Growth studies and characterisation of In2S3 thin films deposited by atomic layer deposition (ALD)

Abstract

An increased attention is devoted to interfacial In2S3 thin films because of their potential application as a new generation of buffer layer in copper indium gallium diselenide (CIGS)-based solar cells. In this paper, thin films of In2S3 were deposited on soda lime glass and SnO2-coated glass using indium acetylacetonate (In(acac)3) and H2S precursors by atomic layer deposition (ALD), a sequential chemical vapour deposition technique allowing the formation of dense and homogeneous films. The effect of temperature on the film kinetics has been studied. In a temperature window between 130 and 260°C, a maximum growth rate of about 0.7Å per cycle is obtained at 180°C. The structure and morphology of films were characterised by XRD, SEM and TEM. The ALD-In2S3 thin films are crystallised in a tetragonal form with band gap values of about 2.7eV. Electrical properties have been addressed by using impedance measurements on semiconductor electrolyte junctions. The films are n-type semiconductors with a doping level around 1016–1017cm−3 and possess a good blocking behaviour under reverse bias. The flat band potential is about −1.1V versus MSE. These figures are close to those measured under similar conditions with CdS buffer layers and could explain the good cell performances obtained with ALD-In2S3.