Growth studies and characterisation of In ₂ S ₃ thin films deposited by atomic layer deposition (ALD)

An increased attention is devoted to interfacial In ₂ S ₃ 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 In ₂ S ₃ were deposited on soda lime glass and SnO ₂ -coated glass using indium acetylacetonate (In(acac) ₃ ) and H ₂ S 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 0.7 Å per cycle is obtained at 180°C. The structure and morphology of films were characterised by XRD, SEM and TEM. The ALD-In ₂ S ₃ thin films are crystallised in a tetragonal form with band gap values of about 2.7 eV. Electrical properties have been addressed by using impedance measurements on semiconductor electrolyte junctions. The films are n-type semiconductors with a doping level around 10 ¹⁶ -10 ¹⁷ cm ^-3 and possess a good blocking behaviour under reverse bias. The flat band potential is about -1.1 V 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-In ₂ S ₃ .