Fabrication and characterization of RF-magnetron sputtered gallium arsenide, arsenic selenium telluride, and silicon thin films

RF-magnetron sputtered amorphous and microcrystalline GaAs, AsSeTe, and Si thin films were fabricated with various sputtering parameters which consist of substrate-holder temperature, sputtering pressure, sputtering power, and hydrogen partial pressure. The experimental goals of this dissertation are to fabricate GaAs, AsSeTe, and Si thin films with a low optical absorption coefficient and a high index of refraction for potential applications in the near and mid-infrared wavelength ranges. Most of the sputtered samples exhibit optically smooth surfaces as examined by optical microscopy and atomic force microscopy (AFM). Some GaAs and AsSeTe samples show delamination which can be eliminated by back-sputtering and bias sputtering. Shaling is found on GaAs samples sputtered with high hydrogen partial pressure (>7.5 mTorr). The surface roughness of GaAs samples varies with sputtering parameters. The results show that the higher the sputtering pressure and self-bias potential, the higher the RMS roughness.; The film stress measured by Michelson interferometry varies with different sputtering parameters. A significant discovery is that GaAs films sputtered below 5 mTorr yield compressive stress while GaAs films sputtered over 10 mTorr yield tensile stress. There exists a transition pressure between 5 mTorr and 10 mTorr. Time-dependent stress variations are found on samples sputtered at 10 mTorr/200°C/400 W in 25% H₂/75% Ar and 10 mTorr/150°C/400 W in 75% H₂/25% Ar. The optical absorption coefficient a varies with different sputtering parameters; a decreases with increasing substrate temperature (up to 200°C), sputtering pressure (up to 20 mTorr), sputtering power (up to 800 W), and hydrogen partial pressure (up to 7.5 mTorr). The optical results show that GaAs samples sputtered at 800 W/200°C/10 mTorr in a 25% H₂/75% Ar gas mixture yield α below 100 cm −1 beyond 1250 nm wavelengths. This result represents the lowest reported value of α for sputtered GaAs films as measured by spectrophotometry. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the sputtered GaAs films consist of amorphous and microcrystalline phases. A sharp transition with increasing sputtering temperature is found from purely amorphous GaAs to a mixture of microcrystalline GaAs in an amorphous matrix.