Isoelectronic bound-exciton photoluminescence in strained beryllium-dope epilayers an/Si superlattices at ambient and elevated hydrostatic pressure

Photoluminescence (PL) from a beryllium-doped (Formula presented)(Formula presented) epilayer and three different beryllium-doped (Formula presented)(Formula presented)/Si superlattices (SLșs) commensurately grown on Si(100) substrates is examined at 9 K at ambient pressure and, for the epilayer and one SL, as a function of hydrostatic pressure. In each structure, excitons bind to the isoelectronic Be pairs in the strained (Formula presented)(Formula presented) layers. The zero-phonon PL peaks of the epilayer and the in situ doped 50-Å (Formula presented)(Formula presented)/100-Å Si SL shift linearly with pressure toward lower energy at the rate of 0.68±0.03 and 0.97±0.03 meV/kbar, respectively, which are near the 0.77-meV/kbar value for Si:Be. The PL energies at ambient and elevated pressure are analyzed by accounting for strain, quantum confinement, and exciton binding. A modified Hopfield-Thomas-Lynch model is used to model exciton binding to the Be pairs. This model, in which potential wells bind electrons to a site (that then trap holes), predicts a distribution of electron binding energies when an inhomogeneous distribution of potential-well depths is used. This accounts for the large PL linewidth and the decrease of linewidth with increasing pressure, among other observations. In SLșs, the exciton binding energy is shown to depend on the width of the wells as well as the spatial distribution of Be dopants in the superlattice. Also, at and above 58 kbar a very unusual peak is observed in one of the SLșs, which is associated with a free-exciton peak in Si, that shifts very fast with pressure (-6.02±0.03 meV/kbar).