Al Ga As ∕ Ga As high-electron mobility transistor with In0.1Ga0.9As∕In0.22Ga0.78As∕In0.1Ga0.9As channel grown by metal-organic chemical vapor deposition

Abstract

A composite-channel high-electron mobility transistor (HEMT) on GaAs substrate is designed and fabricated, using the following methodology to improve device performance: (1) an AlGaAs buffer layer, (2) an AlGaAs∕GaAs superlattice layer, and (3) an In0.1Ga0.9As∕In0.22Ga0.78As∕In0.1Ga0.9As composite channel. For comparison, a control HEMT without the composite channel is fabricated in parallel (whose channel comprises only a 125-Å-thick In0.22Ga0.78As layer). These two devices are grown by metal-organic chemical vapor deposition. The peak extrinsic transconductance (gm,ext) of the control HEMT with a gate length of 1μm is 160mS∕mm, while the peak gm,ext of the composite-channel HEMT of the identical gate length is measured to be 186mS∕mm. The on-state breakdown voltage of the composite-channel HEMT is as great as 9.7V, which represents an improvement of 1.4V over the control HEMT. The control HEMT exhibits a current gain cutoff frequency (fT) of 12.5GHz and a maximum frequency of oscillation (fmax) of 31.5GHz, while the composite-channel HEMT exhibits an fT of 16.9GHz and an fmax of 37.4GHz. Experimental data reveal that the composite-channel structure provides improved gate-to-source voltage swing, improved saturation current density, enhanced fT, enhanced fmax, and enhanced breakdown voltage without compromising electron mobility. The composite-channel HEMT is thus far superior to the control HEMT and is highly promising for use in high-frequency applications.