Spectroscopic study of Si-based quantum wells with neighbouring confinement structure

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Abstract
The optical properties of a neighbouring confinement structure (NCS), a promising candidate for a Si-based light emitter, were systematically investigated by using continuous-wave and time-resolved photoluminescence (PL) spectroscopy. An NCS consists of a single pair of a tensilely strained Si layer, a quantum well (QW) for electrons, and a compressively strained layer, a QW for holes, embedded between relaxed layers. Intense PL with an enhanced no-phonon (NP) line was clearly observed from NCS in spite of the indirect band structure in real and k-spaces. The quantum confinement effect was clearly observed by varying the well width, showing that the enhanced NP lines do come from the expected transitions of the NCS. Post-growth annealing was found to lead to selective quenching of the NP line compared to its transverse optical phonon replica (TO). Time-resolved PL study clarified that the radiative lifetime of the annealed sample increases with increasing temperature, while that of the as-grown sample shows no significant change at low temperatures ( K). These results were reasonably explained by considering that the exciton localization at the heterointerface is the controlling mechanism for the NP enhancement observed at low temperatures in the as-grown NCS. The idea was supported by the increase of the critical temperature for exciton delocalization by using a pure-Si/pure-Ge pair as the active layers, which is considered to construct a deep localization potential through the interface roughness.