PHONON-RESOLVED AND BROAD PHOTOLUMINESCENCE IN STRAINED SI1-XGEX ALLOY MBE LAYERS

In the photoluminescence (PL) spectra of Si1-xGex multi-quantum wells (MQW) grown by conventional solid source molecular beam epitaxy (MBE), phonon-resolved, near-bandgap transitions due to shallow dopant bound exciton or free exciton recombination were observed when the well thi ckness was less than 40-1000 angstrom, depending on x. Increasing the Si1-xGex well thickness caused the emergence of a broad, unresolved PL peak approximately 120 meV lower in energy than the expected bandgap energy. Interstitial-type platelets, less than 15 angstrom in diameter , were measured by plan view transmission microscopy to occur in densi ties that correlated well with the intensity of the broad PL peak. A p latelet density of approximately 10(8) cm-2 per well was sufficient to completely quench the phonon-resolved PL. Etching experiments reveale d that within a given MQW, the platelet density is lowest in the first grown well and progressively increases in subsequent wells with incre asing strain energy density, indicating that platelet formation is str ictly a morphological phenomenon and suggesting that a strain relaxati on mechanism is in effect before the onset of relaxation by misfit dis location injection.