Temperature-Dependent DC Characteristics of GaN/InAlN/GaN HEMTs: GaN Cap Layer Thickness and Doping Effects

This study investigates the effects of GaN capping layer thickness and heavy n-type doping on GaN/InAlN/GaN HEMTs performance. The focus is on the thermal influence on the 2D electron gas (2-DEG) density ns in these heterostructures. The analysis considers both spontaneous and piezoelectric polarization at the InAlN/GaN and GaN/InAlN interfaces. Simulation results show that n+-doped GaN caps increase the 2-DEG sheet carrier density (SCD) relative to undoped layers. However, the GaN cap layer (GCL) also reduces the 2-DEG density, resulting in lower drain current. Furthermore, the drain current degrades with temperature, decreasing significantly as the temperature rises from 300 to 425 K. Thermal and self-heating (SH) effects have been found to drastically diminish drain-source current. At high drain voltages, these thermal effects can cause a region of negative differential resistance, especially evident in the GaN/InAlN/GaN structure. With a drain bias of Vds = 10 V, the drain current Ids decreases from approximately 728 mA at 300 K to 663 mA at 425 K, highlighting the significant role of thermal effects on HEMT performance.