Midinfrared intersubband absorption on AlGaN/GaN-based high-electron-mobility transistors

Intersubband absorption measurements on two nominally undoped AlGaN/GaN-based high-electron-mobility transistors with different Al compositions in the barrier layer are presented. The first transistor with a barrier consisting of Al_0.6Ga_0.4N showed an absorption peak at 247 meV (1973 cm^–1) with a full width at half maximum (FWHM) of 126 meV, while the second device utilizing an Al_0.8Ga_0.2N barrier had its peak at 306 meV (2447 cm^–1) with a FWHM of 86 meV. Self-consistently computed potentials and intersubband transition energies showed good agreement with the experimental findings, and therefore confirmed previously published values for the internal piezoelectric field in such structures.