Resonant tunnelling and intersubband absorption in AlN - GaN superlattices

We report on intersubband absorption and photovoltage measurements on regular GaN/AlN-based superlattice structures at 1.55 <i>µ</i>m. For high barriers, the photovoltage peaks at a higher energy than the absorbance spectrum due to the decrease of the tunnelling probability. The observed photovoltage is thus the macroscopic manifestation that the 2-dimensional electron gas at the top of the superlattice gets depleted by a vertical transport of electrons.