  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.
