Calculation of Near-Infrared Intersubband Absorption Spectra in GaN/AlN Quantum Wells

Intersubband transitions in GaN multiple quantum wells (MQW) are expected to be applicable to 1-Tb/s all-optical switches. The near-infrared (1.33–2.15 µm) intersubband absorption spectra of GaN/AlN MQW samples have been theoretically investigated. The measured spectra have been well explained by a model in which zero-voltage drop across one quantum well period and 0.5- to 0.75-nm-thick interface graded layers were assumed. The effective electric field in the well was estimated to be greater than 5 MV/cm. For thick wells, absorption spectra are sensitive to the electric field, and hence to the strain, barrier thickness, and doping level. In thin wells, the effect of the electric field is negligible, but the quality of the interface affects the spectra. The calculation model has been applied to the design of coupled quantum wells (CQW), where faster optical response is expected. Higher-order intersubband absorption at wavelengths of less than 1 µm is also expected to be enhanced in CQWs.