JP4100759B2 - Method for manufacturing compound semiconductor device - Google Patents

Description

【００１５】
表２に、５３０℃成長のＧａ_0.965 Ｉｎ_0.05Ｎ_y Ａｓ_1-y の蛍光強度と窒素組成ｙの相関関係（測定室温）を示す。
【００１６】
【表２】

【００１７】
表２から明らかなように、上述と同様の傾向がＧａＩｎＮＡｓでも確認されている。
【００１８】
表３に、５３０℃成長のＧａＮＡｓの比抵抗と窒素組成の相関関係（測定室温）を示す。
【００１９】
【表３】

【００２０】
表４に、５３０℃成長のＧａＩｎＮＡｓの比抵抗と窒素組成のと相関関係（測定室温）を示す。
【００２１】
【表４】

【００２２】
表３および表４から明らかなように、ＧａＮ_x Ａｓ_1-x 、ＧａＩｎＮＡｓともに窒素濃度が高くなるに従い、比抵抗が大きくなり、電気特性が劣化する。
【００２３】
このように、光学特性、電気的特性が悪い薄膜結晶を、前述の発光素子として用いた場合、素子の動作特性、信頼性を著しく劣化させる。受光素子の場合、受光感度が低くなり、微弱な光の検出ができない。また、発光素子の場合、光の発光強度が弱くなる。また、特に半導体レーザでは連続的なレーザ光発振ができない。発光受光素子、電子素子いずれの場合も、抵抗率が高い層が多層膜中に存在すると、電気的に動作しない場合がある。
【００２４】
それゆえに、この発明の目的は、実用に十分な水素不純物が少なく、高い光学特性、電気特性を有するＧａ_1-xＩｎ_xＮ_yＡｓ_1-y、ＧａＮ_yＡｓ_1-y結晶を有する化合物半導体装置の製造方法を提供することにある。
【００２５】
この発明の他の目的は、水素不純物が多い場合も、窒素−水素結合を切断する熱処理、水素濃度を低減する熱処理により、結晶の高品質化が計られ、電気特性、光学特性が良好な光学素子を得ることができる製造方法を提供することにある。
【００２６】
この発明のさらに他の目的は、水素不純物が少ない場合も、熱処理により窒化物結晶固有の問題を解決し、良好な結晶を提供することができる製造方法を提供することにある。
【００２７】
この発明のさらに他の目的は、結晶成長に引続いて、熱処理を行なうことで、結晶成長の省時間と省エネルギにも有利であり、素子の大量生産が可能となる製造方法を提供することにある。
【００２８】
【課題を解決するための手段】
本発明の化合物半導体装置の製造方法は、光ファイバ通信の搬送波に用いる赤外光を出射し、該赤外光を生じる活性層がＩＩＩ−Ｖ族混晶半導体に窒素および砒素を含有させた半導体層から成る化合物半導体装置の製造方法において、ＧａＡｓ半導体基板を準備する工程と、前記ＧａＡｓ半導体基板の上に、Ｇａ_１−ｘＩｎ_ｘＮ_ｙＡｓ_１−ｙ（０＜ｘ≦０．３５，０＜ｙ≦０．０５）および／またはＧａＮ_ｙＡｓ_１−ｙ（０＜ｙ≦０．０６）からなる半導体層を活性層としてエピタキシャル成長により形成する工程と、前記活性層をエピタキシャル成長した後に前記ＧａＡｓ半導体基板を、非酸化性ガス雰囲気中、ヒ素系ガス雰囲気中、リン系ガス雰囲気中、または真空中で、８５０℃以上１１００℃以下で熱処理することにより、前記活性層中の水素濃度を１ｃｍ^３あたり５×１０^１８個以下とする工程と、を備える。
【００２９】
上記の方法によれば、ＧａＡｓ半導体基板の上記半導体層について熱処理条件と水素濃度との関係を把握しておき、Ｇａ_1-xＩｎ_xＮ_yＡｓ_1-y（０＜ｘ≦０．３５，０＜ｙ≦０．０５）および／またはＧａＮ_yＡｓ_1-y（０＜ｙ≦０ . ０６）中の水素濃度が１ｃｍ³あたり５×１０¹⁸個以下になる熱処理条件で熱処理を行うことができる。この結果、製品の水素濃度を上記濃度以下に確実にできるので、これらの半導体層の発光特性を向上し、また電気抵抗を減少させることができる。
【００３０】
この発明の参考となる化合物半導体装置の製造方法によれば、まず、ＧａＡｓ半導体基板を準備する。上記ＧａＡｓ半導体基板の上に、Ｇａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y（０＜ｘ≦０．３５，０＜ｙ≦０．０５）および／またはＧａＮ_y Ａｓ_1-y （０＜ｙ≦０ . ０６）からなる、ＩＩＩ−Ｖ族混晶半導体に窒素を含有させたものであり、１ｃｍ³あたり５×１０¹⁸個以上の水素を含む半導体層を形成する。上記半導体層を、非酸化性雰囲気中、ヒ素系ガス雰囲気中、リン系ガス雰囲気中、または真空中で、５００℃以上８００℃未満で熱処理し、それによって上記半導体層中の水素不純物と窒素の結合を切断する。
【００３１】
この発明の参考となる化合物半導体装置の製造方法によれば、まず、ＧａＡｓ半導体基板を準備する。上記ＧａＡｓ半導体基板の上に水素濃度が１ｃｍ³あたり５×１０¹⁸個以下にされた、Ｇａ_1-xＩｎ_x Ｎ_y Ａｓ_1-y （０＜ｘ≦０．３５，０＜ｙ≦０．０５）および／またはＧａＮ_yＡｓ_1-y （０＜ｙ≦０ . ０６）からなる、ＩＩＩ−Ｖ族混晶半導体に窒素を含有させた半導体層を形成する。上記半導体層を、非酸化性ガス雰囲気中、ヒ素系ガス雰囲気中、リン系ガス雰囲気中、または真空中で、５００℃以上１１００℃未満で熱処理し、それによって、結晶特性と光学特性の改善を行なう。
【００３２】
【発明の実施の形態】
特開平９−２８３８５７号公報に示されているようにＧａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y 薄膜結晶を成長する場合、Ａｓ原子が基板および薄膜の表面から脱離しやすい。このため、脱離を防止するため、低温での成長が必要である。このような低温では、ヒ素の脱離が防止できるとともに、窒素原料が結晶の表面に吸着しやすくなり、窒素濃度が高くできる利点があるが、半面、不純物も吸着しやすくなり、結晶中の不純物濃度が窒素濃度に比例して高くなる。
【００３３】
特に、有機金属気相成長法（ＯＭＣＶＤ）では、用いる有機原料ガスのガス分子が水素原子で構成されるものが多い。そのため、薄膜結晶中に水素が混入する問題がある。水素の混入の過程には、原料ガスそのもの、原料ガスが分解する途中の中間生成物、原料から分解した後の水素原子が、薄膜結晶中に取込まれることが考えられる。この水素が不純物として振る舞い、光学的に特性と電気的特性を悪化させたと考えられる。実際に、Ｇａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y およびＧａＮ_y Ａｓ_1-y 結晶中で、水素が上記の特性を劣化させる結果はこれまで報告されていないが、他のＩＩＩ−Ｖ族混晶半導体では調べられた例がある。
