PHOTOLUMINESCENCE INVESTIGATION ON GROWTH MODE CHANGEOVER IN GE-RICH SI1-XGEX/SI STRAINED QUANTUM-WELLS

Growth mode transition during the high temperature growth of Ge-rich Si1-xGex/Si strained quantum wells (QWs) is investigated by photoluminescence (PL) spectroscopy. It is found that growth mode changeover takes place when the Ge composition of the QWs (L(x) = 32 Angstrom) exceeds 0.4, as observed by the upshift of emission energy from the calculation. It is also found that surface undulations, or islands, affect the growth of the succeeding QW when the barrier width is not thick enough (e.g. L(b) = 300 Angstrom). This is observed in the form of characteristic broad luminescence spectra with additional (NP, TO) pairs, which are in contrast to the phonon-resolved PL spectra of the multiple QWs with thicker barrier width (e.g, L(b) = 3000 Angstrom). From the results of PL measurement and transmission electron microscopy observations, we can conclude that barriers thicker than 1000 Angstrom are needed to successfully restore the surface flatness and obtain luminescence features specific to the single QWs.