Effects of Gate-Recess Structure on High-Frequency Characteristics of 0.1 μm Metamorphic HEMTs

Abstract

We investigate effects of the gate-recess structure on the high-frequency characteristics of the depletion-mode metamorphic high electron mobility transistors (HEMTs). We characterize the dc and radio frequency performances of two different gate-recess structures and perform a comparative study using the hydrodynamic device model simulation and small-signal parameter analysis. The narrow gate-recess structure shows significantly higher dc performances than the wide gate-recess structure, and this phenomenon is due to the presence of the negatively charged surface states on the Schottky barrier layer surface in the wide gate-recess structure. Despite the superior dc characteristics, the narrow gate-recess structure shows more degraded maximum frequency of oscillation of than that of the wide gate-recess structure and almost the same cutoff frequency of . The degraded of the narrow gate-recess structure is attributed to a higher gate-to-drain capacitance . The significant increase of is caused by the reduction of effective gate-to-drain spacing due to the nonlinear electric potential distribution in the gate-to-drain region.