Doping Effects on CdO Thin Films

This paper reports the properties of undoped CdO films and CdO films doped with the group VII element F and the group IV element Sn. The CdO films are made by low-pressure chemical-vapor deposition. We observe that undoped CdO films can achieve a carrier concentration of 10²¹ cm^-3, apparently by controlling the intrinsic defect. However, the electron mobility of these films is only around 2 cm² V^-1 s^-1. With fluorine doping, an electron mobility of ∼260 cm² V^-1 s^-1 has been achieved. However, low carrier concentration results because of the low solubility of F in CdO film. CdO films doped with both Sn and F demonstrate carrier concentrations of 10²¹ cm^-3 and reasonable electron mobilities of around 20 cm² V^-1 s^-1. Due to the small effective electron mass of CdO, a large Burstein-Moss shift is observed for films with high carrier concentration. The shift enables the fundamental absorption edges of undoped CdO films to reach 3.0 eV and 3.3 eV for films doped with both Sn and F.