Systematic study of near-infrared intersubband absorption of polar and semipolar GaN/AlN quantum wells

We report on the observation of intersubband absorption in GaN/AlN quantum well superlattices grown on $(112¯2)$-oriented GaN. The absorption is tuned in the $1.5–4.5 μm$ wavelength range by adjusting the well thickness. The semipolar samples are compared with polar samples with identical well thickness grown during the same run. The intersubband absorption of semipolar samples shows a significant red shift with respect to the polar ones due to the reduction of the internal electric field in the quantum wells. The experimental results are compared with simulations and confirm the reduction of the polarization discontinuity along the growth axis in the semipolar case. The absorption spectral shape depends on the sample growth direction: for polar quantum wells the intersubband spectrum is a sum of Lorentzian resonances, whereas a Gaussian shape is observed in the semipolar case. This dissimilarity is explained by different carrier localization in these two cases.