Studies On Chalcogenide Semiconductor Thin Films Prepared By Ion Layer Gas Reaction Method (ILGAR)

In past decades, considerable attention has been given to nanocrystallinephotovoltaic cells (NPC) because of its simple process, low cost and large scaleproduction. In this paper, developments of NPC cells and its absorbers were reviewed,and a novel chemical deposition method-ILGAR was studied to fabricate metalchalcogenide thin films for NPC.CdS and CuInS2 thin films, as buffer and absorber layer respectively, werefabricated by ion layer gas reaction method (ILGAR), and the influence ofpreparation conditions on the film properties was investigated, such as absorptionways of the cations in precursor solution, the type of solvents, the concentration andratio of mixed precursors, sulfidation temperature, heat-treatment temperature, timeand atmosphere, Ga-doping. The characterizations for films were carried out byX-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectronspectrum (XPS), optical absorption spectrum and Hall system.The results show that CdS thin films fabricated by ILGAR method are uniform,compact and good in adhesion to substrate, and growth ratio of the film is 2.8 nm/cycle as [Cd2+]=0.05M. The evolution of structure undergoes from cubic tohexagonal with a preferred orientation along (002) plane after annealing of theas-deposited films at 400 ℃.ILGAR method for CuInS2 films was developed firstly by using ethanol assolvent and mixed cation precursor. Chalcopyrite CuInS2 film with near stoichiometryderived from [Cu+]/[In3+]=1.55, which is uniform, compact and good in adhesion tothe substrates, can be obtained after annealing in Ar atmosphere for 1h. Withincreasing the [Cu+]/[In3+], the absorption coefficients of CuInS2 films are more than104 cm-1, and the band gap changes from 1.40 to 1.30 eV, the resistivity, the carrierconcentration and the mobility is in the range from 50 to 10 ?-cm, 1015 to 1017 cm-3 and 2to 7 cm2/V·s, respectively.In the study of Ga-doping, single phase CuIn1-xGaxS2 thin films can be obtainedas [Ga3+]/[In3+] in mixed cationic solution is below 1, while [Ga3+]/[In3+] is above 1,two ternary compounds CuInS2 and CuGaS2 instead of CuIn1-xGaxS2 occur inannealed films.