Analysis of the Persistent Photoconductivity of Zinc Tin Nitride

Zinc Tin Nitride (ZnSnN2) is a semiconductor that is being explored for its potential use in photovoltaic applications. It is attractive due to its composition of non-toxic, Earth abundant elements. In this work, we study the photoconductivity behavior of a thin film of ZnSnN₂ as a function of time and temperature. Initial light exposure results in a very slow rise of conductivity to an eventual plateau, which is more pronounced at lower temperatures. When the light exposure is turned off, the photoconductivity decays very slowly, exhibiting persistent photoconductivity. The time decay characteristics of the conductivity can be modeled by a stretched exponential function. The persistent conductivity decay characteristics further have a pronounced temperature dependence, and we find that it is well-described by a thermal activation process with activation energy around 0.3  - 0.4 eV. We propose a model for the relaxation of photocarriers back to the conduction band that involves disorder-induced carrier traps, with a broad range of characteristic trap lifetimes. Our analysis leads to a proposed distribution of trap state energies within the bandgap of Zinc Tin Nitride.