Anomalous spectral shift of photoluminescence from MBE-grown strained Si_1-xGe_x Si quantum wells mediated by atomic hydrogen

An anomalous peak shift was observed in photoluminescence (PL) of Si_1-xGe_x Si quantum wells (QW) with abrupt compositional interfaces formed by solid source molecular beam epitaxy (SSMBE) with atomic hydrogen (AH). It is found that MBE growth of QWs on Si(100) with AH leads to a considerable spectral blue-shift in conflict with the predicted red-shift associated with an abrupt interface. This was found to be caused by well width reduction due to selective etching of Si by AH during MBE. In contrast, strained Si_1-xGe_x Si QWs grown on Si(110) using AH revealed an apparent spectral red-shift in good agreement with the abrupt interface formation through the suppression of the Ge surface segregation with AH. The result seems to be explained as due to a reduced Si etch rate of Si on the Si(110) surface compared to Si(100).