【００３４】
ＧａＡｓ結晶中では、水素がドーピング原子と結合し、ドーピング原子が有する正あるいは負の電荷を打消し、電気的に不活性になる例が報告されている（J. I. Pankove, N. M. Johnson: Hydrogen in Semiconductors, 1996, Academic Press）。また、ＧａＰ結晶中のＮ原子が水素と結合していると、光学特性を劣化させる例が報告されている（Jorg Weber他: Mat. Res. Soc. Sym. Proc. vol.104, p.325）。なお、水素原子により光学特性が劣化する機構については、未解明である。
【００３５】
この点から、作製したＧａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y ，ＧａＮ_y Ａｓ_1-y 薄膜結晶の光学特性と水素濃度の相関関係を比べると、図２および図３の結果が得られた。図２は、ＧａＮＡｓの場合であり、図３はＧａ_0.9 Ｉｎ_0.1 Ｎ_y Ａｓ_1-y の場合である。それぞれの図は、窒素濃度に対する水素濃度の関係と、それぞれの光学特性を示している。図中の○印は実用上十分な蛍光強度を有する試料を示し、×印は蛍光強度が低く、実用に十分でない試料を示す。現在レーザダイオードに利用されているＩｎＰ基板上に成長したＧａ_0.25Ｉｎ_0.75Ａｓ_0.54Ｐ_0.46結晶の蛍光強度と比較して１／２０以上の強度を有するものを基準にした。水素と窒素の濃度は、２次イオン質量分光法（ＳＩＭＳ：Secondary Ion Mass Spectroscopy ）により測定した。本明細書では、比較となるＧａＩｎＰＡｓの強度を２０として、それに対するＧａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y ，ＧａＮ_y Ａｓ_1-y 薄膜結晶の蛍光強度を示している。すなわち、蛍光強度が１以上であれば、実用に適していると考えられる。
【００３６】
図２および図３中、補助線Ａ１、Ａ２、Ｂ１、Ｂ２、Ｃ１、Ｃ２は、それぞれ５３０℃、５５０℃、６００℃で成長した場合の、窒素濃度と水素濃度の関係を示している。窒素濃度に比例して、水素濃度が上昇する傾向が確認できた。また、成長温度を上げるに従い、水素濃度が下がることが確認できた。これらの図からわかるように、薄膜結晶から実用に十分な蛍光強度を得るためには水素濃度が１ｃｍ³ あたり５×１０¹⁸個以下にする必要がある。
【００３７】
蛍光特性が良好でないＧａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y ，ＧａＮ_y Ａｓ_1-y 薄膜結晶については、結晶内に存在する水素の結合状態をフーリエ変換赤外分光法（ＦＴ−ＩＲ）により測定した。以下にその一例として、ＧａＡｓ基板上に、ＧａＮ_0.012 Ａｓ_0.988 結晶を０．５μ成長した試料の例を示す。このときの水素濃度は、１ｃｍ³ あたり１．５×１０¹⁹個であった。なお、ここで挙げた組成のＧａＮＡｓの測定例は、いくつか実施したものの中の一例である。
【００３８】
波数２９５０ｃｍ^-1の位置に、明瞭な吸収ピークが確認された。このピークは、結晶中の窒素と水素が原子結合している場合にのみ（Ｎ−Ｈ結合がある場合）観察される。
【００３９】
この試料を、５００、５５０、６００、７００、８００℃で窒素雰囲気内で熱処理した場合の、吸収ピークと蛍光強度の変化を測定した。結果を図４に示す。
【００４０】
図４に示されているように、加熱なしの場合と比較して、温度を上げるに従い、吸収ピークが小さくなることがわかる。７００℃の熱処理により、吸収ピークがなくなるとともに、十分な蛍光強度が得られることがわかる。すなわち、水素濃度は、１ｃｍ³ あたり５×１０¹⁸個より大きい場合でも、５００〜８００℃の温度範囲で熱処理を施すことで、結晶中の窒素と水素の原子結合が切断され（Ｎ−Ｈ結合が切れ）、実用に十分な蛍光強度が得られることがわかる。ガス雰囲気は、水素、窒素、アルゴン、ヘリウムの限られた非酸化性雰囲気中、アルシンなどのヒ素系ガス中、フォスフィンなどのリン系ガス中、あるいは真空中が好ましい。雰囲気ガスは、上記のガスを混合したものでもよい。熱処理の時間は１０秒から２４時間がよい。請求項１に定義される構造の最上層が、ＧａＡｓ、ＡｌＧａＡｓ、ＩｎＧａＡｓなどのヒ素を含んだ半導体である場合、熱処理による表面からのヒ素抜けを防ぐため、アルシン、ターシャリブチルアルシンなどのヒ素系ガス中で熱処理を施すことが望ましい。同様に、最上層が、ＧａＩｎＰ、ＡｌＧａＩｎＰ、ＡｌＩｎＰ、ＩｎＧａＡｓＰなどのリンを含んだ半導体である場合、熱処理による表面からのリン抜けを防ぐため、フォスフィン、ターシャリブチルフォスフィンなどのリン系ガス中で熱処理を施すことが望ましい。
【００４１】
熱処理後に実施したＳＩＭＳ分析から、５００〜８００℃の熱処理では、水素と窒素の結合を切ることができるが、水素濃度を低減することはできない。そのため、結晶中の高濃度の水素が窒素と再結合し、光学特性、電気的特性を再劣化させる。そのため、８００〜１１００℃での熱処理をすることで、Ｇａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y 、ＧａＮ_y Ａｓ_1-y 薄膜結晶中の、水素と窒素の結合を切断し、水素を結晶から除去できる。これにより、信頼性が高い素子が作製され得る。ガス雰囲気は、水素、窒素、アルゴン、ヘリウムの限られた非酸化性雰囲気中、アルシンなどのヒ素系ガス中、フォスフィンなどのリン系ガス中、あるいは真空中が好ましい。雰囲気ガスは、上記のガスを混合したものでもよい。熱処理の時間は１０秒から２４時間がよい。
【００４２】
この熱処理は、成長炉内で多層構造成長後に、室温まで冷却した後、再加熱する方法と成長炉内で多層構造成長後に引続いて行なう方法とがある。成長炉内で行なう方法により、信頼性が高い半導体装置を効率よく安価に形成できる。
【００４３】
これに加えて、Ｇａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y 、ＧａＮ_y Ａｓ_1-y は原子半径が大きく異なる元素によって構成される混晶半導体であるため、均一な組成の結晶を得ることが非常に難しい。
【００４４】
表５にＩＩＩ族、Ｖ族元素の原子半径を示す。
【００４５】
【表５】

