成果報告書詳細
管理番号20110000001478
タイトル*平成22年度中間年報 ナノエレクトロニクス半導体新材料・新構造技術開発~窒化物半導体・エピタキシャル成長技術の開発 ナノエレクトロニクス半導体新材料・新構造技術開発ー窒化物系化合物半導体基板・エピタキシャル成長技術の開発
公開日2011/12/13
報告書年度2010 - 2010
委託先名財団法人金属系材料研究開発センター 国立大学法人大阪大学 国立大学法人名古屋大学 国立大学法人福井大学 昭和電工株式会社 住友電気工業株式会社 サンケン電気株式会社 古河機械金属株式会社
プロジェクト番号P07030
部署名電子・材料・ナノテクノロジー部
和文要約和文要約等以下本編抜粋:1.研究開発の内容及び成果等
1)「高品質大口径単結晶基板の開発」
(1)窒化物単結晶成長における基礎技術の検討(大阪大学、JRCM)
【1】 溶液状態制御技術の開発
・1軸揺動機構および回転攪拌機構において、様々な攪拌パターンの効果を検証した。攪拌の効果の検証実験として、点状の種結晶上への結晶育成を行った。各攪拌パターンにおける収率の変化、および得られた結晶の写真をそれぞれ図1、図2に示す。攪拌無しの育成では、骸晶結晶が成長し、坩堝壁上に大量の多結晶が発生した。1軸揺動の育成では傾斜角をおよそ10°とし、揺動周期を1.5、3.0、7.0 rpm
とした。その結果、1.5 rpmで多結晶が大幅に減少し、3.0 rpmで多結晶の発生はなくなった。また、揺動周期が増すにつれて収率が上昇し、成長した結晶の骸晶化が改善した。7.0 rpmで骸晶化が見られなくなり、収率が最も高くなった。回転攪拌では回転周期を30 rpm一定とし、常に一定方向に回転し、一定周期ごとに停止する正転パターン、一定周期ごとの停止に加え、回転方向を反転させる反転パターンを行った。育成の結果、正転パターンでは攪拌なしに比べ、多結晶発生が大幅に減少し、収率が上昇したが結晶は骸晶化した。反転パターンでは多結晶の発生はなく、正転パターンと比較し高い収率が得られた。また結晶の骸晶化も大幅に改善した。以上の結果より、1軸揺動の場合では揺動周期を上げること、回転攪拌の場合は反転を行うことにより、窒素の溶解量が増加、かつ溶液中の窒素濃度が均一化されると考えられ、多結晶の発生なく骸晶化のない結晶を高い収率で得る上で有効であるが分かった。
英文要約Title: Development of Nitride-based Semiconductor Single Crystal Substrate and Epitaxial Growth Technology (FY2007~2011) FY2010 Annual Report
■ [Development of High-Quality Large-Size Substrates]
・Studies of the solution stirring technique of the Na-flux LPE method have revealed that short-period shaking of crucibles effectively increases the crystal yield for the see-saw motion. This increase is believed to be due to the high solubility and uniform distribution of nitrogen in the Ga~Na mixed solution. It was also found that the rotational pattern of the crucible, such as changes of direction, is important for rotational motion.
・The addition of Ca or Ba to the Ga~Na mixed solution resulted in improvements in the surface roughness of nonpolar LPE-GaN crystals grown on a-plane HVPE-GaN templates and m-plane free-standing substrates sliced from a c-plane HVPE-GaN. Full width at half maximum for the X-ray diffraction profiles of a-plane LPE-GaN crystals were 65 arcseconds and 47 arcseconds for the Ca and Ba systems, respectively.
・A free-standing 2.6-inch-φ GaN substrate was successfully realized using the Na-flux LPE method with a free-standing c-plane HVPE-GaN substrate as the starting material.
No pits appeared to have propagated from the seed substrate and no cracks were observed within the LPE-GaN substrate.
・We also succeeded in achieving the growth of conductive substrates having specific resistance values below 0.01 Ω~cm by high Ge doping. Furthermore, it was also revealed that Zn-doped substrates had specific resistance values of 3 ~ 106 Ω~cm at RT and exhibited temperature dependence with an activation energy of 0.57 eV.
■ [Development of High-Quality Epitaxial Films on Large-Size Wafers]
・High-In-content Ga0.25In 0.75N epitaxial films were successfully grown on a c-plane 4-inch sapphire substrate using a high-pressure MOVPE system. It was confirmed that the film had good uniformity within ±10% for both thickness and In content.
・High-impurity doping for Ga0.25In0.75N epitaxial films was demonstrated. It was confirmed that for Si-doping, the average dopant concentration was 1.5 ~ 1019 cm~3 and the variation in the concentration was within ±5%, whereas for Mg-doping, the average dopant concentration was 1.5 ~ 1020 cm~3 and the variation in the concentration was within ±5%.
・A high-Al-content Ga0.4Al0.6N epitaxial film was successfully grown on a c-plane 4-inch sapphire substrate. The uniformity of the Al content within a wafer was ±1.3% while that of the film thickness was ±3.7%.
・Si doping for Ga0.25In0.75N epitaxial films was demonstrated that was grown on a m-plane AlN substrate. It was confirmed that the average dopant concentration was 8 ~ 018 cm~3.
■ [Fabrication and Characterization of Electron Devices on Nitride Semiconductor Substrates]
・An AlGaN/GaN-FET array was fabricated on a free-standing 3-cm-diameter Na-flux GaN substrate with a dislocation density of the order of 104~105 cm~2. AlGaN/GaN-FETs with 3-μm-length gates exhibited good pinch-off characteristics and low leakage current.
・AlGaN-channel circular-shaped HFETs (Al0.26Ga0.74N/Al0.5Ga0.5N) with 6-μm-length gates and 10 μm gate~drain distance were fabricated on a free-standing AlN substrate that had a maximum drain current of 135 mA/mm and a breakdown voltage of 1400 V.
・It was also found that the degradation of drain current over the temperature ranging from room temperature to 300 °C was 20% for AlGaN-channel HFET (Al0.51Ga0.49N/Al0.86Ga0.14) devices, which was much smaller than that for GaN-channel HFET devices (80%).
・The origins of the leakage current of PN diodes, which were fabricated on a free-standing Na-flux GaN substrate, were investigated. There was no relationship between etch pits and the luminescence that originated from the leakage current. Most etch pits were either edge dislocations or mixed dislocations. No screw dislocations were observed by TEM analysis.
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