Fabrication and characterization of CdTe thin films: insights into classical and cryogenic fabrication techniques

Abstract

This study investigates the CdTe thin films prepared using two distinct methods: classical and cryogenic techniques of thermal evaporation within a substrate temperature range of 100-573 K. X-ray diffraction (XRD) analysis revealed cubic (111) crystal growth across all substrate temperatures, transitioning to an amorphous structure as the temperature approached 100 K. The CdTe thin film produced at 200 K stood out with superior structural properties, characterized by the lowest surface roughness (R a = 1.1 nm) and a highly uniform grain structure, attributed to the soliton growth mechanism. The grain sizes of the thin films decreased from 53.6 to 14.8 nm with a decreasing substrate temperature, correlating with an increase in resistivity (1.88-3.87 x 103 Omegacm) and band gap energy (1.48-1.65 eV). The CdTe thin films produced at the substrate temperatures of 200 and 473 K were relatively more stoichiometric. Photoluminescence (PL) measurements highlighted the enhanced luminescence intensity near the band-edge at 200 K, further confirming the optimal stoichiometry and structural quality of CdTe films produced in this regime. The findings highlight that the cryogenic technique could provide a significant advantage for applications such as quantum dots or nano-optoelectronics, where nanoparticle size and distribution must be precisely controlled.