ABOVE-BARRIER STATES IN INXGA1-XAS GAAS MULTIPLE-QUANTUM WELLS WITH ATHIN CAP LAYER/

The effective-mass approximation in a transfer-matrix formalism is use d to investigate above-barrier states in strained InxGa1-xAs/GaAs mult iple quantum wells (MQW's). A condition for finding above-barrier stat es, semiconfined by a finite cap layer, is formulated. In the derivati on of the transfer matrices, boundary conditions that include the disc ontinuity of the lattice constant in the growth direction are used. In a series of InxGa1-xAs/GaAs MQW's (4-6 periods, x similar or equal to 0.1, with the topmost barrier used as a cap) the energies of the ligh t-hole and heavy-hole excitonic peaks, involving both above-barrier an d confined states, are observed by photoluminescence excitation spectr oscopy (PLE) and polarized PLE. The experimental values;are in very go od agreement with the calculated ones, for transitions involving above -barrier as well as confined states, supporting the validity of our ca lculations.