ANOMALOUS PHOTOLUMINESCENCE OF PURE-GE SI TYPE-II COUPLED QUANTUM-WELLS (II-CQWS)/

Anomalies have been observed in photoluminescence (PL) of pure-Ge/Si t ype-II coupled quantum wells (II-CQWs). Although the II-CQWs (L-Ge = 1 .5 ML) showed clear energy red-shift with decreasing Si spacer thickne ss (Lsi) due to interwell coupling of the hale wavefunction, an anomal ous energy lowering was observed for smaller L-Si (less than or equal to 6 Angstrom). Moreover, PL intensity of the II-CQWs increased linear ly with increasing excitation power, as opposed to a sublinear increas e in type-II QWs due to exciton localization at the interfaces. These results seem to be the result of enhanced electron capture by the II-C QW potential profile. Furthermore, correlation of thickness fluctuatio n among the layers was observed by high-resolution transmission electr on microscopy, which may be connected to the PL anomalies.