Optical performance of two dimensional electron gas and gan:С buffer layers in algan/aln/gan heterostructures on sic substrate

Abstract

Terahertz time‐domain spectroscopy and Fourier‐transform infrared spectroscopy were developed as the method for the investigation of high‐frequency characteristics of two‐dimensional electron gas and GaN:С buffer layers in AlGaN/AlN/GaN heterostructures grown on a semi‐insulating SiC substrate. The reflectance and transmittance spectra of the selected heterostructure layers were studied after the top layers were removed by a reactive ion etching. Results were numerically analyzed using the transfer matrix method taking into account the high‐frequency electron conductivity via a Drude model and complex dielectric permittivity of each epitaxial layer via a one‐phonon‐resonance approximation. Good agreement between the experiment and theory was achieved revealing the temperature dependent electron effective mass in AlGaN/AlN/GaN high electron mobility transistor structures and the small damping factors of optical phonons due to high crystal quality of the epitaxial layers fabricated on the SiC substrate.