Thermal budget increased alloy disorder scattering of 2DEG in III-N heterostructures

Abstract

High-temperature processing steps are frequently used in manufacture of AlGaN/(AlN/)GaN high electron mobility transistors (HEMTs). The thermal budgets drive Al diffusion into the GaN channel, increase alloy disorder scattering (ADS) of the two-dimensional-electron-gas (2DEG), and degrade the 2DEG mobility. By correlating the ADS to device thermal budget, we propose an analytical model to calculate the ADS limited mobility as a function of Al diffusion lengths (L-D,L-Al) in AlGaN/(AlN/)GaN HEMTs. The simulation indicates that the ADS is a significant mobility degradation mechanism whose scattering rate increases with the 2DEG density and the L-D,L-Al. The findings explain the generally observed trends in the literature that the 2DEG mobility and sheet resistances of GaN heterostructures degrade with increased thermal budgets, especially after >900 degrees C processing.