Monte Carlo simulation of electron transport in delta-doped lattice-matched and strained-balanced InGaAs/InAlAs quantum wells

Abstract

Strained-balanced /InAlAs quantum well structures have been shown to generate high carrier density, high-mobility layers suitable for power field effect transistor (FET) applications. Doped channel devices allow higher carrier densities than modulation-doped structures but with reduced carrier velocities due to increased ionized impurity scattering. The amount of ionized impurity scattering may be reduced by the introduction of compositional grading in quantum wells which results in an increasing depth of the quantum well on the opposite side to the delta-doped plane. The grading is achieved by the use of a number of steps, where each step has a fixed value of x. An ensemble Monte Carlo simulation has been used to calculate the velocity-field characteristics of the conduction electrons confined within the quantum well in such a structure. Here the envelope wavefunctions for the confined electrons are calculated using a self-consistent Poisson-Schrödinger solver. Our velocity-field characteristics show good agreement with experiment for the three-step structure but the agreement is noticeably worse for lattice-matched and five-step structures. We have shown that a correlation between the low-field mobility and saturation velocity observed experimentally for GaAs/AlGaAs and quantum wells and theoretically for GaAs/AlGaAs quantum wells is also valid for the predicted results in these structures. A similar explanation to that provided for the GaAs/AlGaAs quantum wells is shown to hold here.