Effect of in situ CdCl2 treatment on spray deposited CdTe∕CdS heterostructure

$\mathrm{CdTe}$ thin films have been deposited without and with in situ ${\mathrm{CdCl}}_2$ treatment using spray pyrolysis technique. Scanning electron microscopy studies show enhanced grain growth in the presence of ${\mathrm{CdCl}}_2$ . Glancing incidence angle x-ray diffraction is used to observe the microstructural changes of $\mathrm{CdTe}∕\mathrm{CdS}$ heterostructure at different depths by changing the incident angle. Spraying of ${\mathrm{CdCl}}_2$ on $\mathrm{CdS}$ prior to $\mathrm{CdTe}$ deposition promotes $\mathrm{S}$ diffusion throughout $\mathrm{CdTe}$ film and also Te diffusion into $\mathrm{CdS}$ . There is an associated change in the microstress of the $\mathrm{CdTe}$ film at different layers. The films without ${\mathrm{CdCl}}_2$ treatment show compressive microstress varying from $-98\mathrm{to}-158\mathrm{MPa}$ with increasing incident angle. ${\mathrm{CdCl}}_2$ spray during $\mathrm{CdTe}$ deposition leads to compressive microstress varying from $-98\mathrm{MPa}$ at the interface to $-19\mathrm{MPa}$ near the surface and ${\mathrm{CdCl}}_2$ spray prior to $\mathrm{CdTe}$ deposition leads to a mildly tensile stress $\left(+20\mathrm{to}+40\mathrm{MPa}\right)$ . Photoluminescence spectra for $\mathrm{CdTe}$ films with the in situ treatment show a reduction in the band gap due to $\mathrm{S}$ diffusion as well as the reduction in the defect band intensity. An in situ ${\mathrm{CdCl}}_2$ treatment results in less surface oxidation compared to ex situ process, as seen from x-ray photoelectron spectroscopy study. A shift of $\sim 200\mathrm{meV}$ in the Fermi energy towards the valence band is also observed in valence band spectra after the in situ ${\mathrm{CdCl}}_2$ treatment.