、成長温度によりサファイヤ上に成長するGaNの成長面方位が決定される。温度と成長面方位の関係は、低温領域では(000−1)面、高温領域では(0001)面である。一般にGaNは1000℃付近の高温領域が用いられており、(0001)面成長が支配的になることが予想され、事実、(0001)Ga終端面が成長面であることが明らかにされている。
【0034】
事実2:GaAs(111)結晶を基板結晶に用いた場合、GaAs(111)A面はGaN(0001)面と、GaAs(111)B面は(Gan(000−1)面とIII族およびV族およびV族原子の結合状態が等価である。このために、GaAs(111)A面を用いた場合、約500℃でのバッファー層成長後の1000℃以上の成長により良好なGaN成長が可能であるとともに、表面が(0001)面である事実と一致する。一方、GaAs(111)B面を用いて、約500℃でのバッファー層成長後の850℃以上の成長においては、良好なGaN成長が得られなく、さらに、1ミクロン以上の成長表面は(0001)となっており、成長の初期に成長方向が反転していることが明らかである。
【0035】
(注1)GaAs(111)A面上の成長は、Y.Kumagai et al. Jpn.J.Appl.Phys.,39(2000)L149およびY.Kumagai et al. Jpn.J.Appl.Phys.,39(2000)L703.から明らかです。
【0036】
(注2)成長面の測定については、我々のサンプルを用いた、下記の発表から明らかです。2001年春季 応用物理学関係連合講演会29a-L-2 小川他(名古屋大学工学部秋本先生のグループ)
(内容:GaAs(111)AおよびGaAs(111)B面上へのGaN成長において、100nm以下のGaNバッファー層の表面は各々(0001)および(000−1)面であるが、その上に920から1000℃でGaNを1ミクロン以上成長後の表面はどちらも(0001)面であった。)
【0037】
事実3:図3に示した単結晶GaN基板を用いた成長実験により得られた表面はGaN(0001)面およびGaN(000−1)面上には各々GaN(0001)面およびGaN(000−1)面が成長膜厚に関係なく得られた。
【0038】
事実4:従来InGaNおよびInNはサファイヤ基板結晶上に約500℃でバッファー層を成長後、約1000℃程度で成長させたGaN結晶上に、800℃以下の低温領域で成長がされている。このために、(0001)成長面上に(000−1)成長面が安定なInGaNあるいはInNを(0001)成長面で成長することになり、原子配置の不安定性にともなう欠陥やその欠陥に誘発された組成分離が起こる。このため、高品質の結晶成長が難しく、特にIn組成が大きなInGaNあるいはInNは光学特性が得られる結晶が得られていない。
【0039】
事実5:レーザ素子などを目的にしたInGaNあるいはInNの成長において、高圧法や昇華法により作成したGaN単結晶基板あるいはサファイヤ基板又はGaAs基板などを用いた厚膜成長で製造したGaN単結晶基板が用いられている。この場合も、初期にGaNやAINの成長が約1000℃付近で成長させられるために、GaN(0001)面が成長面に用いられており、上記の事実4と同様な現象が出ている。
【0040】
実施例1:
(1)サファイヤ基板を用いたMOVPE成長で、バッファー層を約500℃で成長後、1000℃で約2ミクロンのGaNを成長後、780℃で0.5ミクロンのIn0.2Ga0.8Nの成長を行った。一方、(2)同様にサファイヤ基板を用いてMOVPE成長で、バッファー層を約500℃で成長後、800℃で約2ミクロンのGaNを成長後、780℃で0.5ミクロンのIn0.2Ga0.8Nの成長を行った。成長表面の面分析により、(1)で得られた表面は(0001)面で、(2)は(000−1)面であった。室温でのPL(フォトルミネッセンス)測定の結果、高温GaN成長の試料の半値幅が165meVであったのに対して、低温GaN成長の試料では77meVと半減し結晶品質が向上した。
【0041】
実施例2:
GaAs(111)B面を基板結晶に用いて、MOVPE成長によりバッファー層を約500℃で成長後、780℃でGaNを1.5ミクロン成長し、その上に、780℃で0.6ミクロンのIn0.3Ga0.7Nの成長をした。成長表面は(000−1)面であることを確認した。また、成長したInGaN混晶中には、(0001)成長面の場合に良くみられるIn組成が大きなクラスターも見られず均一な混晶が得られることが明らかになった。
【0042】
実施例3:
GaAs(111)B面を基板結晶に用いて、MOVPE成長によりバッファー層を約500℃で成長後、780℃でGaNを1.5ミクロン成長し、その上に、650℃で0.2ミクロンのIn0.6Ga0.4Nの成長をした。成長表面は(000−1)面であることが確認された。また、成長したInGaN混晶は相分離も見られず、均一な混晶が得られることが明らかになった。X線回折の結果、約2.1minの半値幅のIN0.6Ga0.4Nが得られたことが分かった。一方、サファイヤ基板またはGaAs(111)A面基板を用いてMOVPE成長で約500℃でバッファー層を成長後、約950℃でGaNを成長後、650℃でIn0.6Ga0.4Nの成長を試みたが、相分離を起こし均一なInGaN混晶が得られなかった。
【0043】
実施例4:
GaN単結晶基板(000−1)面を基板に用いて、750℃でGaNを2ミクロン成長後、In0.2Ga0.8N混晶を0.15ミクロン成長した。InGaN混晶中の組成の不安定性もなく均一な組成が得られている。一方GaN(0001)面を基盤にした成長では、混晶中にIn組成が大きなクラスターの存在が明らかになった。また、フォトルミネッセンス測定によりGaN(000−1)面成長の半値幅が小さく品質が良いことが分かった。
【0044】
実施例5:
