Band structure and charge control studies of n- and p-type pseudomorphic modulation-doped field-effect transistors

Abstract

We present results of a numerical formalism developed to address the band structure and the charge control problem in pseudomorphic n- and p-type modulation-doped field-effect transistors (MODFETs), which are created by adding excess indium in the active channel region. For n-type structures, the tight-bonding formalism is used to study the effect of strain on the crystal electronic properties. A finite-difference technique to solve the Schrödinger equation simultaneously with the Poisson equation is used to model the MODFET. The enhanced performance in n-type pseudomorphic devices has been shown to be primarily due to better charge confinement. Results are also presented as a function of channel strain. For p-type structures, the Kohn–Luttinger formulation is used together with deformation potential theory to describe the hole states. Significant reductions in the mass of the hole gas due to biaxial compressive strain are demonstrated, suggesting dramatic potential improvement in the operation characteristics of p-type pseudomorphic devices. As an application of the formalism, a comparison of pulse and uniform doping in the barrier region is carried out. The improvement in carrier transfer efficiency and the potential reduction of gate leakage current are discussed.