Cadmium sulfide (CdS) is an interesting material for applications in optoelectronic and pho- tovoltaic devices. In particular, thin films of n-type CdS are widely used as a window layer in heterojunction solar cells. The optical bandgap energy is the most interesting parameter for these applications. For spray-deposited indium-doped cadmium sulfide (CdS:In) thin films prepared on glass substrates the transmittance measurements were used to estimate the optical bandgap energy. Tailing in the bandgap was observed and found to obey Urbach rule. The effects of film thickness and the substrate temperature on the bandgap energy and the width of the tail were investigated. A linear relation between bandgap energy and width of the tail was found.

https://cyberleninka.org/article/n/1221045.pdf

A study of the optical bandgap energy and Urbach tail of spray-deposited CdS:In thin films

Structural and optical investigations on CdS thin films grown by chemical bath technique

Growth, characterization and studying of sol–gel derived CdS nanoscrystalline thin films incorporated in polyethyleneglycol: Effects of post-heat treatment

Here we present experimental evidence of the strong modification of the CdS photoluminescence when it is embedded in a SiO2 colloidal photonic crystal. When the emitted light matches a forbidden photonic band in the matrix, inhibition of the semiconductor photoluminescence is achieved. In this work we prove the effective control of this effect by means of the photonic lattice parameter of the host. CdS was grown by chemical bath deposition and its quality has been checked employing Raman spectroscopy and x-ray diffraction. Scanning electron microscopy is used to study the morphology of the composite.

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CdS photoluminescence inhibition by a photonic structure

Photoluminescence (PL) measurements were used to study the effect of postdeposition treatments by annealing and CdCl2 activation on polycrystalline CdS layer grown by close-spaced sublimation (CSS) and chemical bath deposition (CBD). CdS films were either annealed in a temperature range of 200–600 °C or CdCl2 treated between 300–550 °C. The development of “red,” “intermediate orange,” “yellow,” and “green” luminescence bands is discussed in comparison with PL assignments found in literature. PL spectra from CdS layer grown by CSS are dominated by the yellow band with transitions at 2.08 and 1.96 eV involving (Cdi-A), (VS-A) complex states where A represents an acceptor. Green luminescence bands are observed at 2.429 and 2.393 eV at higher annealing temperature of 500–600 °C or CdCl2 treatment above 450 °C, and these peaks are associated with zero and a longitudinal optical phonon replica of “free-to-bound” transitions. As grown CBD-CdS films show a prominent red band with four main peaks located at 1.43, 1.54, 1.65, and 1.77 eV, believed to be phonon replicas coupled with local vibrational modes. This remains following postdeposition treatment. The red luminescence is associated with VS surface states and in the case of CdCl2 treatment with (VCd-ClS) centers. Postdeposition treatments of CBD and CdS promote the evolution of an intermediate orange band at 2.00 eV, most likely a donor-acceptor pair, and a yellow band at 2.12 eV correlated with (Cdi-VCd) centers. The green luminescence bands observed at 2.25 and 2.34 eV are associated with transitions from deep donor states (e.g., Cdi) to the valence band. These states form due to crystallinity enhancement and lattice conversion during annealing or CdCl2 activation. Observed changes in PL bands provide detailed information about changes in radiative recombination centers in CdS layer, which are suggested to occur during device processing of CdTe/CdS thin film solar cells.

/pdf/photoluminescence-study-of-polycrystalline-photovoltaic-cds-1n888kckb0.pdf

Photoluminescence study of polycrystalline photovoltaic CdS thin film layers grown by close-spaced sublimation and chemical bath deposition

Spectral photoconductivity, photoconductive quenching, photoluminescence, and thermally stimulated current measurements, have been carried out in order to study the evolution of defect energy levels in CdS thin films, grown in cubic phase by chemical bath deposition, as a function of thermal annealing temperatures in Ar+S2 atmosphere. The results are influenced by a cubic-to-hexagonal phase transition. From those measurements, a number of trap levels and deep levels in the forbidden band are determined. The results can be explained in terms of the evolution of native and phase transition generated defects in the sample structure.

M. Garcia-Rocha

Papers

Characterization of defect levels in chemically deposited CdS films in the cubic-to-hexagonal phase transition