Intrinsic Defects and Dopability of Zinc Phosphide

TL;DR

This study investigates the intrinsic defects in zinc phosphide using advanced computational methods to understand its doping limitations, revealing that phosphorus interstitials hinder n-type doping by acting as electron sinks.

Contribution

It introduces a novel 'perturbation extrapolation' method to efficiently study large defect systems with hybrid functional calculations, providing insights into doping challenges.

Findings

Phosphorus interstitials have low formation energy and act as electron sinks.

Intrinsic defects limit n-type doping by lowering the Fermi level.

Results align with experimental observations of doping behavior.

Abstract

Zinc Phosphide ($Zn_3P_2$) could be the basis for cheap and highly efficient solar cells. Its use in this regard is limited by the difficulty in n-type doping the material. In an effort to understand the mechanism behind this, the energetics and electronic structure of intrinsic point defects in zinc phosphide are studied using generalized Kohn-Sham theory and utilizing the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional for exchange and correlation. Novel 'perturbation extrapolation' is utilized to extend the use of the computationally expensive HSE functional to this large-scale defect system. According to calculations, the formation energy of charged phosphorus interstitial defects are very low in n-type $Zn_3P_2$ and act as 'electron sinks', nullifying the desired doping and lowering the fermi-level back towards the p-type regime. This is consistent with experimental observations of both the tendency of conductivity to rise with phosphorus partial pressure, and with current partial successes in n-type doping in very zinc-rich growth conditions.