Experimental evidence of temperature dependent effective mass in AlGaN/GaN heterostructures observed via THz spectroscopy of 2D plasmons

Abstract

Temperature-dependent effective mass in AlGaN/GaN heterostructures was experimentally observed via THz time domain spectroscopy of 2D plasmons in the range of 80–300 K. Grating couplers with different periods and filling factors were developed in order to monitor the behavior of plasma resonances in transmission spectra in the frequency range of 0.5–3.5 THz. For the grating with a 50% filling factor, the fundamental modes were excited and observed at temperatures below 225 K. The change of the filling factor to 80% led to the excitation of the fundamental and second order plasma harmonics observable up to 300 K and 220 K, respectively. Moreover, with an increase in temperature, the 2D plasmons experienced the red-shift in transmission power and phase spectra of all samples. This phenomenon was explained by the renormalization of effective mass, which started distinctly to deviate at 134 K temperature and at 295 K increased up to 55% of its nominal value. The THz spectroscopy of 2D plasmons further confirms a temperature-dependent effective mass in AlGaN/GaN heterostructures as reported previously in optical Hall effect studies.