Gate-Recess Technology for InAs/AlSb HEMTs

The gate-recess technology for Si delta-doped InAs/AlSb high-electron-mobility transistors (HEMTs) has been investigated by combining atomic force microscopy (AFM) inspection of the gate-recess versus time with electrical device characterization. Deposition of the gate metal on the In 0.5 Al 0.5 As protection layer or on the underlying AlSb Schottky layer resulted in devices suffering from high gate-leakage current. Superior dc and high frequency device performance were obtained for HEMTs with an insulating layer between the gate and the Schottky layer resulting in a reduction of the gate leakage current I G by more than two orders of magnitude at a drain-to-source voltage VDS of 0.1 V. The existence of this intermediate insulating layer was evident from the electrical measurements. AFM measurements suggested that the insulating layer was due to a native oxidation of the AlSb Schottky layer. The insulated-gate HEMT with a gate length of 225 nm exhibited a maximum drain current I D higher than 500 mA/mm with good pinchoff characteristics, a dc transconductance g m of 1300 mS/mm, and extrinsic values for cutoff frequency f T and maximum frequency of oscillation f max of 160 and 120 GHz, respectively.