GaN(000−1)面を基板結晶に用いて、MOVPE成長により780℃でGaNを1.5ミクロン成長し、その上に、650℃で0.2ミクロンのInGaNの成長をした。成長表面(000−1)面であることが確認された。また、成長したInGaN混晶は相分離も見られず、均一な混晶が得られることが明らかになった。X線回折およびフォトルミネッセンスから確認した。
【0045】
上述した本発明の方法によれば、GaN層を従来より低温の約820℃以下、約500℃以上で行うので、この温度領域では、GaN層の成長極性は、(000−1)面(N極)が支配的となる。次いで、GaN層の上のInGaN層又はInN層は、約800℃以下で行うため、InNのモル分率yを高め(例えば約0.7以上)、InGaNの熱分解を防止することができる。
また、このInGaN層又はInN層は、その下地となるGaN層が(000−1)面に成長しているので、InGaN層又はInN層の成長極性も、下地層と同じ(000−1)面となる。
更に、約800℃以下,約400℃以上の低温領域では、InGaN層又はInN層の(000−1)面の成長は、上述の研究の結果から、従来の(0001)面の成長に比べ成長速度が速く、分解速度が遅いことが確認された。従って、成長極性が(000−1)面となるInGaN層又はInN層は、(0001)面の成長の場合に比較して、格子欠陥が低減されるため、その品質は従来より優れたものとなる。
【0046】
なお、本発明は上述した実施例および実施形態に限定されず、本発明の要旨を逸脱しない範囲で種々変更できることは勿論である。
【0047】
【発明の効果】
上述したように、本発明の半導体結晶膜の成長方法は、従来と同様のpn接合型のLEDにおいて、その結晶構造を改善し、成長速度を高め、格子欠陥を低減してその品質を高めることができる等の優れた効果を有する。
【図面の簡単な説明】
【図1】ウルツ鉱型結晶構造(A)と四面体クラスタ(B)の模式図である。
【図2】GaN層の分解速度と温度の関係図である。
【図3】GaN層の成長速度と温度の関係図である。
【図4】InGaNを用いた青色LEDの断面構造図である。
【図5】主な半導体のバンドギャップと格子定数の関係図である。
【図6】InGaN中のInNのモル分率yと平衡温度との関係図である。
【図7】従来の半導体結晶膜の成長方法の模式図である。
【図8】低温堆積層を用いたGaNのMOVPE(有機金属化合物気相成長法)の基板温度プログラムの概略図である。
【図9】2元化合物InN,GaM,AlNの成長速度の基板温度依存性の概略図である。
【符号の説明】
1 サファイア基板、2 反応ガス噴射管、3 副噴射管、
4 サセプター、5 シャフト、6 反応容器、7 ヒータ、
8 排気口、9 放射温度計
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor crystal film growth method for growing a semiconductor crystal film on a substrate.
[0002]
[Prior art]
FIG. 4 is a cross-sectional structure diagram of a pn junction blue LED having an asymmetric double hetero structure. As shown in this figure, a blue LED that emits blue (B) is formed by growing a GaN layer on the surface of a sapphire substrate via an AlN buffer layer and further growing an InGaN semiconductor film thereon. Can do. In this figure, by changing the component ratio of InN in InGaN, three primary colors of red (R), green (G), and blue (B) can be emitted, of which green (G), blue ( The two primary color LEDs B) have already been realized.
That is, in general, InGaN has a double hetero structure with GaN or a multi-quantum well structure of InGaN / GaN to produce a laser or a light emitting diode element.
[0003]
FIG. 5 is a diagram showing the relationship between the band gap and the lattice constant of main semiconductors. In this figure, the band gap (eV) corresponds to the wavelength (μm), the wavelength decreases in the order of red (R), green (G), and blue (B), and the component ratio of InN in InGaN. Becomes lower. That is, in the case of a red LED that emits red (R) having a wavelength of about 650 μm, compared with the green (G) and blue (B) LEDs that have already been realized, the mole fraction of InN in InGaN. Needs to be increased to about 0.7 or more.