【００４６】
表５を参照して、他のＩＩＩ族元素、Ｖ族元素と窒素では原子半径が大きく異なる。窒素とインジウムでは原子半径が約２倍も異なる。原子半径が異なる原子により混晶半導体を成長すると、部分的に歪みが発生し、良好な結晶を得ることは難しい。これは、用いている材料の組合せに起因する問題であり、この窒化物材料固有の問題である。水素濃度が５×１０¹⁸個以下の場合でも、５００〜１１００℃の熱処理により、結晶性が改善され、特性が良好な素子が作製可能である。
【００４７】
本発明に係る化合物半導体装置によれば、実用に十分な水素不純物が少なく、高い光学特性、電気特性を有するＧａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y 、ＧａＮ_y Ａｓ_{1- y} 結晶を有する光学素子、電子素子が得られる。ここで、実用に十分な水素不純物濃度は５×１０¹⁸個以下である。
【００４８】
また、この発明によれば、水素不純物が多い場合も、窒素−水素結合を切断する熱処理、水素濃度を低減する熱処理により、結晶の高品質化が図られ、電気特性、光学特性が良好な光学素子を得ることができる。
【００４９】
また、水素不純物が少ない場合も、熱処理により窒化物結晶固有の問題を解決し、良好な結晶を得ることができる。
【００５０】
さらに、結晶成長に引続いて熱処理を行なうことで、結晶成長の省時間と省エネルギにも有利であり、素子の大量生産が可能である。
【００５１】
【実施例】
実施例１
成長には、石英製の横型反応炉を用いた。基板として、半絶縁性ＧａＡｓ（００１）基板を用いた。ＩＩＩ族のＧａ，Ｉｎ原料としてトリエチルガリウム（ＴＥＧ）、トリメチルインジウム（ＴＭＩｎ）を、Ｖ族のＮ，Ａｓ，Ｐ原料としてジメチルヒドラジン（ＤＭＨｙ）、ターシャリブチルアルシン（ＴＢＡｓ）、ターシャリブチルフォスフィン（ＴＢＰ）を用いた。キャリアガスには水素を用いた。成長炉内の圧力は、７６Ｔｏｒｒに設定した、成長温度は、５３０℃、５５０℃、６００℃の３水準で変えた。
【００５２】
以下の条件で、ＧａＡｓ（００１）基板に格子整合したＧａ_0.9 Ｉｎ_0.1 Ｎ_0.035 Ａｓ_0.965 結晶を得ることができた。［ＴＢＡｓ］／（［ＴＥＧ］＋［ＴＭＩ］）モル供給比＝１．８で固定として、成長温度５３０、５５０、６００℃では、［ＤＭＨｙ］／（［ＤＭＨｙ］＋［ＴＢＡｓ］）モル供給比を、それぞれ０．９８，０．９８２，０．９８５とすることでＧａＡｓ（００１）基板に格子整合した。また、それぞれの成長温度で、上記のモル供給比を増減させることによって窒素濃度を調整した。
【００５３】
図２，３および図６，７には結果が挙げられていないが、ＧａＡｓ（００１）基板に格子整合した、Ｉｎ濃度がより高いＧａ_0.85Ｉｎ_0.15Ｎ_0.053 Ａｓ_0.947 結晶は、［ＴＢＡｓ］／［ＴＥＧ］＋［ＴＭＩ］）モル供給比＝２で固定として、成長温度５３０、６００℃では、［ＤＭＨｙ］／（［ＤＭＨｙ］＋［ＴＢＡｓ］）モル供給比を、それぞれ０．９８４，０．９８７とすることで、ＧａＡｓ（００１）基板に格子整合したＧａＩｎＮＡｓ結晶が得られた。
【００５４】
次に、ＧａＮＡｓ結晶の成長方法は以下のとおりである。［ＴＢＡｓ］／［ＴＥＧ］モル供給比＝５で固定とし、［ＤＭＨｙ］／（［ＤＭＨｙ］＋［ＴＢＡｓ］）モル供給比を０．２５６−０．９の間で窒素濃度に合わせて変化させた。成長温度は、５３０，５５０，６００℃の３水準を用いた。
【００５５】
図５に、実際に作製した素子構造を示す。（ａ）は、光学特性評価用ダブルヘテロ（ＤＨ）構造を示す図であり、（ｂ）は電気的特性評価用単層構造を示す図である。
【００５６】
光学特性の測定には、図５（ａ）の、半導体レーザの構造を簡略化したＧａＩｎＮＡｓおよびＧａＮＡｓ薄膜結晶の、上下がＧａＡｓで挟まったダブルヘテロ構造（ＤＨ構造）を用いた。これを用い、光学特性の変化を、蛍光の強度を測定することにより調べた。簡略化した構造を用いた理由は、図１に示すような実際のレーザ構造を用いると、ＧａＩｎＮＡｓおよびＧａＮＡｓ結晶からの蛍光が上下の材料種が異なる層で散乱吸収され、測定が精密に行なえないためである。
【００５７】
上下のＧａＡｓ層は、１００ｎｍとし、ＧａＩｎＮＡｓおよびＧａＮＡｓ層は５００ｎｍとした。また、電気的特性測定用には、図５（ｂ）に示す、受光ダイオードを簡略化したＧａＩｎＮＡｓおよびＧａＮＡｓ薄膜結晶単層を用いた。これは、実際の構造を用いると、ｐ型とｎ型が接合を形成する実際の構造では、他の層の特性の変化も計測されるためである。測定は、室温でホール測定法と呼ばれる方法を用いた。ＧａＩｎＮＡｓ層およびＧａＮＡｓ層の厚みは５００ｎｍとした。
【００５８】
作製した試料の蛍光強度の測定には、アルゴンレーザで発生する波長５１４ｎｍの光を照射し、結晶から出てくる蛍光強度をゲルマニウム製検出器により評価した。また、ＳＩＭＳによる不純物濃度の分析には、セシウムイオンを試料に照射し、スパッタされる水素負イオン（Ｈ^- ）を検出した。絶対濃度は、同時に検出されるＡｓイオンと比較校正することで算出した。測定系の校正は、別途作製したＮイオンをＧａＡｓ薄膜に注入した校正試料を用い注意深く行なった。
【００５９】
実施の形態で説明した図２と図３を参照して、ＧａＮＡｓでは、６００℃での成長の場合、窒素濃度を１．８×１０¹⁹〜１．５×１０²¹の範囲で変化させたが、水素濃度は２．９×１０¹⁷〜１．１×１０¹⁸と低濃度となっている。この試料の蛍光強度は、ＩｎＧａＡｓＰの強度を２０とすると、ＧａＮＡｓは２．３〜２６となり、どの窒素濃度においても実用可能な蛍光強度が得られている。
【００６０】
一方、５３０℃では、水素濃度と蛍光強度に強い相関がある。窒素濃度が１．８×１０¹⁹〜１．０×１０²⁰と低い範囲では、水素濃度は３．８×１０¹⁷〜２．７×１０¹⁸であり、蛍光強度も１．８〜１４となった。一方、窒素濃度が１．９×１０²⁰〜５．５×１０²⁰と高い範囲では、水素濃度が５．９×１０¹⁸〜１．９×１０¹⁹となり、蛍光強度も０．０９〜０．８７と低くなり、実用に十分ではない。
【００６１】
ＧａＩｎＮＡｓをＧａ_0.9 Ｉｎ_0.1 Ｎ_0.035 Ａｓ_0.965 の組成で成長した場合、成長温度５３０、５５０、６００℃では、窒素濃度が７．２×１０²⁰で水素濃度６．２×１０¹⁹、８．９×１０¹⁸、８．２×１０¹⁷となり、それぞれ蛍光強度は０（検出限界以下）、０、２．４となる。したがって、水素濃度が５×１０¹⁸以下の場合のみ、実用に十分な蛍光強度が得られている。
【００６２】
実施例２
実施例１で挙げた成長方法で成長温度を５３０℃とした場合、Ｇａ_1-x Ｉｎ_x Ｎ_y Ａｓ_1-y ，ＧａＮ_y Ａｓ_1-y ともに結晶中の水素濃度が１ｃｍ³ あたり５×１０¹⁸個以上となる（図２と図３参照）。
【００６３】
この条件で、実施例１で説明した測定構造を成長終了後、下記の条件で再加熱し、光学特性と電気的特性の測定を行なった。
【００６４】
この熱処理では、表面から、Ａｓが蒸発するのを防止するため、プラズマＣＶＤ法により、ＳｉＮ膜を１００ｎｍ成長した。ＳｉＮ膜は、熱処理後に５％フッ酸で除去した。
【００６５】
上記の構造を、水素雰囲気中、圧力を７６Ｔｏｒｒにし、熱処理した。熱処理には、石英製の加熱炉を用いた。以下に、ＧａＮ_0.012 Ａｓ_0.988 の試料を熱処理した例を示す。熱処理温度が３００、５００、６００、６５０、７００、７５０、８００、８５０、９００、１１００℃の１０水準で行なった例を示す。室温から最高到達温度までの昇温速度は１分間あたり８０℃である。熱処理温度に達した後、温度を１０分間保持する。この後、室温まで１分間あたり８０℃の降温速度で室温まで冷却する。
【００６６】
表６に、熱処理温度に対する、蛍光の強度を示す。
【００６７】
【表６】

