Characterization of Ag doped p-type ZnO films

Ag-doped ZnO thinf films have been fabricated by pulsed laser deposition. Thermal analysis and X-ray photoelectron spectroscopy (XPS) were systematically investigated to verify the doping mechanism of Ag doped ZnO thin film depending on deposition temperature. The fabricated p-type Ag doped ZnO films shows the hole concentration in the range from 4.9×10¹⁶ to 6.0×10¹⁷cm^-3. ZnO exhibits n-type conductivity due to its native defects, such as zinc interstitials and oxygen vacancies. This strong n-type conductivity of ZnO restricts the application and it is difficult to fabricate p-type conductive ZnO¹. Therefore, research on ZnO has been mainly focused on the simple synthesis of p-type ZnO and intrinsic ZnO having insulating properties using various techniques and studying its doping properties^2-4. Recently, Li et al.⁵ reported that a ZnO p - n diode could be fabricated using a structure of ZnO:Ag/ZnO homo-junction on n-Si substrate. In previous letter⁶, we also reported that Ag-doped p-type ZnO thin films have been fabricated and characterized. In this study, thermal analysis and X-ray photoelectron spectroscopy (XPS) were systematically performed to investigate doping mechanism of Ag doped ZnO thin film depending on deposition temperature,. Ag doped ZnO thin films were grown on (0001) sapphire substrates by pulsed laser deposition (PLD). The electrical properties of Ag-doped ZnO films have been investigated by Hall measurement. Thermal behavior of the samples was measured in the temperature range from 30°C to 400°C. XPS analysis of Ag doped ZnO thin films were performed to investigate the effects of deposition temperature on the film composition and the chemical bonding. Table 1 shows the Hall measurement results of the Ag doped ZnO thin film at various deposition temperatures. In our previous report⁸, we reported that the electrical properties are divided by different three temperature regions from 100°C to 175°C (region I), 175°C to 275°C (region II), and 275°C to 400°C (region III). In each region, Ag doped ZnO thin films exhibit various electrical properties, such as semi-insulating (region I), .p-type (region II), and n-type (region III) properties depending on deposition temperatures. In the case of Ag doped ZnO films deposited at the region I, it shows semi-insulator behavior with a low carrier concentration and high resistivity. While Ag-doped ZnO films deposited at the region II exhibit .p-type conductivity. The hole concentration, carrier mobility, and resistivity of p-type Ag-doped ZnO films are measured to be in the range from 4.9×10¹⁶ to 6.0×10¹⁷ cm ^-3, 0.29 to 2.32 cm²/Vs, and 34 to 54 Ω cm, respectively. The Ag doped ZnO films deposited at the region III show a transition from p-type to n-type conductivity with the electron concentration of up to 2.27×10²⁰ cm^-3. This means that a role of Ag atoms in ZnO is changed by depending on deposition temperature. Consequently, it is possible to control of conductivity of ZnO films from intrinsic ZnO to p-type ZnO using Ag dopant and suitable deposition conditions.