[0004]
FIG. 6 is a graph showing the relationship between the molar fraction y of InN in InGaN and the equilibrium temperature. As shown in this figure, when the molar fraction y of InN in InGaN is increased to about 0.7 or more to form a red LED emitting red (R) having a wavelength of about 650 μm, the equilibrium temperature is It becomes about 500 ° C. or less. Therefore, in the process of growing an InGaN semiconductor film on the surface of the GaN layer, if the GaN layer or the formed InGaN is heated to about 500 ° C. or more, the InGaN is thermally decomposed.
FIG. 6 shows the relationship when heated in a vacuum with a low raw material partial pressure, and this figure is not followed in the case of vapor phase growth. For example, Nichia grows InGaN with about 0.2 In at about 750 ° C. to about 800 ° C.
[0005]
As a means for growing an InGaN semiconductor film on the surface of a sapphire substrate, a “semiconductor crystal film growth method” is disclosed (Japanese Patent Laid-Open No. 04-164895). In this method, a semiconductor film is grown on the upper surface of the substrate 1 by the MOVPE method (organometallic compound vapor phase growth method) using the apparatus schematically shown in FIG. That is, in this method, the sapphire substrate 1 is placed on the susceptor 4 and the reaction vessel 6 is placed in the H 2 And the temperature of the substrate 1 is maintained at about 550 ° C., hydrogen and nitrogen are supplied from the sub-injection pipe 3, and ammonia gas, hydrogen, TMG (trimethylgallium) gas and TMI (trimethylindium) gas are supplied from the reaction gas injection pipe 2. And an InGaN semiconductor film is grown on the surface of the sapphire substrate 1. In this figure, 5 is a shaft, 7 is a heater, 8 is an exhaust port, and 9 is a radiation thermometer. Further, instead of MOVPE (organometallic compound vapor phase epitaxy), MOVBE (organometallic molecular beam epitaxy) can be applied.
[0006]
By this method, Ga 0.94 In 0.06 The semiconductor film of N has been successfully grown uniformly over the entire surface of the 2-inch substrate with a film thickness of 2 μm. However, this method has a drawback that a red LED that emits red (R) cannot be formed because the mole fraction y of InN in the grown InGaN is low (0.06). That is, in this example, ammonia is used as a nitrogen precursor. However, since ammonia has a large N—H bond energy, it is necessary to raise the substrate temperature as much as possible in order to react on the substrate. However, InGaN, which emits red light, has a high InN composition. As described above, when the molar fraction y of InN increases, the decomposition temperature decreases to about 500 ° C. Too high and red-emitting InGaN could not be grown.
However, for example, Nichia and others have grown InGaN with an In composition of 0.2 to 0.3.
[0007]
FIG. 8 is a schematic diagram of a substrate temperature program of MOVPE (organometallic compound vapor phase epitaxy) of GaN using a low temperature deposition layer. As shown in this figure, conventionally, a buffer layer of AlN (or GaN) is formed on a sapphire substrate at about 500 ° C., and then GaN is formed at about 1100 ° C. Furthermore, the InGaN layer above it is grown at about 750 ° C. in the example described above.
[0008]
FIG. 9 shows an outline of the substrate temperature dependence of the growth rate of the binary compounds InN, GaM, and AlN when it is assumed that the growth is performed by supplying excess ammonia to the Group III raw material. There is a temperature range where the growth rate is constant, and the growth rate decreases at higher and lower temperatures. The reason why the growth rate decreases at a low temperature is that the decomposition efficiency of the raw material gas decreases. The reason why the growth rate decreases at high temperature is that sublimation increases. At higher temperatures, the hydrogen etching reaction becomes more prominent, so a decrease in growth rate occurs at a lower temperature.
[0009]
[Problems to be solved by the invention]
As described above, conventionally, in a pn junction type LED, a GaN layer is grown on a sapphire substrate through a buffer layer at about 1000 ° C., and then an InGaN layer is grown on the GaN layer at about 750 ° C. However, the LED structure by this method has a problem that the crystal growth rate of the InGaN layer is slow, lattice defects are easily generated, and the quality is low.
[0010]
The present invention has been made to solve such problems. That is, an object of the present invention is to provide a semiconductor crystal film growth method capable of improving the crystal structure, increasing the growth rate, reducing lattice defects, and improving the quality of the conventional pn junction type LED. Is to provide.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors of the present invention paid attention to the lattice polarity of GaN having a wurtzite structure, and intensively studied the influence of temperature on its decomposition rate and growth rate. As a result, the conventional growth polarity of the GaN layer at about 1000 ° C. is dominated by the (0001) plane (Ga pole), and the growth of the InGaN layer thereon is also the (0001) plane with the same polarity. On the other hand, in the growth at a low temperature of about 820 ° C. or less, the growth of the (0001) plane is slower than the growth of the opposite (000-1) plane (N pole), and the decomposition rate is increased. We have learned that defects are likely to occur and their quality is reduced. The present invention is based on such new knowledge.
