Theoretical analysis of modulation doping effects on intersubband transition properties of semipolar AlGaN/GaN quantum well

The effects of modulation doping on the intersubband transition (ISBT) properties of semipolar AlGaN/GaN quantum well (QW) are investigated theoretically using QW doping, barrier doping, and barrier δ-doping schemes at 150 K. Important ISBT parameters such as intersubband transition energies, dipole matrix elements, and absorption spectra are calculated for QW structures on both semipolar (20 2 - 1) (i.e., with weak polarization) and (10 1 - 3) (i.e., with strong polarization) planes. For (20 2 - 1) QW with weak polarization, it is found that high doping concentrations can cause a significant band bowing to the QW structures, which reduce the absorption coefficients and wavelengths. This band bowing effect will become stronger when doping layers are closer to the QW. For (10 1 - 3) QW with a strong polarization, however, a weak band bowing effect is observed due to the large polarization and large band tilting of (10 1 - 3) QW. The study shows that modulation doping is a promising method to modify the ISBT properties of semipolar AlGaN/GaN QW to achieve an improved performance such as longer ISBT wavelength (e.g., >20 μm).