【００６８】
未処理の場合に比較し、３００℃以上７００℃以下までは、熱処理温度を上げるに従い、蛍光強度が向上する。７００℃より高い温度では、蛍光強度が下がるが、未処理の場合に比較して蛍光強度が高い。
【００６９】
実施の形態で説明したように、図４は、この試料中の水素−窒素結合、蛍光強度の変化を示す。７００℃の熱処理で水素−窒素結合は完全に切断され、実用に十分な蛍光強度が得られることがわかる。表６に示すように、水素濃度は７００℃の熱処理では低下せず、８００℃以上の熱処理が必要であることがわかる。
【００７０】
次に、ＧａＮＡｓ，ＧａＩｎＮＡｓの２試料を、上記の実験で蛍光強度が最高であった温度７００℃で熱処理し、熱処理時間を１０秒から２時間まで変化させた。
【００７１】
結果を表７に示す。
【００７２】
【表７】

【００７３】
ここでは、同じ試料を繰返し熱処理し、横軸の熱処理時間は到達温度での積算時間である。用いた装置は、急速加熱が可能なrapid thermal annealing （ＲＴＡ）装置を用いた。雰囲気は窒素中で、圧力は７６０Ｔｏｒｒとした。
【００７４】
表７を参照して、熱処理１０秒で実用に十分な蛍光強度が得られる。熱処理時間を増やすに従い、蛍光強度が上がることが確認された。
【００７５】
図２および図３で説明した蛍光強度の窒素濃度の関係から、実用に十分な蛍光強度を有しない試料について、７００℃の熱処理を施した。その結果、図６（ＧａＮＡｓの場合）と図７（ＧａＩｎＮＡｓの場合）を参照して、ＧａＮＡｓ，ＧａＩｎＮＡｓともに蛍光強度か改善され、実用に十分な特性が得られた。
【００７６】
表８に、熱処理温度に対する比抵抗の変化を示す。
【００７７】
【表８】

