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 S i1-xGex/Si strained quantum wells (QWs) is investigated by photolumine scence (PL) spectroscopy. It is found that growth mode changeover take s place when the Ge composition of the QWs (L(x) = 32 Angstrom) exceed s 0.4, as observed by the upshift of emission energy from the calculat ion. It is also found that surface undulations, or islands, affect the growth of the succeeding QW when the barrier width is not thick enoug h (e.g. L(b) = 300 Angstrom). This is observed in the form of characte ristic broad luminescence spectra with additional (NP, TO) pairs, whic h are in contrast to the phonon-resolved PL spectra of the multiple QW s with thicker barrier width (e.g, L(b) = 3000 Angstrom). From the res ults of PL measurement and transmission electron microscopy observatio ns, we can conclude that barriers thicker than 1000 Angstrom are neede d to successfully restore the surface flatness and obtain luminescence features specific to the single QWs.