Application of the Ag-Based Ohmic Contact to the Realization of Thermally-Stable InAlAs/InGaAs/InP High Electron Mobility Transistors

Auger electron spectroscopy analysis of Ag-based Ge/Ag/Ni ohmic contacts on InAlAs/InGaAs/InP revealed that the in-diffusion of the Ag down to the semiconductor layers was necessary for the formation of excellent ohmic contact. Atomic force microscopy characterization of the surface morphology showed that the root mean square roughness of the ohmic contact after annealing was as small as 3.0 nm. High electron mobility transistors with a gate length of 0.2 µm fabricated utilizing Ag-based ohmic contact showed excellent DC and RF characteristics including: g_m,max of 835 mS/mm, I_D,max of 813 mA/mm, f_T of 156 GHz, and f_max of 245 GHz. Due to the stable property of the Ag-based source and drain ohmic contacts, these devices were shown to be thermally stable through preliminary thermal storage tests at 215 °C.