Alloys; Energy gap; Gallium arsenide; Germanium; Magnetron sputtering; Optical properties; Semiconducting gallium; Silicon alloys; Substrates; Tin; X ray diffraction; X ray diffraction analysis; Band gap transition; Direct band gap; GaAs(001); High-resolution x-ray diffraction; Magnetron sputtering systems; Sn concentration; Structural and optical properties; Tin alloys