Local excitons in silicon induced by SiGe quantum huts
Conversion of Si to a direct bandgap semiconductor for optoelectronic application is a great challenge for many decades. It is proposed that embedment of suitable sized quantum dots into silicon matrix may be exploited to convert silicon to a direct bandgap semiconductor. The other bottleneck to this outstanding issue is the identification of local excitons, a signature of direct bandgap property and their comportment within the dots that can be utilized in engineering optoelectronic devices, quantum communications, etc. We studied the core level spectra of Si/Ge quantum huts embedded Si employing high resolution photoemission spectroscopy. Inverted quantum huts (IQHs) of Ge (13.3nm x 6.6nm) were grown on a Si buffer layer deposited on Si(001) surface using molecular beam epitaxy method and the photoemission experiments were carried out at different locations of the IQH structures exposed via controlled sputtering and annealing processes. We discover distinct features in the Ge 3$d$ core level spectra at the lower binging energy side of the bulk 3$d$ peak in contrast to the scenario of core level satellites often observed due to photoemission final state effects. The energy of these features are found to be sensitive to the location of the IQH structure probed revealing different core hole screening by the excitons located at different parts of IQHs. These results reveal local character of the excitons in the IQHs necessary for type I photoluminescence and establish core level spectroscopy as a direct probe of local excitons. These finding are expected to help amalgamation of microelectronics and solid state photonics important for optoelectronic applications.