窒化物半導体トンネル接合の作製

摘要

本報告では、高抵抗p型窒化物半導体に制限されない電流注入を目指して、窒化物半導体を用いたトンネル接合の検討を行った。はじめに、窒化物半導体トンネル接合逆方向における電流電圧特性を計算した。100A/cm~2以上の十分な電流密度を得るためには、トンネル接合障壁幅を3nm以下にする必要があり、このために不純物濃度を5×10~(20)cm~(-3)以上にする必要があることがわかった。続いて、MOWE法によりトンネル接合を介して電流注入するLEDを成長した。上記高い不純物濃度実現のためにトンネル接合形成時のMg/Ga比を増やすと、表面が荒れることがわかり、膜厚を調整することで比較的良好な表面状態が得られることがわかった。このトンネル接合を用いた電流注入によるLEDからは比較的均一な発光が得られ、20mA注入時の駆動電圧は12.5Vと高い値であった。%We have investigated nitride semiconductor-based tunnel junctions for a novel current injection, not restricted with the high resistivity of the p-type GaN layers. First, the reverse current-voltage characteristics of the nitride semiconductor tunnel junctions were calculated. It seems necessary to obtain less than 3nm tunnel barriers for enough current injections (more than 100A/cm~2), which also requires at least 5 × 10~(20)cm~(-3) impurities in the tunnel junctions. Subsequently, we fabricated LED structures injected the current through the tunnel junctions by MOVPE. We found that the sample surfaces got rough as Mg/Ga ratio was increased during the growth of the tunnel junctions to achieve the high impurity concentrations mentioned above. At the same time, relatively smooth surfaces were obtained by adjusting the thicknesses of the highly doped layers. A relatively uniform light emission was then obtained from the LED with the tunnel junction, showing high driving voltage, 12V at 20mA injection.