[0012]
That is, according to the present invention, in the method for growing a semiconductor crystal film, a GaN layer is grown on a sapphire substrate via a buffer layer, and then an InGaN layer or an InN layer is grown thereon.
A buffer layer is grown on the crystal of the substrate, and a GaN layer having a (000-1) plane orientation is grown on the buffer layer. 780 There is provided a method for growing a semiconductor crystal film, characterized in that the growth is performed at 800 ° C. or lower, and then the growth of an InGaN layer or InN layer whose plane orientation is (000-1) plane is performed at 800 ° C. or lower. .
[0013]
According to the method of the present invention, the GaN layer is formed at a temperature of about 820 ° C. or lower and about 500 ° C. or lower, which is lower than that of the prior art. In this temperature region, the growth polarity of the GaN layer is (000-1) plane (N pole). Becomes dominant. Next, since the InGaN layer or the InN layer on the GaN layer is formed at about 800 ° C. or less, the InN molar fraction y can be increased (for example, about 0.7 or more), and thermal decomposition of InGaN can be prevented.
In addition, since this InGaN layer or InN layer has a GaN layer as a base grown on the (000-1) plane, the growth polarity of the InGaN layer or InN layer is also the same as that of the base layer (000-1). It becomes.
[0014]
Furthermore, in the low temperature region of about 800 ° C. or lower and about 400 ° C. or higher, the growth of the (000-1) plane of the InGaN layer or InN layer is higher than that of the conventional (0001) plane based on the results of the above research. It was confirmed that a high-quality InGaN layer or InN layer can be obtained because the crystal atom arrangement is less likely to occur because the growth rate is high, the decomposition rate is low, and the growth direction is energetically stable. Therefore, the InGaN layer or InN layer having a growth polarity of (000-1) plane has reduced lattice defects as compared with the case of growth of (0001) plane, so that the quality is superior to the conventional one. Become.
[0015]
According to a preferred embodiment of the present invention, the growth of each layer is performed by MOVPE (organometallic compound vapor phase epitaxy), HVPE (hydride vapor phase epitaxy) or MOMBE (organometallic molecular beam epitaxy).
By these growth methods, each layer can be efficiently grown while setting the substrate temperature to a predetermined temperature.
[0016]
The precursor of Ga is GaCl, Ga (CH Three ) Three Or Ga (C 2 H Five ) Three And the precursor of In is In (CH Three ) Three Or In (C 2 H Five ) Three And the precursor of N is ammonia, MNH 2 (Methylamine), DMNH (dimethylamine), TMN (trimethylamine), N 2 H 2 (Hydrazine), (CH Three ) NH-NH 2 (Monomethylhydrazine) or (CH Three ) 2 N-NH 2 (Dimethylhydrazine).
By exciting and decomposing these precursors, the GaN layer, InGaN layer, and InN layer can be grown efficiently.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.
[0018]
FIG. 1 is a schematic diagram of a wurtzite crystal structure (A) and a tetrahedral cluster (B). Group III nitride crystals such as GaN, InGaN and InN usually have a wurtzite crystal structure or a zinc blend type structure. Here, the case of a wurtzite crystal structure will be described.
The wurtzite crystal structure has no center of symmetry and has a (0001) plane (Ga pole) and a (000-1) plane (N pole). As is clear from FIG. 1, the structure in which the group III atom (Ga, In, etc.) and the group V atom (N) are exchanged is one in which the direction of the original crystal is reversed. In these two types of directions, the atomic species appearing on the outermost surface and the bonding arrangement with surrounding atoms are different, and therefore the surface reconstruction structure is different.
In the group III nitride crystal, the direction of growth depends on the type of substrate and other growth conditions. Since the surface structure differs depending on the polarity, the crystal growth process also varies. As a result, a large difference appears in the microstructure and growth surface shape of the obtained epitaxial layer.
[0019]
FIG. 2 is a graph showing the relationship between the decomposition rate of the GaN layer and the temperature obtained in the examples described later. In this figure, the horizontal axis is the temperature (upper axis) and its reciprocal (lower axis), the vertical axis is the decomposition rate of the GaN layer, ● in the figure is the (0001) plane (Ga pole), and ○ is (000-1) It is a plane (N pole).
From this figure, at about 820 ° C., the decomposition rates of the (0001) plane and the (000-1) plane are reversed, the decomposition rate of the (000-1) plane is high on the high temperature side, and (0001) on the low temperature side. It can be seen that the surface decomposition rate is large. In addition, since the vertical axis | shaft in a figure is a logarithm display (exponential function display), it needs to care about that an actual difference has more than twice.
