Effect of polarization on intersubband transition in AlGaN/GaN multiple quantum wells

Intersubband transitions (ISBT) of AlGaN/GaN multiple quantum wells (MQWs) with wavelength towards atmospheric window (3–5 μm) have been investigated. A Ga-excess epitaxial method is used in the molecular beam epitaxy leading to ultra-sharp interface and negligible elements inter-diffusion. The absorption peak wavelength of the ISBT was successfully tuned in the range of 3–4 μm by modifying the GaN well thickness from 2.8 to 5.5 nm. It was further found that the polarization charge density of the AlGaN/GaN MQWs was about −0.034 C/m2 which gave rise to blueshift of the ISBT wavelength and thus partially compensated its redshift with increasing well thickness.