Combined in-depth scanning Auger microscopy and Raman scattering characterisation of CuInS2 polycrystalline films

Serveis Cientı́fico-Tècnics, Universitat de Barcelona, C/Lluis Solé i Sabarı́s 1-3, E-08028 Barcelona, Spain
Vacuum (Impact Factor: 1.86). 07/2001; 63(1):315-321. DOI: 10.1016/S0042-207X(01)00207-X


In this work, the combination of in-depth scanning Auger microscopy with Raman microprobe spectroscopy is applied for the detailed microstructural characterisation of CuInS2 (CIS) thin films. CIS films are used for the fabrication of high efficiency solar cell devices. These films are obtained by sequential sputtering of Cu and In layers on a Mo-coated glass substrate, followed by a sulphurisation step at 500°C in a rapid thermal processing furnace. In order to study this process, samples obtained at intermediate steps are investigated. The obtained data show the formation of the CIS phase already at the first stages of the sulphurisation process, although with a highly disordered structure. Moreover, segregation of CuS towards the surface is observed before sulphurisation is completed. This fact is accompanied by a significant increase of the structural quality of the CIS film, which allows for the fabrication of high efficiency solar cell devices. The performed analysis corroborates the strong complementarity between the used techniques for the detailed microstructural analysis of complex multilayer systems.

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    • "Recently, Scanning Auger Microscopy (SAM) was used for the first time in biological samples during the study of the sexual structures of yeasts (Swart et al., 2010). SAM is a powerful tool used in the semi-quantitative elemental analysis on extremely small samples and is usually used for the near-surface analysis of conductor and semiconductors while the sample is visualised by Scanning Electron Microscopy (SEM) (Calvo-Barrio et al., 2001; Hochella et al., 1986). SAM has also been used to perform in-depth studies where the Argon (Ar + ) ion gun has been used for targeted etching on materials such as semi-conductors (Calvo-Barrio et al., 2001). "
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    ABSTRACT: Post-growth treatments, such as annealing, sulfurization, etching as well as ageing, were performed on CuInS2 films prepared by RF reactive sputtering. Their effects on the structural, optical and electrical properties of the films were studied by means of x-ray diffraction (XRD) and scanning electron microscopy (SEM), optical transmission, and Hall effect measurement, respectively. Heating under vacuum at 500 °C for a certain duration causes recrystallization of the as-sputtered films. The secondary Cu–In phases coexisting in the films sputtered with an insufficient H2S flow during sputtering can be eliminated by annealing in H2S atmosphere at 500 °C for suitable duration. Meanwhile, the film structural as well as optical properties are enhanced. The electrical properties of the as-grown films changed dramatically with ageing in air, and annealing in vacuum or air. KCN etching removed CuxS segregations on the film surfaces and returned the film electrical property to its initial state.
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    ABSTRACT: This work reports a microstructural investigation of thermal processes in polycrystalline CuInS2 films for solar cell by the combination of both ex situ and in situ techniques. Processed films were obtained under Cu excess conditions by sequential Cu and In sputtering onto Mo-coated glass substrates and sulphurised at different temperatures in the range of 400–450 °C. These conditions lead to layers with coexistence of both chalcopyrite (CH) and CuAu polymorphic CuInS2 phases, as well as CuIn5S8. The analysis of the in situ Raman spectra measured during the annealing of the samples at 500 °C has allowed to monitor the existence of a polymorphic transformation of metastable CuAu ordered domains into the equilibrium chalcopyrite structure. In principle, this transformation takes place in the range of 400–500° C and correlates with the presence of a surface Cu2S layer. This agrees with the in situ analysis of the sulphurisation process. However, in some cases, a strongly enhanced CuAu to chalcopyrite transformation has been observed, which is not related to the presence of the Cu–S binary phase. The origin of this anomalous behaviour is still unclear, and seems related to the microstructure of the metallic precursors before sulphurisation. Finally, ex situ X-ray diffraction (XRD) and in-depth Auger electron spectroscopy (AES) composition measurements have allowed to characterise the CuIn5S8 to CuInS2 transformation which takes place during annealing.
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