[0020]
FIG. 3 is a graph showing the relationship between the growth rate of the GaN layer and the temperature similarly obtained in Examples described later. In this figure, the horizontal axis is the temperature, the vertical axis is the growth rate of the GaN layer, the ● in the figure is the (0001) plane (Ga pole), and the ◯ is the (000-1) plane (N pole).
From this figure, the growth rate is also about 820 ° C., the (0001) plane and the (000-1) plane are reversed, the growth rate of the (0001) plane is high on the high temperature side, and (000-1) on the low temperature side. It can be seen that the growth rate of the surface is large.
[0021]
2 and 3, it can be seen that the growth rate of the (0001) plane is low and the decomposition rate is high in the temperature range from about 820 ° C. to about 750 ° C. which is lower than that. That is, in this temperature region, the Ga electrode is intensely etched, and on the other hand, the growth rate is slow, and as a result, it is considered that a GaN layer with poor quality grows.
Even in the growth of InN and InGaN, since InN and InGaN are III-V group compound semiconductors having the same crystal structure as GaN, there is a stable surface boundary in the vicinity of about 820 ° C. as in the growth of GaN. By analogy. However, in the case of InGaN and InN, the decomposition vapor pressure is high at a high temperature of about 820 ° C. or higher, and growth cannot be performed under the normal growth conditions of MOVPE and MOBE. Therefore, the original stable growth direction of InGaN and InN is the (000-1) direction, and the growth direction (0001) of InGaN and InN that is currently normally performed cannot be said to be a stable growth direction.
[0022]
Based on the above-described novel findings, the method of the present invention significantly reduces the temperature at which the GaN layer is grown on the sapphire substrate shown in FIG. The growth is performed at about 800 ° C. or lower. As a result, from FIGS. 2 and 3, the growth polarity of the GaN layer is dominant in the (000-1) plane in this temperature region.
In the present invention, the growth of the InGaN layer thereon is performed at about 500 ° C. or lower and about 400 ° C. or higher. Thereby, the growth polarity of the InGaN layer is also the same (000-1) plane.
[0023]
That is, the GaN layer is formed at a temperature lower than about 820 ° C. or lower and about 500 ° C. or lower, and the GaN layer is grown on the (000-1) plane, and then the InGaN layer or InN layer on the GaN layer is about 800 Perform at or below ℃. Thereby, when the InGaN layer or InN layer is grown, the underlying GaN layer is formed on the (000-1) plane, so the growth polarity of the InGaN layer or InN layer is the same as that of the underlying layer (000 -1) Surface.
Also, in the temperature range of about 800 ° C. or lower, the growth of the (000-1) plane is faster than the conventional (0001) plane and the decomposition rate is slower, so the quality is superior to the conventional one. It becomes.
[0024]
In the method of the present invention, each layer is grown by HVPE (hydride vapor phase epitaxy), MOVPE (organometallic compound vapor phase epitaxy), or MOMBE (organometallic molecular beam epitaxy method).
That is, for example, the sapphire substrate is adjusted by a temperature adjusting means (for example, a heater) in the reaction vessel, and the GaN layer is grown at about 820 ° C. or less and about 500 ° C. or more. The InGaN layer and the InN layer are formed at a temperature at which InGaN does not thermally decompose (for example, about 800 ° C. or less).
[0025]
In addition, precursors of In, Ga, and N are sequentially or simultaneously supplied into the reaction vessel from the gas introduction unit. The precursor of Ga is GaCl, the precursor of N is ammonia, MNH 2 (Methylamine), DMNH (dimethylamine), TMN (trimethylamine), N 2 H 2 (Hydrazine), (CH Three ) NH-NH 2 (Monomethylhydrazine) or (CH Three ) 2 N-NH 2 (Dimethylhydrazine) is preferable.
[0026]
【Example】
Examples of the present invention will be described below.
GaN having a wurtzite structure has polarities along the c-axis direction, that is, (0001) plane (Ga pole) and (000-1) plane (N pole). Therefore, it is very important to study the decomposition mechanism of GaN on the cleaning or etching surface. In this example, the decomposition rate with respect to the plane polarity of the GaN single crystal on the sapphire substrate (0001) surface was tested using the in-situ gravity measurement monitoring method (GM method).
[0027]
The test apparatus consists of a vertical reaction tube and a micro weight recorder. This microgravity recording apparatus has 0.004 μg (2.0 cm). 2 3.3 × 10 GaN of area -6 The sensitivity is approximately equivalent to μm. Carrier gas is H 2 And inert gas, and He was used as the inert gas. Hydrogen partial pressure in carrier gas (P H2 ) Is H 2 It changes by changing the ratio of H2 to + He. One side of a mirror-finished GaN substrate (0001) has a thickness of 1000 mm. 2 Covered with a layer and suspended from the microbalance with silica fibers. Thereby, the polarity dependence of the GaN substrate (0001) surface can be measured.
