Bias-Dependent Microwave Characteristics of Atomic Planar-Doped AIGaAs/InGaAs/GaAs Double Heterojunction MODFET´s (Short Paper)

Double heterojunction AIGaAs/InGaAs/GaAs modulation-doped field effect transistors (MODFET´s) using lattice-strained AIGaAs/InGaAs/GaAs layer structure have been fabricated and evaluated at microwave frequencies for various bias conditions. MODFET´s with a 1-µm gate length show a room-temperature peak extrinsic dc transconductance (g_m) of 400 mS/mm with a full channel current of 610 mA/mm. For 0.3-µm-gate MODFET´s an extrinsic dc g_m of 505 mS/mm and a full channel current of 720 mAmm were obtained. Devices having a 1-µm gate length show a maximum available gain cutoff frequency (f_max) of 85 GHz and a current-gain cutoff frequency (f_T) of 22 GHz from S-parameter measurements. The 0.3-µm devices show an f_T of 45 GHz and an f_max of 120 GHz. Bias-dependent equivalent circuit models are also discussed.