GaAs MOSFETs - a viable single supply III-V RF technology solution?

Abstract

This paper summarises the current state of the art in GaAs MOSFETs, and argues that the 4 decade search for a device quality compound semiconductor oxide is over. Under suitable growth conditions, a GaO/GaGdO high-k (~20) gate dielectric has been shown to have a mid-gap density of states of 2.5 x 1011 cm-2 eV-1 [1], and vitally, an unpinned oxide-semiconductor interface [2]. With a scalable vertical architecture, enhancement mode implant-free III-V MOSFETs [3] with an In0.25GaAs channel layer, have yielded electron transport metrics comp25GaAs channel layer, have yielded electron transport metrics comparable to GaAs pHEMTs of similar materials compositions-namely mobility of above 5000 cm2/Vs for carrier concentration above 2 x 1012 cm-2 [4]. From these material structures, 1 μm gate length GaAs MOSFETs with a 10 nm gate oxide have been realised with threshold voltage of +0.26 V, saturation drive current, Id,sat = 407 mA/mm,arable to GaAs pHEMTs of similar materials compositions-namely mobility of above 5000 cm2/Vs for carrier concentration above 2 x 1012 cm-2 [4]. From these material structures, 1 μm gate length GaAs MOSFETs with a 10 nm gate oxide have been realised with threshold voltage of +0.26 V, saturation drive current, Id,sat = 407 mA/mm, maximum extrinsic transconductance, gm = 477 mS/mm, output conductance, gd = 11 mS/mm , gate leakage current, Ig = 60 pA for gate voltages up to + 2.0 V, subthreshold swing, S = 102 mV/dec, on resistance, Ron = 1.920 Ωmm, and Ion/Ioff ratio = 6.3 x 104 [4]. A gate voltage swing of +2 V can easily be accommodated with these devices, making them attractive as a single supply III-V technology. Enhancement mode operation can be sustained to 300 nm with this oxide thickness, with peak intrinsic transconductance increasing to 600 mS/mm, indicative of the on-set of non-equilibrium transport effects, similar to short gate length pHEMTs [5]. Initial RF data from 0.8 μm gate length III-V MOSFETs with a threshold voltage of +0.4 V, resulted in fT and fmax of 14 GHz and 40 GHz respectively. (5 pages)