[0028]
FIG. 2 is a graph showing the relationship between the decomposition rate of the GaN layer and the temperature obtained in this test.
As is clear from this figure, H 2 Carrier gas environment (P H2 The decomposition rate in 1) increases exponentially with the increase in temperature in the temperature range of 650 ° C. to 950 ° C., regardless of the surface polarity. It was also revealed that the decomposition rate itself differs depending on the lattice polarity. In the low temperature range of 820 ° C. or lower, the decomposition rate of the (0001) plane of GaN is faster than that of the (000-1) plane. On the other hand, in the high temperature region from 850 ° C. to 950 ° C., the decomposition rate of the (000-1) plane of GaN is faster than that of the (0001) plane. The reason for this result is due to the difference in activation energy in the decomposition process of the (0001) and (000-1) planes of GaN.
[0029]
Further, the relationship between the decomposition rate of the GaN plane (0001) and (000-1) plane and the hydrogen partial pressure was examined from 600 ° C. to 950 ° C. As a result, it became clear that the decomposition rate of GaN is proportional to the 3/2 power of the hydrogen partial pressure regardless of the surface polarity in the low temperature region below 850 ° C. On the other hand, in the high temperature region of 850 ° C. or higher, it was revealed that the decomposition rate is proportional to the 1/2 power of the hydrogen partial pressure regardless of the polarity. This means that the rate-limiting reaction for controlling the decomposition rate is different between the low temperature region and the high temperature region. On the other hand, GaN (s) and H 2 From the thermodynamic analysis of the reaction with (g), the main gas phase molecular species generated in this reaction are NH Three It is clear that the rate-limiting reaction by the reaction between the low-temperature region and hydrogen in the high-temperature region is expressed by the equations (1) and (2), respectively.
GaN (surface) + 3 / 2H 2 (G) → Ga (surface) + NH Three (G) ... (1) (low temperature region)
GaN (surface) + 1 / 2H 2 (G) → N (surface) + GaH (g) (2) (high temperature region)
[0030]
On the other hand, since hydrogen gas is used as a carrier gas during the growth of GaN and hydrogen is generated by the growth reaction of GaN, it is necessary to consider that the reaction between the GaN surface and hydrogen occurs simultaneously. is there. Furthermore, the growth rate actually obtained is considered to be the difference between the precipitation reaction and the decomposition reaction. This is also apparent from the relationship between growth and temperature in FIG.
[0031]
From the above results, it is clear that in decomposition and growth, the GaN (000-1) plane is dominant in the low temperature region, and the GaN (0001) plane is dominant in the high temperature region.
[0032]
Such an invention clarified the following facts, as well as the growth conditions for obtaining high-quality crystals of InGaN and InN.
[0033]
Fact 1: In growth using a nonpolar substrate crystal such as sapphire, the growth plane orientation of GaN grown on sapphire is determined particularly by the growth temperature. The relationship between the temperature and the growth plane orientation is the (000-1) plane in the low temperature region and the (0001) plane in the high temperature region. In general, GaN uses a high temperature region around 1000 ° C., and (0001) plane growth is expected to dominate. In fact, it has been clarified that the (0001) Ga termination plane is the growth plane. .
[0034]
Fact 2: When a GaAs (111) crystal is used as the substrate crystal, the GaAs (111) A plane is the GaN (0001) plane, the GaAs (111) B plane is the (Gan (000-1) plane, the III group and V The bonding state of group V and group V atoms is equivalent, so that when GaAs (111) A plane is used, good growth of GaN is possible by growth at 1000 ° C. or higher after buffer layer growth at about 500 ° C. On the other hand, in the growth at 850 ° C. or higher after the buffer layer growth at about 500 ° C. using the GaAs (111) B surface, good GaN is obtained. No growth can be obtained, and the growth surface of 1 micron or more is (0001), and it is clear that the growth direction is reversed at the initial stage of growth.
[0035]
(Note 1) Growth on the GaAs (111) A plane Kumagai et al. Jpn. J. et al. Appl. Phys. , 39 (2000) L149 and Y.M. Kumagai et al. Jpn. J. et al. Appl. Phys. , 39 (2000) L703. It is clear from.
[0036]
(Note 2) The growth plane measurement is clear from the following announcement using our sample. 2001 Spring Joint Lecture on Applied Physics 29a-L-2 Ogawa et al. (Group of Professor Akimoto, Faculty of Engineering, Nagoya University)
(Contents: In GaN growth on GaAs (111) A and GaAs (111) B planes, the surface of the GaN buffer layer of 100 nm or less is the (0001) and (000-1) planes, respectively. The surface after GaN growth of 1 micron or more at 1000 ° C. was (0001) plane.)
[0037]
Fact 3: The surfaces obtained by the growth experiment using the single crystal GaN substrate shown in FIG. 3 are GaN (0001) plane and GaN (000--) on the GaN (0001) plane and GaN (000-1) plane, respectively. 1) A plane was obtained regardless of the growth film thickness.
