Tunneling and Subband Levels in a GaAs Quantum Well with Direct and IndirectAl(x)Ga(1-x)As Barriers

摘要

We present a study of coherent tunneling lifetimes for quasibound electronsconfined in a GaAs quantum well by Al(0.3)Ga(0.7)As (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 Schrodinger 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 r-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 Al(x)Ga(1-x)As barrier is also presented, for x in the range 0.2-1.