Study of the growth of CuAlS2 thin films on oriented silicon (111)

Within the chalcopyrite family the sulphur based compounds CuMS2 (M = In, Ga, Al) have attracted much interest in recent years because they show a direct wide band-gap covering from Egap = 1.53 eV (CuInS2) over Egap = 2.43 eV (CuGaS2) to Egap = 3.49 eV (CuAlS2). Therefore they are particularly suitable for optoelectronic as well as photovoltaic applications. The CuAlS2 semiconductor is one of these compounds and has good luminescent properties and a wide direct gap of 3.5 eV making it suitable for the use as material for light-emitting devices in the blue region of the spectrum. To dig up fully its potential a better understanding of the fundamental properties of the CuAlS2 film itself is essential, which could be achieved from high-quality single-crystalline materials. So, the aim of this work has been to study the growth of multilayer CuAlS2 thin films on Si(111) substrates at a substrate temperature of 723 K. One, two and three layers with 60, 120 and 180 nm thicknesses, respectively, were deposited on Si(111) substrate. The effect of the CuAlS2 layer numbers on the structure, morphology and optical properties of the samples was investigated. The X-ray diffraction studies revealed that all the samples are polycrystalline in nature, single CuAlS2 phase and exhibiting chalcopyrite structure with a preferred orientation along the (112) direction. However, the sample with three CuAlS2 layers exhibit the highly oriented (112) plane with grain sizes of 80 nm. So we show that this experimental process affects significantly the structural properties of the CuAlS2 films. Raman spectroscopic measurements indicated five prominent peaks at 193, 205, 325, 335 and 370 cm− 1. The possible origin of the 370 cm− 1 peak was investigated and was found to be some local vibration in the structure. The peaks at 193–205 and 335 cm− 1 were ascribed to A1 and B2 modes, respectively.