TIGHT-BINDING CALCULATION OF ELECTRONIC STATES IN A TRIANGULAR SYMMETRICAL QUANTUM-WELL

We study a V-shaped symmetrically graded quantum well, which has been investigated optically. The well width is 125 Angstrom and the Al conc entration x varies linearly from x = 0.36 at the barriers to x = 0 (pu re GaAs) in the middle of the well. In the present paper, numerical ca lculations of the well electronic states are made within the framework of the surface Green function matching method and the sp(3)s empiric al tight-binding model within virtual crystal approximation. An algori thm developed recently by the authors is applied to treat graded compo sition heterostructures. The e1-hh1, e2-hh2, and e1-lh1 calculated tra nsition energies are in fair agreement with experiment. The dependence of the transition energies on the well width and on the Al concentrat ion is studied. A comparison with the rectangular quantum well is made . The transition energies decrease when the well width increases and a re always higher than the same energies of the rectangular quantum wel l. All the transitions ace better resolved energetically for the trian gular quantum well. The energies of the transitions under study increa se when the Al concentration x increases, but this dependence is much stronger for the triangular quantum well. Spatial distributions of spe ctral strengths of the well states are also obtained.