Gate-controlled modulation of charge transport in long-channel, δ-doped, heterojunction Hall-bar structures

Abstract

The charge-transport properties of the two-dimensional electron gas (2DEG) generated by δ-doping lattice-matched InxGa1−xAs/InyAl1−yAs heterojunctions, x≤0.4, grown on GaAs substrates by means of compositionally step-graded, strain-relaxed, InyAl1−yAs buffer layers were investigated. Gate-controlled, long-channel, eight-arm Hall-bridge specimens using Shubnikov–de Haas (SdH) oscillatory magnetoresistance measurements, made at 1.6 K, low-field Hall-effect and resistivity measurements, and field-effect transistor measurements were made on the same specimens at 1.6 and 77 K. Fast Fourier transform analysis of the SdH data indicates that the displacement of the Fermi level produced by a quasistatic applied gate voltage can populate one, two, or three subbands of the 2DEG in its quantum well. The experimental data are in good agreement with theoretical Poisson/Schrödinger simulations of the equilibrium properties of such gate-controlled heterostructures. The effective electron density, mobility, and threshold voltage of the 2DEG are affected strongly by the density, distribution, time constants, and field-effect modulation of the deep-level electron traps present in the InyAl1−yAs charge-supply layer. Low-frequency transistor characteristics are consistent with a simple, long-channel, modulation-doped field-effect transistor model employing the parameters derived from the quasistatic measurements, gradual channel approximation rules, and current saturation affected by electron diffusion.