Tunneling and subband levels in GaAs quantum well with direct and indirect AlxGa1−xAs barriers

Abstract

We present a study of coherent tunneling lifetimes for quasibound electrons confined in a GaAs quantum well by Al0.3Ga0.7As (direct band gap) and AlAs (indirect band gap) barriers, using the tight‐binding representation for the electronic states in an eight‐element (sp3) basis, and solving the time‐dependent Schrödinger equation using a unitary approximation of the evolution operator. The dependence of the lifetime on barrier thickness is found to fit a WKB‐type expression very well. Although simple effective mass theory is not applicable, the barrier thickness coefficient in the WKB exponent is determined by the Γ‐point band extrema even for indirect AlAs barriers with X‐point conduction‐band minimum. The dependence of the subband energies and their in‐plane dispersion on the mole fraction x of Al in the AlxGa1−xAs barrier is also presented, for x in the range 0.2–1.