Experimental and computational study of the high temperature 2DEGmobility in AlGaN/GaN heterostructures

AlGaN/GaN hetero-structures are widely used in high power RF applications due to the high two-dimensional electrongas (2DEG) mobility. The wide bandgap of GaN makes it attractive for high temperature electronics applications. Inthis work, we report both experimental and computational study of the AlGaN/GaN 2DEG mobilities at elevated temperatures.AlGaN/GaN heterostructures were grown by MOCVD. After forming ohmic contacts, the 2DEG mobilityand density were measured using van der Pauw structures up to 500 {degree sign}C. The 2DEG mobility drops to < 20% of theroom temperature values. To understand the mobility limiting mechanisms, a comprehensive ab-initio-based electronphonon interactions calculations were carried out to accurately quantify the electron-phonon scattering rates. Contributionsfrom 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 disorderscattering were also included. First, the Poisson's and Schrödinger's equations are solved self-consistently to get the2DEG wavefunctions. Then, using ab-initio methods, the electronic band structure, phonon modes, and the electronphononinteraction matrix elements were calculated. For all the scattering mechanisms, a temperature-dependent staticscreening has been used. Finally, the Boltzmann Transport Equation is solved using Rode's iterative method to get thelow-field mobility. The calculated results show a good fit with experiments over the whole temperature range. Eventhough all the phonon scatterings increase with temperature, the polar optical phonon scattering dominates at highertemperatures due to increased Bose-Einstein occupancy and reduced screening ultimately limiting the mobility.