High pressure study of the zinc phosphide semiconductor compound in two different phases

Elucidating the Phase Transformation and Metallization Behavior of Zinc Phosphide under High Pressure

Among the family of II₃V₂-type compounds, zinc phosphide (Zn₃P₂) occupies a unique position. As one of the most promising semiconductors well-suited for photovoltaic applications, Zn₃P₂ has attracted considerable attention. The stability of its structure and properties are of great interest and importance for science and technology. Here, we systematically investigate the pressurized behavior of Zn₃P₂ using in situ synchrotron radiation angle-dispersive X-ray diffraction (ADXRD) and in situ electrical resistance measurement under high pressure. The ADXRD experiment shows that Zn₃P₂ undergoes an irreversible structural phase transition under high pressure, beginning at 11.0 GPa and being completed at ∼17.7 GPa. Consistently, the high-pressure electrical resistance measurement reveals a pressure-induced semiconductor-metal transition for Zn₃P₂ near 11.0 GPa. The kinetics of the phase transition is also studied using in situ electrical resistance measurement and can be well described by the classical Avrami model. What's more, the new high-pressure structure of Zn₃P₂ is refined to be orthorhombic with space group Pmmn; the lattice parameters and bulk modulus of this high-pressure phase are determined as a = 3.546 Å, b = 5.004 Å, c = 3.167 Å, and B₀ = 126.3 GPa. Interestingly, we also predict a possible structural phase transformation of orthorhombic phase (Pmmn) to cubic phase (P4₂32) during the decompression process; this cubic Zn₃P₂ is metastable at ambient conditions. These experimental results reveal the unexpected high-pressure structural behaviors and electrical properties of Zn₃P₂, which could help to promote the further understanding and the future applications of Zn₃P₂ as well as other II₃V₂ compounds.

Phase transformation and disorder effect on optical and electrical properties of Zn3P2 thin films

The phase transformation of zinc phosphide (Zn(3)P(2)) thin films was detected through isochronal annealing process. The effects on isochronal annealing on the internal structural, optical and electrical properties of deposited Zn(3)P(2) thin films have been discussed. The films were prepared by thermal evaporation under constant preparation conditions of vacuum 1.3×10(-5)Torr, substrate temperature (300K), rate of deposition (∼1nm/s) and film thickness (480nm). The annealing process was carried out under vacuum for 2h at different temperatures ranging from 373 to 623K. X-ray diffraction patterns showed that the as-deposited films and those annealed at temperatures less than 623K exhibit amorphous structure, while the films annealed at 623K showed tetragonal polycrystalline structure. The optical transmission and reflection spectra were measured at the wavelength range of 190-2500nm. The absorption coefficient spectra and the degree of disorder as measured from the absorption edge were determined. The indirect and direct optical energy band gaps were evaluated for indirect allowed and direct allowed transitions for amorphous and polycrystalline films, respectively. The refractive index n(o) increases with raising the annealing temperature which refers to more condensation in the material. The electrical resistivity for Zn(3)P(2) films decreases exponentially with raising the annealing temperature up to 623K as influenced by structure transformation and decreasing the degree of disorder in the films.