Material characterisation of InGaAs/InAlAs heterostructure field effect transistors with heavily doped n-type InAlAs donor layer

The impact of donor layer doping on InGaAs/InAlAs HFETs lattice matched to InP substrates is discussed. Several HFET layers with different donor concentrations and doped and undoped surface layers were grown by MBE. Using optical contact lithography, high performance devices (L_G=0.8 μm, f_max>120 GHz) were prepared for characterization using DC, RF, Hall, TLM, PL, and photocapacitance measurements. High channel concentrations (n_s>4×10¹² cm^-2) were achieved at very high doping levels in the donor layer (N_D =1×10¹⁹ cm^-3) and that surface doping does not improve device performance, but increases the output conductance and limits the range of usable drain bias. RF performance is mainly affected by the gate length of the device