Gallium phosphide protective infrared films on zinc sulphide deposited by RF-planar magnetron sputtering

摘要

GaP thin film has proved to be effectively protective coating for zinc sulphide long-wave infrared (8-11.5 μm) window or dome from sand abrasion and raindrop erosion. The GaP films are deposited on thermo-pressed 5-mm-thick planar ZnS substrates of 20 mm in diameter by RF-planar magnetron sputtering in high pure argon gas, with a single crystalline GaP disc of 50 mm in diameter as the target. Following parameters vary from experiment to experiment with others kept unchanged: input RF powers are increased from 30 W to 100 W as feeding gas flows and gas pressures in the vacuum chamber are decreased simultaneously, with the intensity of the 750-nm-wavelength ray of argon's OES observed through a CCD multichannel spectrometer in glow discharges remaining almost the same. Thus different sets of deposition parameters are gained. Within these sets of parameters, the deposition rates and the degree of crystallization of the films increase with the input RF power increasing, as the IR transmission performances are as good, and thus thick GaP films with little absorption are achieved. SEM analyses show that the GaP films are compact and glazed