Zn/P ratio and microstructure defines carrier density and electrical transport mechanism in earth-abundant Zn3-xP2+y thin films

Scalable and sustainable photovoltaic technologies require low-cost and earth-abundant semiconducting materials. Zinc phosphide is purported to be an absorber material with optimal photovoltaic properties. Herein we report the electrical properties of Zn3P2 thin films with different crystallinity grown on InP substrates. The room temperature electrical resistivity of the as-grown single crystal thin films is found to be in the range of 42-1050 omega cm. We correlate the crystalline quality and composition to the electrical properties. Capacitance-voltage measurements and secondary ion mass spectroscopy demonstrate the direct correlation between the carrier concentration and the Zn/P ratio. The highest hole mobility value (125 cm2/Vs) was obtained from high-quality single crystalline Zn3P2 thin films. The electrical characteristics of the heterojunction between the thin film and the substrate were also illustrated. This work sheds light on the electrical properties and conduction mechanism, thus providing a better understanding of the limitations and potentials of the electrical devices related to the material.