Revealing the structure and physical properties of Ba-based phosphide compounds: A theoretical study

Nitride and phosphide semiconductors AB2X2 (A = Ca, Sr; B = Zn, Cd; X = N, P) are the promising novel materials for optoelectronic applications. A comparative study is performed to reveal the stability, mechanical, electronic, and optical properties of Ba-based phosphide compounds. Our results indicate that it should have three stable structures (α, β, and γ phases) for BaZn2P2, while it only exists a γ phase for BaMg2P2 and BaCd2P2. This finding is reasonable consistent with the experimental results. Moreover, the dynamical, thermal, and mechanical stability of γ-BaZn2P2 and γ-Ba(Zn0.5Cd0.5)2P2 are verified. Three different phases of BaZn2P2 display completely different electronic features. The compound β-BaZn2P2 has a narrower band gap than those of α and γ analogues. An indirect to direct band gap transition is revealed for Ba(Zn/Cd)2P2 alloys. The γ-BaZn2P2 has an indirect band gap of 1.22 eV, while γ-Ba(Zn0.5Cd0.5)2P2 and γ-BaCd2P2 show direct band gaps of 1.27 and 1.40 eV. The optical properties of these compounds are discussed in detail. Our study finds that γ-Ba(Zn0.5Cd0.5)2P2 is a less-toxic, stable, and ductile material, and it also shows excellent optoelectronic properties including suitable direct band gap and strong optical absorption.