【００７８】
測定した試料は、Ｇａ_0.9 Ｉｎ_0.1 Ｎ_0.035 Ａｓ_0.965 である。３００℃以上８００℃以下までは、到達温度を上げるに従い、比抵抗が低下する。８００℃より高く、１１００℃以下では、温度を上げるに従い、比抵抗はほぼ一定である。
【００７９】
実施例３
成長炉での熱処理に関するものである。
【００８０】
実施例１に挙げた成長方法により、実施例２に挙げた成長温度５３０℃で、ＧａＮ_0.012 Ａｓ_0.988 ，Ｇａ_0.9 Ｉｎ_0.1 Ｎ_0.035 Ａｓ_0.965 ＤＨ構造を成長した。熱処理をしない状態では、十分な蛍光特性が得られないが、ＤＨ構造を成長終了後、降温することなく熱処理を行なった。
【００８１】
図８は、素子構造を成長後、再加熱する場合の温度プロファイルを示す。
図９は、素子構造を成長後、降温することなく熱処理する場合の熱処理の時間と温度およびガス供給の変化を示す。ＤＨ構造成長終了時には、最上層のＧａＡｓ層を成長するため、水素、ＴＭＧ、ＴＢＡｓのガスを試料上に供給している。熱処理時には、ＧａＡｓ層からのＡｓ抜けを防止するために、温度を変化させる際に水素とＴＢＡｓのみを供給する。熱処理温度は、７００℃と９００℃の２種類とした。熱処理温度で１０分間保持後、室温まで冷却した。冷却時、３００℃でＴＢＡｓの供給を停止した。
【００８２】
この熱処理後、蛍光強度を測定した。結果を表９に示す。
【００８３】
【表９】

【００８４】
表９から明らかなように、実用に十分な蛍光強度が得られることがわかった。表９に、ＳＩＭＳの結果を合わせて示す。７００℃では、水素濃度の大きな低下は見られなかったが、蛍光強度は向上している。７００℃では、水素−窒素結合により赤外吸収は０であった。９００℃では、水素濃度が１桁以上低下し、蛍光強度も改善されている。
【００８５】
実施例４
実施例４は、低水素濃度の構造の熱処理に関する。実施例１に挙げた成長方法により、成長温度６００℃で、ＧａＮ_0.012 Ａｓ_0.988 ，Ｇａ_0.9 Ｉｎ_0.1 Ｎ_0.035 Ａｓ_0.965 ＤＨ構造を成長した。熱処理をしない状態でも、十分な蛍光特性が得られているが、熱処理を施し、結晶性の改善を行なった。このときの成長条件では、水素濃度は５×１０¹⁸個以下になることが、実施例１で確認されている。
【００８６】
実施例２で説明した熱処理を用い、水素雰囲気中でＤＨ構造の熱処理を行なった。結果を表１０に示す。
【００８７】
【表１０】

【００８８】
表１０から明らかなように、熱処理温度は、５００、７００、８００、９００、１１００℃の５水準とした。それぞれの温度で、蛍光強度に大きな変化は観察されないが、温度を上げるに従い、蛍光強度の半値幅が小さくなることが確認された。
【００８９】
同様の熱処理を、ＤＨ構造成長後降温することなく、引続き行なった。実施例１で示した成長方法でＤＨ構造を成長後、実施例３に示した温度、ガス供給方法により熱処理を施した。熱処理温度は、７００℃、９００℃である。結果を表１１に示す。
【００９０】
【表１１】

【００９１】
表１１から明らかなように、いずれの場合も、蛍光強度の半値幅が小さくなることが確認された。これは、熱処理により結晶性の改善が進んだためであると考えられる。これにより、より信頼性が高いレーザダイオードなどの作製が可能である。
【００９２】
【発明の効果】
以上説明したとおり、この発明によれば、発光素子の発光特性の向上、動作信頼性の向上、受光素子の受光感度の向上、動作信頼性の向上が得られるという効果を奏する。
【図面の簡単な説明】
【図１】Ｇａ_0.85Ｉｎ_0.15Ｎ_0.05Ａｓ_0.95を用いた半導体レーザと受光ダイオードの断面図である。
【図２】ＧａＮＡｓの薄膜結晶の光学特性と水素濃度の相関関係を示す図である。
【図３】ＧａＩｎＮＡｓの薄膜結晶の光学特性と水素濃度の相関関係を示す図である。
【図４】種々の窒素雰囲気中で熱処理した場合の、吸収ピークと蛍光強度の変化を測定した結果を示す図である。
【図５】（ａ）は光学特性評価用ダブルヘテロ構造の半導体装置の断面図であり、（ｂ）は電気的特性評価用単層構造の半導体装置の断面図である。
【図６】熱処理後のＧａＮＡｓの光学特性の、窒素濃度と水素濃度との関係を示す図である。
【図７】熱処理後のＧａＩｎＮＡｓの光学特性の、窒素濃度と水素濃度との関係を示す図である。
【図８】素子構造を成長後、再加熱する場合の温度プロファイルを示す図である。
【図９】素子構造を成長後、降温することなく熱処理する場合の熱処理の時間と温度およびガス供給の変化を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention generally relates to a compound semiconductor device.Manufacturing methodAnd more specifically Ga_1-xIn_xN_yAs_1-yAnd GaN_yAs_1-yCompound semiconductor device having crystal thin film as part of elementManufacturing methodAbout.
[0002]
[Prior art]
In recent years, group III-V mixed crystal semiconductors containing nitrogen as a group V element have attracted attention as a novel semiconductor material. According to this material, epitaxial growth is possible without generating misfit dislocations on Si, GaAs, InP, and GaP substrates by appropriately selecting the concentrations of nitrogen and constituent elements.
[0003]
For example, Japanese Patent Laid-Open No. 6-334168 describes an example in which a group III-V mixed crystal semiconductor is epitaxially grown on a Si substrate and monolithic with a Si electronic device is described. Japanese Patent Application Laid-Open No. 6-037355 describes an example in which GaInNAs, AlGaNAs, and GaNAs are epitaxially grown on GaAs, InP, and GaP substrates. Japanese Patent Application Laid-Open No. 9-283857 discloses an example in which a GaInNAs thin film crystal is epitaxially grown on a GaAs substrate to produce a semiconductor laser.
[0004]
A III-V mixed crystal semiconductor containing nitrogen on a GaAs substrate, for example, Ga_1-xIn_xN_yAs_1-y, GaN_yAs_1-yThe following points can be considered as advantages of producing an optical element and an electronic element by using. Until now, most of the mixed crystal semiconductors lattice-matched to the GaAs substrate have a larger band gap than GaAs. For example, AlGaAs, GaInP, etc. are mentioned. Here is a new material, Ga_1-xIn_xN_yAs_1-y, GaN_yAs_1-yHas an advantage that the band gap can be made smaller than that of GaAs.
[0005]
Ga_1-xIn_xN_yAs_1-yThen, indium composition x and nitrogen concentration y are changed to GaN._yAs_1-yThen, there is an advantage that the band gap can be continuously changed by changing the nitrogen concentration. When this material is combined with other materials to produce a multilayer structure, it is possible to produce an optical element having a wavelength longer than the emission wavelength of GaAs, which has not been realized so far. For example, Ga_xIn_1-xN_yAs_1-y, GaN_yAs_1-yBy using for the active layer, a semiconductor laser that oscillates at wavelengths of 1.3 μm and 1.55 μm used for optical fiber communication can be manufactured. In addition, a light-receiving diode that detects infrared light can be manufactured.
[0006]
In FIG._0.85In_0.15N_0.05As_0.95An example (a) of a semiconductor laser using a laser diode and an example (b) of a light receiving diode are shown. With the above composition, the semiconductor laser can oscillate laser light at 1.3 μm used for optical communication using an optical fiber.
[0007]
Ga_0.85In_0.15N_0.05As_0.95Is used in an active layer where light is excited. The light receiving diode has a p-i-n structure in which a p-type with a high carrier concentration, an n-type with a low carrier concentration, and an n-type with a high carrier concentration are stacked._0.85In_0.15N_0.05As_0.95When composed of a material, infrared light up to 1.3 μm can be detected.
[0008]
Until now, these laser diodes and light receiving diodes have been formed on InP substrates. In the case of a laser diode, InGaAsP is used for the active layer where light is excited. However, the InP substrate has a problem that it is inferior in mass productivity and price as compared with the GaAs substrate, and the laser produced on the substrate is also inferior in mass productivity and price.
[0009]
GaN_yAs_1-yAlthough not lattice-matched to GaAs, when used in the active layer of a laser diode, a diode structure can be fabricated without causing crystal defects such as misfit dislocations by sufficiently reducing the thickness. Similarly, Ga_xIn_1-xN_yAs_1-yHowever, if the composition ratio of x and y is not properly selected, misfit dislocation occurs, but the occurrence of crystal defects can be prevented by sufficiently reducing the thickness.
[0010]
[Problems to be solved by the invention]
So far, this material has been obtained by molecular beam epitaxy (MBE) using gas raw materials (Kondo et al., JJAP 35 (1996) 1273), metal organic chemical vapor deposition (OMCVD) (Sato et al., JJ 36 (1997) 2671). Although it has been grown, it has been confirmed that the optical properties deteriorate when the nitrogen concentration is increased.
[0011]
There is a method for measuring fluorescence characteristics (photoluminescence) as a method for judging whether optical characteristics are good or bad. Ga_1-xIn_xN_yAs_1-y, GaN_yAs_1-yIn general, a method of irradiating light having a wavelength of 514 nm generated by an argon laser and measuring the intensity of fluorescence emitted from the crystal is generally used.
[0012]
If there are defects or impurities in the crystal, the fluorescence is inhibited and the intensity is weakened. By measuring the intensity, the quality of the optical characteristics can be determined. In addition, the spread of the fluorescence with respect to the wavelength (generally referred to as the peak half width) correlates with the quality of the crystallinity. When the peak half width is narrow, the crystallinity is good.
[0013]
Table 1 shows GaN grown at 530 ° C. and containing no indium._xAs_1-xThe correlation (measurement room temperature) of the fluorescence intensity and nitrogen composition is shown. It can be seen that as the nitrogen concentration increases, the intensity of fluorescence suddenly decreases and the optical characteristics deteriorate. When the nitrogen concentration is high, no fluorescence is confirmed.
[0014]
[Table 1]

