Optical and electronic properties of (Al Ga1−)2O3/Al2O3 (x>0.4) films grown by magnetron sputtering

Abstract Systematic investigations of the optical and electronic properties are reported for ultrathin (AlxGa1−x)2O3/Al2O3 films with higher Al contents x (>0.4) prepared by magnetron sputtering method. The X-ray diffraction results revealed the films were preferentially oriented in the direction of β-Ga2O3 ( 2 01) family and their crystalline qualities improved if prepared at higher sputtering power. From the X-ray photoelectron spectroscopy (XPS) data, the Al content x in the four (AlxGa1−x)2O3 samples are found to be 0.72, 0.67, 0.62 and 0.42, respectively. The composition dependent energy bandgaps E g (6.47 eV, 6.34 eV, 6.02 eV, 5.61 eV) observed by optical transmission and XPS measurements are examined theoretically. From the atomic ratios of (Al+Ga)/O and the observed photoluminescence features we suggest the possibility of large number of defects and/or vacancies. With higher Al contents, the Fermi level shifts towards the valence band and the work function increases. While lowering the sputtering power is helpful in preparing thin (AlxGa1−x)2O3 films with higher x – it is certainly not favorable for improving their crystalline quality and conductivity.