Solar Energy Materials 12 (1985) 51-56 51 North-Holland, Amsterdam DEPOSITION OF Zn3P 2 THIN FILMS BY COEVAPORATION A. LOUSA, E. BERTRAN, M. VARELA and J.L. MORENZA Universitat de Barcelona, Departament d'Electricitat i Electrbnica, Avinguda Diagonal, 645, 08028 Barcelona, Spain Received 28 November 1984 The deposition of Zn3P 2 thin films on glass substrates by coevaporation of the elements has been made feasible by a previous deposition of In germs on the substrates. The obtained films, 1.5 ~m thick, as observed in the scanning electron microscope, show a grain size near to 1 p.m. The X-ray diffraction spectra indicate a weak orientation of the tetragonal crystallites in the (220,004) direction. From the V-IR transmission spectra of the films, a direct energy band-gap of 1.51 eV has been deduced. The dark conductivity is in the 10-5 S cm-l range and has thermal activation energies around 0.4 eV, which decrease with increasing deposition temperature. Moreover the films show a fairly high photoconductivity. 1. Introduction Zinc-phosphide, Zn3P2, is a direct band-gap semiconductor (Eg = 1.5 eV) which is considered as one of the more suitable materials for solar energy photovoltaic conversion [1-3]. Up to now, zinc-phosphide has been obtained only with p-type conductivity. This limits its applications to n-p heterojunctions, MS and MIS structures. Solar cells with a Mg-Zn3P 2 Schottky barrier on polycrystalline bulk material have shown an efficiency of 6% [2], and in the case of an all thin film structure, an efficiency of 4.3% [4]. In the heterojunction solar cells ZnO/Zn3P 2 [5] and ITO/Zn3P 2 [6], the efficiencies have been 2%. Several techniques have been tried for the deposition of Zn3P 2 thin films: compound evaporation [7], CSVT [8], reaction of zinc and phosphine in a hydrogen atmosphere [9], and coevaporation using the quasi-rheotaxial growth [10]. In this work we report the deposition of Zn3P 2 thin films on amorphous solid substrates by coevaporation of Zn and P. The results of the morphological, struct- ural, optical and electrical characterization of the obtained films are also presented. 2. Experimental Zinc and phosphorus were evaporated in a vacuum chamber with a base-pressure of 10 -4 Pa. The elements were contained in two graphite crucibles introduced in Joule heated furnaces with independent temperature controllers. 0165-1633/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)