PHOTOLUMINESCENCE PROPERTIES OF STRAINED MOLECULAR-BEAM EPITAXY SI1-XGEX/SI MULTIQUANTUM WELLS

Si1-xGex/Si multiquantum well (MQW) structures grown by molecular-beam epitaxy exhibit a broad, intense photoluminescence (PL) peak approximately 120 meV below the band gap energy and/or phonon-resolved, near-band gap PL, depending on the MQW strain and the growth conditions.The origins of these two PL types have been identified. For MQWs with thin alloy layers (< 4.0-100 angstrom), the SiGe PL at 2 K is dominated by boron bound-exciton annihilation, which yields phonon-resolved transitions. For thicker layers, the PL is dominated by a broad, intense peak due to exciton recombination at small (< approximately 15 angstrom) interstitial-type platelets that occur in densities up to approximately 10(9) cm-2/QW. Etching experiments revealed that within a given MQW the platelet density is lowest in the first grown well and progressively increases in subsequent wells with increasing strain energy density, indicating that platelet formation is strictly a morphological phenomenon.