Zinc phosphide thin films grown by RF sputtering

Abstract

Zinc phosphide (Zn3P2) thin films have been prepared by RF sputtering in either Ar, H2, or PH3 atmospheres. The Zn3P2 films were deposited on glass substrates at RF power Ps of 50–300 W, substrate temperature Ts of 60–250°C, and total pressure up to 1 Torr. The Zn3P2 films grown in PH3 show a strongly preferred orientation; the c-axis is aligned perpendicular to the glass substrates, whereas the films grown in Ar and H2 are amorphous. The crystallinity of Zn3P2 films grown in PH3 depends strongly on both PH3 pressure Pp and RF power: below Ps=150 W the films are amorphous, while they are polycrystalline above it; the Zn3P2 films are polycrystalline below Pp=0.6 Torr, whereas they are amorphous above it. The X-ray fluorescence analysis and EPMA indicate Zn3P2.03 for the films deposited at Pp=0.2 Torr, Ps=200 W, and Ts=100°C. Optical measurements show that the film has a 1.5 eV direct bandgap.