Carrier Tuning in ZnSnN₂ by Forming Amorphous and Microcrystalline Phases

ZnSnN₂ (ZTN), an earth-abundant element semiconductor, is a potential candidate for photovoltaic applications. However, the excessively high n-type carrier concentration caused by intrinsic defects hinders its progress. In this work, a series of Zn_{1± x}SnN₂ thin films are fabricated by RF-magnetron sputtering deposition. The zinc-rich composition is found to promote the crystallization of ZTN. As a main source of n-type carriers in the zinc-rich thin films, the interstitial Zn dominates the change of carrier concentration with an increase in the Zn/Sn ratio. Near the stoichiometric ratio, amorphous ZTN (a-ZTN) thin films are fabricated, and the n-type carrier concentration is suppressed to 10¹⁶ cm^-3. With an increase in the Zn/Sn ratio from 0.9 to 1.3, the n-type carrier concentration can be tuned in the range 10¹⁶-10¹⁹ cm^-3, accompanied by the phase-transition from a-ZTN to microcrystalline ZTN (μc-ZTN). For the a-ZTN thin film, the carrier mobility reaches up to 7 cm² V^-1 s^-1, and the photoresponse covers almost the whole visible band. The above properties demonstrate that a-ZTN and μc-ZTN are potential candidates for photovoltaic applications.