Above-barrier states in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ multiple quantum wells with a thin cap layer

The effective-mass approximation in a transfer-matrix formalism is used to investigate above-barrier states in strained ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ multiple quantum wells (MQW’s). A condition for finding above-barrier states, semiconfined by a finite cap layer, is formulated. In the derivation of the transfer matrices, boundary conditions that include the discontinuity of the lattice constant in the growth direction are used. In a series of ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ MQW’s (4–6 periods, $x\simeq 0.1,$ with the topmost barrier used as a cap) the energies of the light-hole and heavy-hole excitonic peaks, involving both above-barrier and confined states, are observed by photoluminescence excitation spectroscopy (PLE) and polarized PLE. The experimental values are in very good agreement with the calculated ones, for transitions involving above-barrier as well as confined states, supporting the validity of our calculations.