Luminescence from Si/Si_1-xGe_x heterostructures and superlattices

A detailed study of near-gap photoluminescence (PL) from strained Si 1-xGex alloy layers (x=0.01-0.05) and Si/Si 0.95Ge0.05 multiquantum-wells (MQWs) has failed to show either free or dopant-bound excitons in as-prepared molecular beam epitaxial (MBE) layers. Low-temperature PL was, however, successfully induced in these same heterostructures by the selective introduction of relatively shallow (137 and 186 meV) radiation-damage bound-exciton centers, I1 and G, (respectively). The I1 center, in particular, produced alloy-broadened spectra which are shown clearly to emanate from the epitaxial layers, with separate and distinguishable components originating from both Si and Si1-xGex (x=0.01-0.05). This is among the first such reports of luminescence verifiably originating from within a Si/Si 1-xGex multiple heterostructure.