Comparison of single and double barrier pseudomorphic doped-channel GaInP/GaInAs/GaAs HFET's: performance and isolation properties

Doped-channel GaInP/GaInAs/GaAs pseudomorphic heterostructure field-effect transistors (HFETs) were fabricated both with and without a GaInP barrier layer under the GaInAs channel. Two sets of alloy compositions were investigated: Ga/sub 0.85/In/sub 0.15/As channels with Ga/sub 0.51/In/sub 0.49/P barriers, and Ga/sub 0.70/In/sub 0.30/As channels with Ga/sub 0.62/In/sub 0.38/P barriers. For each composition, 1.1 /spl mu/m gate length devices with single and double barrier structures showed similar maximum drain currents (I/sub dmas/), and peak transconductances (g/sub m/), while the double barrier devices showed reduced output conductances (g/sub ds/) compared to the single barrier devices, resulting in a 30-50% larger voltage gain. RF measurements showed a higher maximum frequency of oscillation (f/sub max/) for the double barrier devices of both compositions. For mesa etch isolation of the double barrier devices, it was found to be necessary to remove the bottom GaInP barrier layer to achieve satisfactory device isolation. We speculate that a parasitic 2-dimensional electron gas may be formed at the interface between the bottom GaInP barrier and the GaAs buffer layer.