Improved Recessed-Gate Structure for Sub-0.1-µm-Gate InP-Based High Electron Mobility Transistors

An improved recessed-gate structure for high-performance short-gate InP-based InAlAs/InGaAs high electron mobility transistors (HEMTs) is presented. The effective gate length of the HEMTs is found to be related to the electron density in the side-etched region between the gate and the ohmic capped region. The higher electron density in the side-etched region is efficiently suppresses the effective gate length. A new gate recess process, which consists of a sequence of wet-chemical etching and Ar-plasma etching, enables us to reduce the effective gate length. The new recessed-gate structure successfully provides improved performance with high uniformity. A cutoff frequency of 300 GHz is achieved even with 0.07-µm-gate HEMTs.