Effect of Iodine Incorporation on Characteristic Properties of Cadmium Telluride Deposited in Aqueous Solution

Abstract

The electrodeposition of polycrystalline I-doped CdTe was successfully performed from aqueous solutions containing cadmium nitrate (Cd(NO3)2) and tellurium oxide (TeO2). The effects of different I-doping concentrations in an electrolytic bath on the CdTe layers deposited were evaluated structurally, optically, morphologically and electronically using x-ray diffraction (XRD), ultraviolet–visible spectrophotometry, scanning electron microscopy, photoelectrochemical cell measurement and direct-current (DC) conductivity tests. The XRD showed reduction in the (111) cubic CdTe peak intensity and the calculated crystallite size of the CdTe:I layers above 5 ppm I-doping. At I-doping of 1000 ppm of the CdTe bath and above, we observed the deposition of only crystalline Te due to the formation of Cd-I complexes debarring the deposition of Cd and co-deposition of CdTe in aqueous solution. Morphologically, we found reductions in grain size above 5 ppm I-doping with high pinhole density and the formation of cracks within the CdTe:I layers. For the as-deposited CdTe:I layers, conduction type remained n-type across all the explored I-doping concentration of 200 ppm. For the CdCl2 and Ga2(SO4)2 + CdCl2 treated CdTe:I layers, a transition from n- to p-type conductivity was observed for the CdTe:I baths doped with 20 ppm and above due to the reduced cadmium deposition on the substrate. The highest conductivity was observed at 5 ppm I-doping of the CdTe bath. Observations made on the CdTe:I in aqueous solution differs from the non-aqueous solvent documented in the literature. These results are reported systematically in this communication.