MOCVD Growth and Properties of Zn3P2 and Cd3P2 Films for Thermal Photovoltaic Applications

We report the growth and characterization (structural and electronic) of thin films of Zn₃P₂ and Cd₃P₂ grown by MOCVD. Heterojunctions of this pair of dopable semiconductors are being studied for applications as thermophotovoltaic devices. We have grown films of these materials on glass substrates, and X-ray diffaction studies confirm the phase formation and polycrystalline nature of the films. Optical absorption studies revealed three distinct transitions in the Zn₃P₂ films, at 1.3, 1.55, and 1.85eV (in agreement with literature values found in single crystals). Analysis of optical spectra of the films showed direct transitions at 0.62, 0.65, and 0.71eV. We also report measurements of photoconductivity and photoluminescence in these films. Hall effect measurements show the Cd₃P₂ films to be n-type with mobilities as high as 429cm²/Vs. Carrier lifetimes were also measured directly by a photoconductive decay technique. The films show promise for TPV devices, although fabrication of such multilayer devices is in only a preliminary stage.