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Photoluminescence specroscopy of CdS and GaSe

Seyhan, Ayşe
With the use of photoluminescence (PL) spectroscopy one can able to get a great deal of information about electronic structure and optical processes in semiconductors by the aid of optical characterization. Among various compound semiconductors, Cadmium Sulfide (CdS) and Gallium Selenide (GaSe) are interesting materials for their PL emissions. Particularly, due to its strong anisotropy, investigation of GaSe necessitates new experimental approaches to the PL technique. We have designed, fabricated and used new experimental set-up for this purpose. In this thesis, we have investigated the PL spectra of both CdS and GaSe as a function of temperature. We observed interesting features in these samples. These features were analyzed experimentally and described by taking the band structure of the crystals into account. From the excitonic emissions, we determined the bandgap energy of both materials. We studied various peaks that appear in the PL spectra and their origin in the material. We have found that donor acceptor transitions are effective in CdS at low temperatures. A transition giving rise to a red emission was observed and attributed to a donor level which is likely to result form an S vacancy in CdS crystal. The PL peaks with energy close to the bandgap were observed in GaSe. These peak were attributed to the bound excitons connected either to the direct or indirect band edge of GaSe. The striking experimental finding in this work was the PL spectra of GaSe measured in different angular position with respect to the crystal axis. We observed that PL spectra exhibit substantial differences when the angular position of the laser beam and the detector is changed. The optical anisotropy which is responsible for these differences was measured experimentally and discussed by considering the selection rules of the band states of GaSe.