[0038]
Fact 4: Conventional InGaN and InN are grown in a low temperature region of 800 ° C. or lower on a GaN crystal grown at about 1000 ° C. after growing a buffer layer on the sapphire substrate crystal at about 500 ° C. For this reason, InGaN or InN having a stable (000-1) growth surface on the (0001) growth surface is grown on the (0001) growth surface, which is induced by defects due to instability of atomic arrangement or the defects. Composition separation occurs. For this reason, it is difficult to grow a high-quality crystal. InGaN or InN having a large In composition, a crystal that can obtain optical characteristics has not been obtained.
[0039]
Fact 5: In the growth of InGaN or InN for the purpose of a laser element or the like, a GaN single crystal substrate manufactured by a thick film growth using a GaN single crystal substrate, a sapphire substrate, a GaAs substrate or the like prepared by a high pressure method or a sublimation method is provided. It is used. Also in this case, since the growth of GaN and AIN is grown at about 1000 ° C. in the initial stage, the GaN (0001) plane is used as the growth plane, and the same phenomenon as the fact 4 described above appears.
[0040]
Example 1:
(1) In MOVPE growth using a sapphire substrate, after growing a buffer layer at about 500 ° C., grow about 2 microns of GaN at 1000 ° C., and then grow 0.5 μm of In0.2Ga0.8N at 780 ° C. went. On the other hand, (2) MOVPE growth is similarly performed using a sapphire substrate. After the buffer layer is grown at about 500 ° C., GaN of about 2 microns is grown at 800 ° C., and then 0.5 μm of In0.2GaO. Growing 8N. By surface analysis of the growth surface, the surface obtained in (1) was the (0001) plane, and (2) was the (000-1) plane. As a result of PL (photoluminescence) measurement at room temperature, the half-value width of the high-temperature GaN-grown sample was 165 meV, whereas the low-temperature GaN-grown sample was halved to 77 meV and the crystal quality was improved.
[0041]
Example 2:
Using the GaAs (111) B surface as the substrate crystal, the buffer layer was grown at about 500 ° C. by MOVPE growth, and then GaN was grown at 1.5 μm at 780 ° C., and then 0.6 μm at 780 ° C. In 0.3 Ga 0.7 N grew. It was confirmed that the growth surface was a (000-1) plane. In addition, it has been clarified that in the grown InGaN mixed crystal, a cluster having a large In composition, which is often observed in the case of the (0001) growth surface, is not observed, and a uniform mixed crystal can be obtained.
[0042]
Example 3:
Using the GaAs (111) B surface as the substrate crystal, the buffer layer was grown at about 500 ° C. by MOVPE growth, and then GaN was grown at 1.5 μm at 780 ° C., and then 0.2 μm at 650 ° C. In 0.6 Ga 0.4 N grew. It was confirmed that the growth surface was a (000-1) plane. Further, it was revealed that the grown InGaN mixed crystal did not show phase separation and a uniform mixed crystal was obtained. As a result of X-ray diffraction, the half value width of about 2.1 min 0.6 Ga 0.4 It was found that N was obtained. On the other hand, a MOVPE growth using a sapphire substrate or a GaAs (111) A-plane substrate is carried out, a buffer layer is grown at about 500 ° C., GaN is grown at about 950 ° C., and In is then grown at 650 ° C. 0.6 Ga 0.4 Attempts were made to grow N, but phase separation occurred and a uniform InGaN mixed crystal could not be obtained.
[0043]
Example 4:
Using the GaN single crystal substrate (000-1) surface as the substrate, GaN was grown at 2 microns at 750 ° C., then In 0.2 Ga 0.8 N mixed crystals were grown to 0.15 microns. A uniform composition is obtained without instability of the composition in the InGaN mixed crystal. On the other hand, in the growth based on the GaN (0001) plane, the existence of a cluster having a large In composition in the mixed crystal was revealed. Further, it was found by photoluminescence measurement that the FWHM of GaN (000-1) plane growth was small and the quality was good.
[0044]
Example 5:
Using the GaN (000-1) plane as a substrate crystal, GaN was grown by 1.5 μm at 780 ° C. by MOVPE growth, and on that, 0.2 μm InGaN was grown at 650 ° C. It was confirmed to be a growth surface (000-1) plane. Further, it was revealed that the grown InGaN mixed crystal did not show phase separation and a uniform mixed crystal was obtained. This was confirmed by X-ray diffraction and photoluminescence.
[0045]
According to the above-described method of the present invention, since the GaN layer is formed at a temperature lower than about 820 ° C. or lower and about 500 ° C. or higher, the growth polarity of the GaN layer is (000-1) plane (N Pole) becomes dominant. Next, since the InGaN layer or the InN layer on the GaN layer is formed at about 800 ° C. or less, the InN molar fraction y can be increased (for example, about 0.7 or more), and thermal decomposition of InGaN can be prevented.
