Effect of the combination of Cu and CdTe plasmas on the structural and optical properties of CdTe:Cu thin films deposited by laser ablation

Abstract

In this work, thin films of semiconducting copper doped cadmium telluride (CdTe:Cu) were obtained by laser ablation. The effect of the combination of CdTe and Cu plasmas by the simultaneous ablation of Cu and CdTe targets, on the properties of CdTe:Cu films, when the copper plasma parameters (mean kinetic ion energy and density) are varied while CdTe plasma parameters were kept constant, is analyzed. The mean kinetic ion energy of Cu plasmas was increased from 73 to 100 eV. Cu plasma density increased linearly with mean kinetic ion energy. Mean kinetic ion energy and density of CdTe were kept constant at 75 eV and 2 × 1014 cm−3, respectively.The chemical composition was measured by energy dispersive X-ray spectroscopy. It was observed that Cu content incorporated into the CdTe lattice varied from 1.4 to 1.6 at%. Structural characterization revealed the growth of a CdTe hexagonal structure with no preferential orientation for a reference CdTe film. For samples grown combining Cu and CdTe plasmas, it was observed that increasing density of Cu plasma produces a crystalline orientation of the films in the (110) direction. Optical properties of the samples were obtained by UV–Vis spectroscopy, the data was used to estimate band gap using Tauc plots yielding values that decreased slightly form 1.47 eV for the reference CdTe film, to 1.41 eV for the film grown using the highest Cu plasma density. Scanning electron microscopy was used to study surface morphology, were rougher surfaces were observed as the Cu content in the films was increased.