Origin of the blueshift in the infrared absorbance of intersubband transitions in image N/GaN multiple quantum wells

A self-consistent calculation of the subband energy levels of n-doped quantum wells is studied. A comparison is made between theoretical results and experimental data. In order to account for the deviations between them, the ground-state electron–electron exchange interactions, the ground-state direct Coulomb interactions, the depolarization effect, and the exciton-like effect are considered in the simulations. The agreement between theory and experiment is greatly improved when all these aspects are taken into account. The ground-to-excited-state energy difference increases by 8 meV from its self-consistent value if one considers the depolarization effect and the exciton-like effect only. It appears that the electron–electron exchange interactions account for most of the observed residual blueshift for the infrared intersubband absorbance in AlxGa1-xAlxGa1-xN/GaN multiple quantum wells. It seems that electrons on the surface of the k-space Fermi gas make the main contribution to the electron–electron exchange interactions, while for electrons further inside the Fermi gas it is difficult to exchange their positions.