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_0.85In_0.15As channels with Ga_0.51In_0.49P barriers, and Ga_0.70In_0.30As channels with Ga_0.62In _0.38P barriers. For each composition, 1.1 μm gate length devices with single and double barrier structures showed similar maximum drain currents (I_dmas), and peak transconductances (g_m ), while the double barrier devices showed reduced output conductances (g_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_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