Effects of Crystal Defects in GaN on Electron Devices

GaN 系半導体材料は結晶成長，プロセス技術に大きな進展を成し遂げ，光デバイスだけでなく，電子デバイス応用としても高出力パワーアンプ，パワースイッチングの分野で実用化を迎える段階に研究開発が進展した．本稿では著者がデバイス開発の過程で観測した結晶欠陥起因の現象として，転位と電気的特性の相関，p-GaN 電極のショットキー障壁高さ及びメモリー効果，熱処理による2 次元電子ガス濃度の変動，及び結晶の平坦性が電子速度に与える影響の4 つの例を取り上げ，そのメカニズムを解明した結果について解説を行う．AlGaN/GaN high-electron-mobility transistors have been intensively studied as high-temperature high-power high-frequency electron devices. In this article， four topics， which related to the effects of crystal quality on device characteristics are reported. （i） Correlation between current－voltage （I－V） characteristics and dislocations was evaluated by using sub-micron diameter n-GaN Schottky contacts. The diodes showed that neither mixed nor edge dislocation affected I－V characteristics. （ii） Evaluation of Schottky barrier height was conducted for low-Mg-doped p-GaN. Large Schottky barrier height of 2.4 eV was obtained and memory effects were observed. （iii） Thermal stability of 2 dimensional electron gas was evaluated. The carrier concentration was sensitive to AlGaN crystal quality. （iv） The electron velocity in short-gate HEMTs with different crystal quality was evaluated. The measured velocities were virtually the same for all devices