[0015]
Table 2 shows Ga grown at 530 ° C._0.965In_0.05N_yAs_1-yThe correlation (measurement room temperature) of the fluorescence intensity and nitrogen composition y is shown.
[0016]
[Table 2]

[0017]
As is apparent from Table 2, the same tendency as described above has been confirmed for GaInNAs.
[0018]
Table 3 shows the correlation (measurement room temperature) between the specific resistance of GaNs grown at 530 ° C. and the nitrogen composition.
[0019]
[Table 3]

[0020]
Table 4 shows the correlation (measurement room temperature) between the specific resistance of GaInNAs grown at 530 ° C. and the nitrogen composition.
[0021]
[Table 4]

[0022]
As is clear from Tables 3 and 4, GaN_xAs_1-x, GaInNAs, as the nitrogen concentration increases, the specific resistance increases and the electrical characteristics deteriorate.
[0023]
As described above, when a thin film crystal having poor optical characteristics and electrical characteristics is used as the aforementioned light emitting element, the operating characteristics and reliability of the element are remarkably deteriorated. In the case of a light receiving element, the light receiving sensitivity is low, and weak light cannot be detected. In the case of a light emitting element, the light emission intensity is weakened. In particular, a semiconductor laser cannot oscillate continuously. In either case of the light-emitting / receiving element and the electronic element, if a layer having a high resistivity exists in the multilayer film, it may not operate electrically.
[0024]
  Therefore, an object of the present invention is to provide a Ga impurity having few optical impurities sufficient for practical use and high optical characteristics and electrical characteristics._1-xIn_xN_yAs_1-y, GaN_yAs_1-yCompound semiconductor device having crystalManufacturing methodIs to provide.
[0025]
Another object of the present invention is to improve the quality of crystals by heat treatment that breaks the nitrogen-hydrogen bond and heat treatment that reduces the hydrogen concentration even when there are many hydrogen impurities. The object is to provide a manufacturing method capable of obtaining an element.
[0026]
Still another object of the present invention is to provide a production method capable of solving the problems inherent to nitride crystals by heat treatment and providing good crystals even when there are few hydrogen impurities.
[0027]
Still another object of the present invention is to provide a manufacturing method that is advantageous in saving time and energy in crystal growth by performing heat treatment subsequent to crystal growth, and enables mass production of devices. It is in.
[0028]
[Means for Solving the Problems]
  The method of manufacturing a compound semiconductor device of the present invention is a semiconductor in which infrared light used for a carrier wave of optical fiber communication is emitted, and an active layer that generates the infrared light includes a group III-V mixed crystal semiconductor containing nitrogen and arsenic. In a method for manufacturing a compound semiconductor device comprising layers, a step of preparing a GaAs semiconductor substrate, and a Ga layer on the GaAs semiconductor substrate_1-xIn_xN_yAs_1-y(0 <x ≦ 0.35, 0 <y ≦ 0.05) and / or GaN_yAs_1-yA step of forming a semiconductor layer of (0 <y ≦ 0.06) as an active layer by epitaxial growth, and after epitaxially growing the active layer, the GaAs semiconductor substrate is placed in a non-oxidizing gas atmosphere or an arsenic gas atmosphere. In a phosphorus gas atmosphere or in a vacuum,850The hydrogen concentration in the active layer is reduced to 1 cm by heat treatment at a temperature of not less than 1 ° C and not more than 1100 ° C³Per 5 × 10¹⁸And a step of making the number of pieces or less.
[0029]
  According to the above method,On a GaAs semiconductor substrateUnderstand the relationship between the heat treatment conditions and hydrogen concentration for the semiconductor layer,Ga_1-xIn_xN_yAs_1-y(0 <x ≦ 0.35, 0 <y ≦0.05) And / or GaN_yAs_1-y(0 <y ≦0 . 06) Hydrogen concentration in 1cm^ThreePer 5 × 10¹⁸PiecesThe heat treatment can be performed under the following heat treatment conditions. As a result, the hydrogen concentration of the product can be ensured to be equal to or lower than the above concentration, so that the light emission characteristics of these semiconductor layers can be improved and the electric resistance can be reduced.
[0030]
  This inventionReference compounds forAccording to the method for manufacturing a semiconductor device, first, a GaAs semiconductor substrate is prepared. On the GaAs semiconductor substrate, Ga_1-x In_x N_y As_1-y(0 <x ≦ 0.35, 0 <y ≦0.05) And / or GaN_y As_1-y (0 <y ≦0 . 06And a group III-V mixed crystal semiconductor containing nitrogen.^ThreePer 5 × 10¹⁸A semiconductor layer containing one or more hydrogen atoms is formed. The semiconductor layer has a non-oxidizing atmosphere.During ~, Arsenic gas atmosphereDuring ~, Phosphorus gas atmosphereDuring ~Or vacuumDuring ~Then, heat treatment is performed at a temperature of 500 ° C. or higher and lower than 800 ° C., thereby breaking a bond between hydrogen impurities and nitrogen in the semiconductor layer.
[0031]
  This inventionTo be helpfulAccording to the method for manufacturing a compound semiconductor device, first, a GaAs semiconductor substrate is prepared. The hydrogen concentration is 1 cm on the GaAs semiconductor substrate.^ThreePer 5 × 10¹⁸Ga or less_1-xIn_x N_y As_1-y (0 <x ≦ 0.35, 0 <y ≦0.05) And / or GaN_yAs_1-y (0 <y ≦0 . 06A semiconductor layer made of III-V mixed crystal semiconductor containing nitrogen is formed. The semiconductor layer is placed in a non-oxidizing gas atmosphere, an arsenic gas atmosphere, a phosphorus gas atmosphere, or a vacuum.During ~Then, heat treatment is performed at 500 ° C. or more and less than 1100 ° C., thereby improving crystal characteristics and optical characteristics.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
As disclosed in JP-A-9-283857, Ga is used._1-xIn_xN_yAs_1-yWhen growing a thin film crystal, As atoms are likely to be detached from the surface of the substrate and the thin film. For this reason, growth at a low temperature is necessary to prevent desorption. At such a low temperature, arsenic can be prevented from detachment and the nitrogen source can be easily adsorbed on the surface of the crystal, and there is an advantage that the nitrogen concentration can be increased. The concentration increases in proportion to the nitrogen concentration.
[0033]
In particular, in metal organic chemical vapor deposition (OMCVD), many of the organic source gas gas molecules used are composed of hydrogen atoms. Therefore, there is a problem that hydrogen is mixed into the thin film crystal. In the process of mixing hydrogen, it is conceivable that the raw material gas itself, an intermediate product during the decomposition of the raw material gas, and hydrogen atoms after decomposition from the raw material are taken into the thin film crystal. It is thought that this hydrogen behaved as an impurity and optically and electrically deteriorated. In fact, Ga_1-xIn_xN_yAs_1-yAnd GaN_yAs_1-yIn the crystal, the result of hydrogen degrading the above characteristics has not been reported so far, but there are examples investigated for other III-V mixed crystal semiconductors.
[0034]
In GaAs crystals, hydrogen has been reported to bind to doping atoms, canceling the positive or negative charge of doping atoms and becoming electrically inactive (JI Pankove, NM Johnson: Hydrogen in Semiconductors, 1996, Academic Press). In addition, an example in which optical properties deteriorate when N atoms in GaP crystals are bonded to hydrogen has been reported (Jorg Weber et al .: Mat. Res. Soc. Sym. Proc. Vol. 104, p. 325). ). The mechanism by which optical properties are degraded by hydrogen atoms remains unclear.
[0035]
From this point, the produced Ga_1-xIn_xN_yAs_1-y, GaN_yAs_1-yWhen the correlation between the optical properties of the thin film crystals and the hydrogen concentration was compared, the results of FIGS. 2 and 3 were obtained. FIG. 2 shows the case of GaNAs, and FIG._0.9In_0.1N_yAs_1-yThis is the case. Each figure shows the relationship of the hydrogen concentration to the nitrogen concentration and the respective optical characteristics. A circle in the figure indicates a sample having a fluorescence intensity sufficient for practical use, and a mark x indicates a sample having a low fluorescence intensity and insufficient for practical use. Ga grown on InP substrates currently used in laser diodes_0.25In_0.75As_0.54P_0.46The reference was one having an intensity of 1/20 or more compared to the fluorescence intensity of the crystal. The concentrations of hydrogen and nitrogen were measured by secondary ion mass spectroscopy (SIMS). In this specification, the intensity of GaInPAs for comparison is set to 20, and Ga relative to it_1-xIn_xN_yAs_1-y, GaN_yAs_1-yThe fluorescence intensity of the thin film crystal is shown. That is, if the fluorescence intensity is 1 or more, it is considered suitable for practical use.
[0036]
2 and 3, auxiliary lines A1, A2, B1, B2, C1, and C2 indicate the relationship between nitrogen concentration and hydrogen concentration when grown at 530 ° C., 550 ° C., and 600 ° C., respectively. A tendency for the hydrogen concentration to increase in proportion to the nitrogen concentration was confirmed. It was also confirmed that the hydrogen concentration decreased as the growth temperature was increased. As can be seen from these figures, the hydrogen concentration is 1 cm in order to obtain a fluorescence intensity sufficient for practical use from a thin film crystal.^Three Per 5 × 10¹⁸Must be less than
[0037]
Ga with poor fluorescence properties_1-xIn_xN_yAs_1-y, GaN_yAs_1-yRegarding the thin film crystal, the bonding state of hydrogen existing in the crystal was measured by Fourier transform infrared spectroscopy (FT-IR). As an example of this, GaN is formed on a GaAs substrate._0.012 As_0.988 An example of a sample obtained by growing a crystal by 0.5 μ is shown. The hydrogen concentration at this time is 1 cm.^Three Per 1.5 × 10¹⁹It was a piece. In addition, the measurement example of GANAs of the composition quoted here is an example in what was implemented several times.
[0038]
Wave number 2950cm^-1A clear absorption peak was confirmed at the position. This peak is observed only when nitrogen and hydrogen in the crystal are bonded to each other (when there is an N—H bond).
[0039]
When this sample was heat-treated in a nitrogen atmosphere at 500, 550, 600, 700, and 800 ° C., changes in absorption peak and fluorescence intensity were measured. The results are shown in FIG.
[0040]
As shown in FIG. 4, it can be seen that the absorption peak becomes smaller as the temperature is increased than in the case without heating. It can be seen that the heat treatment at 700 ° C. eliminates the absorption peak and provides sufficient fluorescence intensity. That is, the hydrogen concentration is 1 cm.^Three Per 5 × 10¹⁸Even in the case of larger than the number, by performing heat treatment in the temperature range of 500 to 800 ° C., the atomic bond between nitrogen and hydrogen in the crystal is broken (N—H bond is broken), and a fluorescence intensity sufficient for practical use is obtained. I understand that. The gas atmosphere is preferably a non-oxidizing atmosphere limited to hydrogen, nitrogen, argon, or helium, an arsenic gas such as arsine, a phosphorus gas such as phosphine, or a vacuum. The atmosphere gas may be a mixture of the above gases. The heat treatment time is preferably 10 seconds to 24 hours. When the uppermost layer of the structure defined in claim 1 is a semiconductor containing arsenic such as GaAs, AlGaAs, or InGaAs, an arsenic system such as arsine or tertiarybutylarsine is used to prevent arsenic from escaping from the surface due to heat treatment. It is desirable to perform heat treatment in gas. Similarly, in the case where the uppermost layer is a semiconductor containing phosphorus such as GaInP, AlGaInP, AlInP, or InGaAsP, in order to prevent phosphorus from escaping from the surface due to heat treatment, in a phosphorus-based gas such as phosphine or tertiary butylphosphine. It is desirable to perform heat treatment.
[0041]
From SIMS analysis performed after the heat treatment, the heat treatment at 500 to 800 ° C. can cut the bond between hydrogen and nitrogen, but the hydrogen concentration cannot be reduced. For this reason, high-concentration hydrogen in the crystal recombines with nitrogen, and optical characteristics and electrical characteristics are deteriorated again. Therefore, by performing heat treatment at 800 to 1100 ° C., Ga_1-xIn_xN_yAs_1-y, GaN_yAs_1-yThe bond between hydrogen and nitrogen in the thin film crystal can be broken to remove hydrogen from the crystal. Thereby, an element with high reliability can be manufactured. The gas atmosphere is preferably a non-oxidizing atmosphere limited to hydrogen, nitrogen, argon, or helium, an arsenic gas such as arsine, a phosphorus gas such as phosphine, or a vacuum. The atmosphere gas may be a mixture of the above gases. The heat treatment time is preferably 10 seconds to 24 hours.
[0042]
This heat treatment includes a method in which a multilayer structure is grown in a growth furnace, cooled to room temperature and then reheated, and a method in which the heat treatment is subsequently performed in the growth furnace after the multilayer structure is grown. A highly reliable semiconductor device can be formed efficiently and inexpensively by the method performed in the growth furnace.
[0043]
In addition to this, Ga_1-xIn_xN_yAs_1-y, GaN_yAs_1-yIs a mixed crystal semiconductor composed of elements with greatly different atomic radii, so it is very difficult to obtain crystals with a uniform composition.
[0044]
Table 5 shows the atomic radii of Group III and Group V elements.
[0045]
[Table 5]

