Temperature dependences of the intensity and the position from photocurrent and photoluminescence spectra in CdS layers

Using the hot wall epitaxy method, we grew CdS epilayers on GaAs substrates. From the photocurrent (PC) measurement, the peaks corresponding to excitons A and B were observed in the short-wavelength region. Also, a crystal field splitting of 0.026 eV was extracted through the PC spectroscopy method. The PC intensities decreased with decreasing temperature. In the log J ph vs. 1/T plot, the dominant level was observed in the high-temperature region, and its activation energy was 33.9 meV. From the photoluminescence (PL) experiment, the PL intensities of the free exciton were exponentially reduced with increasing temperature. From the relations of log I PL vs. 1/T, an activation energy of 29.7 meV was observed in the high-temperature region. By comparing the PC and the PL results, we found that these activation energies were the thermal dissociation energies of the free exciton at the ground state and corresponded to the binding energies of the free exciton. Thus, we suggest that this trapping center limits the PC signal with decreasing temperature. Furthermore, the band gap energy of CdS as a function of temperature was well described by E g (T) = 2.581 − (6.1 × 10−4)T 2/(248 + T).