In addition, since this InGaN layer or InN layer has a GaN layer as a base grown on the (000-1) plane, the growth polarity of the InGaN layer or InN layer is also the same as that of the base layer (000-1). It becomes.
Furthermore, in the low temperature region of about 800 ° C. or lower and about 400 ° C. or higher, the growth of the (000-1) plane of the InGaN layer or InN layer is higher than that of the conventional (0001) plane based on the results of the above research. It was confirmed that the speed was high and the decomposition speed was slow. Therefore, the InGaN layer or InN layer having a growth polarity of (000-1) plane has reduced lattice defects as compared with the case of growth of (0001) plane, so that the quality is superior to the conventional one. Become.
[0046]
In addition, this invention is not limited to the Example and embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.
[0047]
【Effect of the invention】
As described above, the semiconductor crystal film growth method of the present invention improves the crystal structure, increases the growth rate, reduces the lattice defects, and improves the quality of the conventional pn junction type LED. It has excellent effects such as
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a wurtzite crystal structure (A) and a tetrahedral cluster (B).
FIG. 2 is a relationship diagram between a decomposition rate of a GaN layer and temperature.
FIG. 3 is a relationship diagram between the growth rate of a GaN layer and temperature.
FIG. 4 is a cross-sectional structure diagram of a blue LED using InGaN.
FIG. 5 is a relationship diagram of main semiconductor band gaps and lattice constants.
FIG. 6 is a graph showing the relationship between the molar fraction y of InN in InGaN and the equilibrium temperature.
FIG. 7 is a schematic view of a conventional method for growing a semiconductor crystal film.
FIG. 8 is a schematic diagram of a substrate temperature program of MOVPE (organometallic compound vapor phase epitaxy) of GaN using a low temperature deposition layer.
FIG. 9 is a schematic view of the substrate temperature dependence of the growth rate of the binary compounds InN, GaM, and AlN.
[Explanation of symbols]
1 Sapphire substrate, 2 reactive gas injection tube, 3 sub-injection tube,
4 susceptor, 5 shaft, 6 reaction vessel, 7 heater,
8 exhaust port, 9 radiation thermometer

Claims (3)

サファイヤ基板上にバッファ層を介してGaN層を成長させ、次いで、その上にInGaN層又はInN層を成長させる半導体結晶膜の成長方法において、
前記基板の結晶上にバッファ層を成長させ、該バッファ層上に面方位が(000−1)面であるGaN層の成長を780℃以下,500℃以上で行い、次いで面方位が(000−1)面であるInGaN層又はInN層の成長を800℃以下で行う、ことを特徴とする半導体結晶膜の成長方法。
In a method for growing a semiconductor crystal film, a GaN layer is grown on a sapphire substrate via a buffer layer, and then an InGaN layer or an InN layer is grown thereon.
A buffer layer is grown on the crystal of the substrate, a GaN layer having a (000-1) plane orientation is grown on the buffer layer at 780 ° C. or lower and 500 ° C. or higher, and then the plane orientation is (000− 1) A method for growing a semiconductor crystal film, comprising growing an InGaN layer or an InN layer as a surface at 800 ° C. or lower.
前記各層の成長は、MOVPE(有機金属化合物気相成長法)、HVPE(ハイドライド気相成長法)又はMOMBE法(有機金属分子ビームエピタキシー法)による、ことを特徴とする請求項1に記載の半導体結晶膜の成長方法。  2. The semiconductor according to claim 1, wherein the growth of each layer is performed by MOVPE (organometallic compound vapor deposition), HVPE (hydride vapor deposition), or MOMBE (organometallic molecular beam epitaxy). Crystal film growth method. 前記Gaの前駆体はGaCl、Ga(CH又はGa(Cであり、Inの前駆体はIn(CH又はIn(Cであり、Nの前駆体はアンモニア、MNH(メチルアミン)、DMNH(ジメチルアミン)、TMN(トリメチルアミン)、N(ヒドラジン)、(CH)NH−NH(モノメチルヒドラジン)、又は(CHN−NH(ジメチルヒドラジン)である、ことを特徴とする請求項1に記載の半導体結晶膜の成長方法。The Ga precursor is GaCl, Ga (CH 3 ) 3 or Ga (C 2 H 5 ) 3 , the In precursor is In (CH 3 ) 3 or In (C 2 H 5 ) 3 , and N Are precursors of ammonia, MNH 2 (methylamine), DMNH (dimethylamine), TMN (trimethylamine), N 2 H 2 (hydrazine), (CH 3 ) NH—NH 2 (monomethylhydrazine), or (CH 3 ). The method for growing a semiconductor crystal film according to claim 1, wherein the method is 2 N—NH 2 (dimethylhydrazine).
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