AlGaN/GaN多重量子井戸におけるサブバンド間遷移  [in Japanese] Intersuband transition in AlGaN/GaN multiple quantum wells  [in Japanese]

窒化物半導体中多重量子井戸には大きな格子歪みが存在し、これが結晶性、バンド間発光特性、そしてサブバンド間遷移(ISBT)に、どのような影響を及ぼすか考察を行った。井戸層中には障壁層厚と井戸層厚の比で決まる、歪みに起因した内部電界が発生し、バンド間発光波長とISBT波長とは1対1には対応しない。また障壁が厚い場合には歪みエネルギーが増大し、格子が部分的に緩和した状態になる。障壁層厚を薄めに設定することで、障壁のAl組成が65%で井戸数が200ものMQW構造や、Al組成が85%と非常に高い障壁のMQW構造を作製、いずれもサブバンド間吸収の観測に成功した。

There is large lattice strain in AlGaN/GaN multiple quantum wells (MQWs). We investigate how the strain affects the crystalline quality, interband luminescence properties and intersubband transition (ISBT). The lattice strain produces the internal field, of which magnitude is determined by the ratio of the well and the barrier. Due to the field, ISBT wavelength does not correspond to the interband luminescence wavelength. When the barriers are thick, the strain energy increases and the lattice is partly relaxed. By setting the barrires thinner, we grew MQWs which consist of as many as 200 wells and barriers with Al content of 0.65 and we grew MQWs with Al content of as high as 0.85. We successfully observed the intersubband absorptions for both samples.