Design and growth investigations of strained InxGa1-xAs/InAlAs/InP heterostructures for high electron mobility transistor application

Strained In_xGa_1-xAs/InAlAs modulation-doped heterostructures on InP have been studied theoretically and experimentally. Simulations based on self-consistently solving the Schrodinger-Poisson equations have been performed to investigate the influeuce of the design parameters, namely the layer thicknesses and the doping level in the barrier layer, on the carrier concentration n, in the channel. Modulation-doped heterostructures with a 100 Å strained indium-rich channel have been grown by molecular beam epitaxy for different indium compositions and growth temperatures. The highest performances in terms of n,×μ parameter, have been obtained for an indium concentration of 75% in the channel, at a growth temperature of 500°C. For higher indium concentration, the mobility drops sharply, which correlates with formation of misfit dislocations in the channel, observed on transmission electron microscopy micrographs of these structures. For an indium concentration of 75%, the mobility has been improved, first, by using a low V/III beam equivalent pressure ratio, that produces a close to stoichiometry material, second by using interface growth interruption under cation stabilization to reduce the interface roughness. HEMT devices have been processed on these heterostructures. The static I-V characteristics of 2×150 μm ² transistors revealed a 66% increase of the transconductance when the channel indium concentration is increased from 53% to 75%