Photoluminescence investigation on growth mode changeover in Ge-rich Si 1− xGe x/Si strained quantum wells

Abstract

Growth mode transition during the high temperature growth of Ge-rich Si 1− x Ge x /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 z = 32 A ̊ ) 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 A ̊ ). 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 A ̊ ). From the results of PL measurement and transmission electron microscopy observations, we can conclude that barriers thicker than 1000 Å are needed to successfully restore the surface flatness and obtain luminescence features specific to the single QWs.