Thin film synthesis of SrZn2P2 with SrI2 post-annealing for enhanced crystallinity and optoelectronic quality

TL;DR

This study presents a method for synthesizing high-quality SrZn2P2 thin films with improved crystallinity and optoelectronic properties through halide-assisted post-annealing, advancing Zintl phosphide applications.

Contribution

It introduces a halide-assisted annealing process that enhances microstructure and optoelectronic quality of SrZn2P2 thin films, a novel approach for Zintl phosphide semiconductors.

Findings

SrZn2P2 films are phase-pure and crystalline after RF co-sputtering.

SrI2 annealing improves grain size and photoluminescence uniformity.

Annealing at 450°C with SrI2 significantly boosts photoluminescence intensity.

Abstract

Ternary Zintl phosphides are promising light-absorbing semiconductors for thin-film optoelectronic applications, but strategies for controlling their microstructure and optoelectronic quality remain underexplored. Here, we report the synthesis of phase-pure SrZn2P2 thin films using radio-frequency co-sputtering in a PH3 + Ar atmosphere and investigate the impact of post-growth processing on their structural and optical properties. Grazing-incidence X-ray scattering and Raman spectroscopy confirm the formation of crystalline SrZn2P2 films over a finite compositional window. Optical measurements reveal strong absorption near the direct-band-gap energy (~1.8 eV) and near-band-edge photoluminescence. Further, we have studied the effects of chemically compatible halide-assisted annealing. It is found that SrI2 treatments lead to pronounced grain growth and reduced diffraction peak broadening while preserving phase purity, in contrast to rapid thermal or forming-gas annealing. Notably, annealing with SrI2 at 450 {\deg}C significantly enhances both the intensity and spatial uniformity of the photoluminescence, thus connecting the observed microstructural consolidation with improved radiative recombination. Our study demonstrates that halide-assisted annealing provides an effective pathway for microstructural control in SrZn2P2 thin films and highlights a generalizable processing strategy for advancing Zintl phosphide semiconductors toward optoelectronic applications.