Optical and theoretical study of strong electron coupling in double GaN/AlN quantum wells

The electronic confinement in GaN quantum wells coupled by an ultra-thin AlN barrier is investigated both experimentally and theoretically. The strong coupling between the wells is evidenced by the observation of two pronounced intersubband absorptions peaked at around 0.6 and 0.95 eV for 2 monolayer thick AlN coupling barrier. In agreement with calculations, these absorptions are attributed respectively to the transitions between the ground states of the two coupled wells and between the ground state and the excited state delocalized between the two wells. The experimental results provide clear evidence that the potential drop at the GaN/AIN interfaces is not abrupt, but spread over 1 monolayer.