Experimental and computational study of the high-temperature 2DEG mobility in AlGaN/GaN heterostructures

Abstract

AlGaN/GaN heterostructures are widely used in high power RF applications due to the high two-dimensional electron gas (2DEG) mobility. The wide bandgap of GaN makes it attractive for high-temperature electronics applications. In this work, we report both experimental and computational studies of the AlGaN/GaN 2DEG mobilities at elevated temperatures. AlGaN/GaN heterostructures were grown by MOCVD. After forming Ohmic contacts, the 2DEG mobility and density were measured using van der Pauw structures up to 500 °C. The 2DEG mobility drops to <20% of the room temperature values. To understand the mobility limiting mechanisms, a comprehensive ab initio-based electron–phonon interactions calculations were carried out to accurately quantify the electron–phonon scattering rates. Contributions from polar optical phonons, piezoelectric scattering by acoustic phonons including the quadrupole corrections, and non-polar deformation potential scattering were included. In addition, interface roughness and remote alloy disorder scattering were also included. First, the Poisson's and Schrödinger's equations are solved self-consistently to get the 2DEG wavefunctions. Then, using ab initio methods, the electronic band structure, phonon modes, and the electron–phonon interaction matrix elements were calculated. For all the scattering mechanisms, a temperature-dependent static screening has been used. Finally, the Boltzmann Transport Equation is solved using Rode's iterative method to get the low-field mobility. The calculated results show a good fit with experiments over the whole temperature range. Even though all the phonon scatterings increase with temperature, the polar optical phonon scattering dominates at higher temperatures due to increased Bose–Einstein occupancy and reduced screening ultimately limiting the mobility.