Diffusion of phosphorus and arsenic using ampoule-tube method on undoped ZnO thin films and electrical and optical properties of P-type ZnO thin films

To investigate ZnO thin films, which are in the spotlight of next generation short wavelength LEDs and semiconductor lasers, the ZnO thin films were deposited using RF sputtering system in this study. The substrate temperature and work pressure were set at 300 °C and 5.2 mTorr, respectively, in the sputtering process of ZnO thin films and ZnO 5N was used as the purity target. The thickness of ZnO thin films was about 2.1 μm at the time of SEM analysis after the sputtering process. Phosphorus (P) and arsenic (As) were diffused in an ampoule tube of below 5×10−7 Torr into the undoped ZnO thin films sputtered by RF magnetron sputtering system. The doping sources of phosphorus and arsenic were Zn3P2 and ZnAs2. The diffusion of these elements was performed at the temperatures of 500, 600, and 700 °C for 3 h. Diffusion process of the conductive ZnO thin films, which have n-type and p-type properties, has been discovered. The ZnO thin films in this study showed not only very high carrier concentration of above 1017/cm3 but also low resistivity of below 2.0×10−2 Ω cm.