[0046]
Referring to Table 5, atomic radii are greatly different between other Group III elements, Group V elements and nitrogen. Nitrogen and indium differ in atomic radius by about twice. When a mixed crystal semiconductor is grown with atoms having different atomic radii, distortion occurs partially and it is difficult to obtain a good crystal. This is a problem caused by the combination of materials used, and is a problem inherent to this nitride material. Hydrogen concentration is 5 × 10¹⁸Even in the case where the number is less than or equal to the number, it is possible to manufacture an element with improved crystallinity and good characteristics by heat treatment at 500 to 1100 ° C.
[0047]
According to the compound semiconductor device of the present invention, there are few hydrogen impurities sufficient for practical use, and high optical characteristics and electrical characteristics._1-xIn_xN_yAs_1-y, GaN_yAs_{1- y}Optical elements and electronic elements having crystals can be obtained. Here, the hydrogen impurity concentration sufficient for practical use is 5 × 10 5.¹⁸Or less.
[0048]
In addition, according to the present invention, even when there are many hydrogen impurities, the crystal quality is improved by heat treatment for breaking the nitrogen-hydrogen bond and heat treatment for reducing the hydrogen concentration. An element can be obtained.
[0049]
In addition, even when there are few hydrogen impurities, the heat treatment can solve the problems inherent in nitride crystals, and good crystals can be obtained.
[0050]
Furthermore, heat treatment subsequent to crystal growth is advantageous for saving time and energy for crystal growth, and enables mass production of devices.
[0051]
【Example】
Example 1
For growth, a quartz horizontal reactor was used. A semi-insulating GaAs (001) substrate was used as the substrate. Triethylgallium (TEG) and trimethylindium (TMIn) as Group III Ga and In raw materials, dimethylhydrazine (DMHy), tertiary butylarsine (TBAs) and tertiary butylphosphine as Group V N, As and P raw materials (TBP) was used. Hydrogen was used as the carrier gas. The pressure in the growth furnace was set to 76 Torr, and the growth temperature was changed at three levels of 530 ° C., 550 ° C., and 600 ° C.
[0052]
Ga lattice-matched to a GaAs (001) substrate under the following conditions:_0.9 In_0.1 N_0.035 As_0.965 Crystals could be obtained. [TBAs] / ([TEG] + [TMI]) molar supply ratio = fixed at 1.8, and at growth temperatures of 530, 550 and 600 ° C., [DMHy] / ([DMHy] + [TBAs]) molar supply ratio Are 0.98, 0.982, and 0.985, respectively, so that they are lattice-matched to the GaAs (001) substrate. Further, the nitrogen concentration was adjusted by increasing or decreasing the molar supply ratio at each growth temperature.
[0053]
Although the results are not shown in FIGS. 2, 3 and 6, 7, Ga, which is lattice-matched to the GaAs (001) substrate and has a higher In concentration._0.85In_0.15N_0.053 As_0.947 The crystal is fixed at [TBAs] / [TEG] + [TMI]) molar supply ratio = 2, and at a growth temperature of 530 and 600 ° C., the [DMHy] / ([DMHy] + [TBAs]) molar supply ratio is By setting the values to 0.984 and 0.987, respectively, GaInNAs crystals lattice-matched to the GaAs (001) substrate were obtained.
[0054]
Next, the growth method of the GaNAs crystal is as follows. The [TBAs] / [TEG] molar feed ratio is fixed at 5, and the [DMHy] / ([DMHy] + [TBAs]) molar feed ratio is varied between 0.256-0.9 according to the nitrogen concentration. It was. Three growth temperatures of 530, 550 and 600 ° C. were used.
[0055]
FIG. 5 shows an actually manufactured device structure. (A) is a figure which shows the double hetero (DH) structure for optical property evaluation, (b) is a figure which shows the single layer structure for electrical property evaluation.
[0056]
For the measurement of the optical characteristics, the double heterostructure (DH structure) in which the upper and lower sides of the GaInNAs and GaNAs thin film crystals with simplified semiconductor laser structure shown in FIG. Using this, the change in the optical characteristics was examined by measuring the intensity of fluorescence. The reason why the simplified structure is used is that when an actual laser structure as shown in FIG. 1 is used, fluorescence from GaInNAs and GaNAs crystals is scattered and absorbed by layers having different upper and lower material types, and measurement cannot be performed accurately. Because.
[0057]
The upper and lower GaAs layers were 100 nm, and the GaInNAs and GaNAs layers were 500 nm. For measurement of electrical characteristics, a GaInNAs and GaNAs thin film single crystal layer with a simplified light receiving diode shown in FIG. 5B was used. This is because, when an actual structure is used, a change in characteristics of other layers is also measured in an actual structure in which a p-type and an n-type form a junction. The measurement used a method called a Hall measurement method at room temperature. The thicknesses of the GaInNAs layer and the GaNAs layer were 500 nm.
[0058]
For the measurement of the fluorescence intensity of the prepared sample, light having a wavelength of 514 nm generated by an argon laser was irradiated, and the fluorescence intensity emitted from the crystal was evaluated by a germanium detector. For analysis of the impurity concentration by SIMS, the sample is irradiated with cesium ions and sputtered hydrogen negative ions (H^-) Was detected. The absolute concentration was calculated by comparative calibration with As ions detected at the same time. The calibration of the measurement system was carefully performed using a calibration sample in which N ions prepared separately were implanted into a GaAs thin film.
[0059]
With reference to FIG. 2 and FIG. 3 described in the embodiment, in the case of GaNAs, when growing at 600 ° C., the nitrogen concentration is 1.8 × 10 6.¹⁹~ 1.5 × 10^{twenty one}The hydrogen concentration was 2.9 × 10¹⁷~ 1.1 × 10¹⁸And low concentration. The fluorescence intensity of this sample is 2.3 to 26 when the intensity of InGaAsP is 20, and a practical fluorescence intensity is obtained at any nitrogen concentration.
[0060]
On the other hand, at 530 ° C., there is a strong correlation between the hydrogen concentration and the fluorescence intensity. Nitrogen concentration is 1.8 × 10¹⁹~ 1.0 × 10²⁰In the low range, the hydrogen concentration is 3.8 × 10¹⁷~ 2.7 × 10¹⁸And the fluorescence intensity was 1.8-14. On the other hand, the nitrogen concentration is 1.9 × 10²⁰~ 5.5 × 10²⁰In a high range, the hydrogen concentration is 5.9 × 10¹⁸~ 1.9 × 10¹⁹Thus, the fluorescence intensity is also as low as 0.09 to 0.87, which is not sufficient for practical use.
[0061]
GaInNAs to Ga_0.9 In_0.1 N_0.035 As_0.965 When the growth temperature is 530, 550, and 600 ° C., the nitrogen concentration is 7.2 × 10.²⁰And hydrogen concentration 6.2 × 10¹⁹8.9 × 10¹⁸8.2 × 10¹⁷Thus, the fluorescence intensity is 0 (below the detection limit), 0, and 2.4, respectively. Therefore, the hydrogen concentration is 5 × 10¹⁸Only in the following cases, fluorescence intensity sufficient for practical use is obtained.
[0062]
Example 2
When the growth temperature is set to 530 ° C. by the growth method described in Example 1, Ga is used._1-xIn_xN_yAs_1-y, GaN_yAs_1-yIn both cases, the hydrogen concentration in the crystal is 1 cm.^Three Per 5 × 10¹⁸More than one (see FIG. 2 and FIG. 3).
[0063]
Under these conditions, after the growth of the measurement structure described in Example 1, the film was reheated under the following conditions to measure optical characteristics and electrical characteristics.
[0064]
In this heat treatment, in order to prevent As from evaporating from the surface, a 100 nm SiN film was grown by plasma CVD. The SiN film was removed with 5% hydrofluoric acid after the heat treatment.
[0065]
The above structure was heat-treated in a hydrogen atmosphere at a pressure of 76 Torr. A quartz heating furnace was used for the heat treatment. Below, GaN_0.012 As_0.988 The example which heat-processed this sample is shown. An example in which the heat treatment temperature is 10 levels of 300, 500, 600, 650, 700, 750, 800, 850, 900, 1100 ° C. is shown. The rate of temperature increase from room temperature to the maximum temperature is 80 ° C. per minute. After reaching the heat treatment temperature, the temperature is held for 10 minutes. Then, it cools to room temperature at a temperature-fall rate of 80 degreeC per minute to room temperature.
[0066]
Table 6 shows the intensity of fluorescence with respect to the heat treatment temperature.
[0067]
[Table 6]

