Photoluminescence, Reflectance and Photoreflectance Spectra in CdS Epilayers on Si(111) Substrates

Photoluminescence (PL), reflectance and photoreflectance (PR) spectra were measured on hexagonal CdS films grown directly on hydrogen-terminated Si(111) substrates with 3° off-orientation by hot-wall epitaxy technique. By comparing the PL spectrum to the reflectance and PR spectra in the excitonic energy range, we have unambiguously identified free A- and B-exciton transitions in the CdS films on Si(111) substrates. The peak energies of the A- and B-exciton transitions slightly shift to lower energy by about 3 meV than that of bulk crystal. This peak shifts were caused by a tensile strain parallel to the epilayer surface due to a difference of the thermal expansion coefficients between the grown CdS film and Si substrate. Donor–acceptor pair emission and defect-related “Y” bands as well as free and bound exciton peaks in PL spectra were also studied by means of their temperature (10–250 K) and excitation intensity dependences.