[0068]
Compared with the case where it is not treated, the fluorescence intensity increases as the heat treatment temperature is increased from 300 ° C. to 700 ° C. At a temperature higher than 700 ° C., the fluorescence intensity decreases, but the fluorescence intensity is higher than that in the case of no treatment.
[0069]
As described in the embodiment, FIG. 4 shows changes in hydrogen-nitrogen bonds and fluorescence intensity in this sample. It can be seen that the hydrogen-nitrogen bond is completely broken by heat treatment at 700 ° C., and fluorescence intensity sufficient for practical use can be obtained. As shown in Table 6, it can be seen that the hydrogen concentration does not decrease by heat treatment at 700 ° C., and heat treatment at 800 ° C. or higher is necessary.
[0070]
Next, two samples of GANAs and GaInNAs were heat-treated at a temperature of 700 ° C. where the fluorescence intensity was highest in the above experiment, and the heat treatment time was changed from 10 seconds to 2 hours.
[0071]
The results are shown in Table 7.
[0072]
[Table 7]

[0073]
Here, the same sample is repeatedly heat-treated, and the heat treatment time on the horizontal axis is the accumulated time at the ultimate temperature. The apparatus used was a rapid thermal annealing (RTA) apparatus capable of rapid heating. The atmosphere was nitrogen and the pressure was 760 Torr.
[0074]
Referring to Table 7, a fluorescence intensity sufficient for practical use can be obtained in 10 seconds by heat treatment. It was confirmed that the fluorescence intensity increased as the heat treatment time was increased.
[0075]
From the relationship between the fluorescence intensity and the nitrogen concentration described with reference to FIGS. 2 and 3, a sample that does not have a fluorescence intensity sufficient for practical use was subjected to heat treatment at 700 ° C. As a result, referring to FIG. 6 (in the case of GaNAs) and FIG. 7 (in the case of GaInNAs), the fluorescence intensity of both GaNAs and GaInNAs was improved, and characteristics sufficient for practical use were obtained.
[0076]
Table 8 shows the change in specific resistance with respect to the heat treatment temperature.
[0077]
[Table 8]

[0078]
The measured sample was Ga_0.9 In_0.1 N_0.035 As_0.965 It is. From 300 ° C. to 800 ° C., the specific resistance decreases as the ultimate temperature increases. Above 800 ° C. and below 1100 ° C., the specific resistance is almost constant as the temperature is increased.
[0079]
Example 3
The present invention relates to heat treatment in a growth furnace.
[0080]
According to the growth method described in Example 1, the growth temperature of 530 ° C. described in Example 2 and GaN_0.012 As_0.988 , Ga_0.9 In_0.1 N_0.035 As_0.965 DH structure was grown. In the state where the heat treatment is not performed, sufficient fluorescence characteristics cannot be obtained, but the heat treatment was performed without lowering the temperature after the growth of the DH structure.
[0081]
FIG. 8 shows a temperature profile when the device structure is grown and then reheated.
FIG. 9 shows changes in heat treatment time and temperature and gas supply when the device structure is grown and then heat treated without lowering the temperature. At the end of DH structure growth, hydrogen, TMG, and TBAs gases are supplied onto the sample to grow the uppermost GaAs layer. During the heat treatment, only hydrogen and TBAs are supplied when the temperature is changed in order to prevent As from being removed from the GaAs layer. Two types of heat treatment temperatures were used: 700 ° C. and 900 ° C. After holding at the heat treatment temperature for 10 minutes, it was cooled to room temperature. At the time of cooling, the supply of TBAs was stopped at 300 ° C.
[0082]
After this heat treatment, the fluorescence intensity was measured. The results are shown in Table 9.
[0083]
[Table 9]

[0084]
As is apparent from Table 9, it was found that a fluorescence intensity sufficient for practical use was obtained. Table 9 shows the SIMS results together. At 700 ° C., no significant decrease in hydrogen concentration was observed, but the fluorescence intensity was improved. At 700 ° C., the infrared absorption was 0 due to the hydrogen-nitrogen bond. At 900 ° C., the hydrogen concentration is reduced by one digit or more, and the fluorescence intensity is also improved.
[0085]
Example 4
Example 4 relates to a heat treatment of a structure with a low hydrogen concentration. According to the growth method described in Example 1, GaN is grown at a growth temperature of 600 ° C._0.012 As_0.988 , Ga_0.9 In_0.1 N_0.035 As_0.965 DH structure was grown. Although sufficient fluorescence characteristics were obtained even without heat treatment, crystallinity was improved by heat treatment. Under the growth conditions at this time, the hydrogen concentration is 5 × 10 5.¹⁸It has been confirmed in Example 1 that the number is less than the number.
[0086]
Using the heat treatment described in Example 2, heat treatment of the DH structure was performed in a hydrogen atmosphere. The results are shown in Table 10.
[0087]
[Table 10]

[0088]
As is clear from Table 10, the heat treatment temperature was set at five levels of 500, 700, 800, 900, and 1100 ° C. Although no significant change in fluorescence intensity was observed at each temperature, it was confirmed that the full width at half maximum of the fluorescence intensity decreased with increasing temperature.
[0089]
The same heat treatment was continued without lowering the temperature after the DH structure growth. After the DH structure was grown by the growth method shown in Example 1, heat treatment was performed by the temperature and gas supply method shown in Example 3. The heat treatment temperatures are 700 ° C. and 900 ° C. The results are shown in Table 11.
[0090]
[Table 11]

[0091]
As is apparent from Table 11, it was confirmed that in each case, the half-value width of the fluorescence intensity was small. This is presumably because crystallinity has been improved by heat treatment. This makes it possible to manufacture a laser diode or the like with higher reliability.
[0092]
【The invention's effect】
As described above, according to the present invention, it is possible to improve the light emission characteristics of the light emitting element, improve the operation reliability, improve the light receiving sensitivity of the light receiving element, and improve the operation reliability.
[Brief description of the drawings]
FIG. 1 Ga_0.85In_0.15N_0.05As_0.951 is a cross-sectional view of a semiconductor laser and a light-receiving diode using a laser diode.
FIG. 2 is a diagram showing a correlation between optical characteristics of a thin film crystal of GANAS and hydrogen concentration.
FIG. 3 is a diagram showing the correlation between the optical characteristics of a GaInNAs thin film crystal and the hydrogen concentration.
FIG. 4 is a graph showing the results of measuring changes in absorption peak and fluorescence intensity when heat treatment is performed in various nitrogen atmospheres.
5A is a cross-sectional view of a semiconductor device having a double hetero structure for optical property evaluation, and FIG. 5B is a cross-sectional view of a semiconductor device having a single layer structure for electrical property evaluation.
FIG. 6 is a diagram showing the relationship between the nitrogen concentration and the hydrogen concentration in the optical properties of GaNAs after the heat treatment.
FIG. 7 is a diagram showing the relationship between the nitrogen concentration and the hydrogen concentration in the optical properties of GaInNAs after heat treatment.
FIG. 8 is a diagram showing a temperature profile when the element structure is grown and then reheated.
FIG. 9 is a diagram showing changes in heat treatment time and temperature and gas supply when a device structure is grown and then heat treated without lowering the temperature.

Claims (4)

In a method for manufacturing a compound semiconductor device, an active layer that emits infrared light used as a carrier wave for optical fiber communication, and an active layer that generates the infrared light includes a semiconductor layer in which a group III-V mixed crystal semiconductor contains nitrogen and arsenic.
Preparing a GaAs semiconductor substrate;
On the GaAs semiconductor substrate, Ga _1-x In _x N _y As _1-y (0 <x ≦ 0.35, 0 <y ≦ 0.05) and / or GaN _y As _1-y (0 <y ≦ 0.06) forming a semiconductor layer as an active layer by epitaxial growth;
After epitaxially growing the active layer, the GaAs semiconductor substrate is heat-treated at 850 ° C. or higher and 1100 ° C. or lower in a non-oxidizing gas atmosphere, an arsenic gas atmosphere, a phosphorus gas atmosphere, or a vacuum, And a step of setting the hydrogen concentration in the active layer to 5 × 10 ¹⁸ or less per 1 cm ³ .   The method of manufacturing a compound semiconductor device according to claim 1, wherein secondary ion mass spectroscopy is used as a method for measuring the hydrogen concentration in the semiconductor layer.   The method for manufacturing a compound semiconductor device according to claim 1, wherein an absorption spectrum obtained by Fourier transform infrared spectroscopy is used as a method for measuring the hydrogen concentration in the semiconductor layer.   The method of manufacturing a compound semiconductor device according to claim 1, wherein the heat treatment is performed immediately after the semiconductor layer is epitaxially grown on the GaAs semiconductor substrate without lowering the temperature. .

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