Microstructure Adjustment And Optical, Electrical And Magnetic Properties Of ZnO Films

ZnO is a direct band gap compound semiconductor, with a wide band gap (3.37 eV at room temperature) and a large exciton binding energy (60 meV). It is a potential candidate for applications in short-wavelength optoelectronic devices and magneto-optical devices to improve the storage density and access speed. It has been widely studied on fabrication of high quality ZnO films and the optical, electrical and magnetic properties of ZnO films, which is the focus in international research.In this dissertation, ZnO films were deposited by helicon wave plasma assisted radio frequency magnetron sputtering (HWP-RF sputtering) and pulsed laser deposition (PLD). The following aspects have been studied:(1) On the sapphire substrates, which were nitridated under different temperature, ZnO films were deposited by HWP-RF sputtering. The results showed that:when nitridated under high temperature, the films were highly c-axis orientated and ab orientated with small stress. Nitridated under low temperature, the films were well c-axis orientation and ab orientation with bigger stress. Nitridated under middle temperature, the film was low c-axis orientation with no ab orientation.(2) By adjusting working pressure of Ar+O2 mixture gas, undoped p-type ZnO films were successfully deposited by HWP-RF sputtering on sapphire substrate. The X-ray diffraction results showed that p-type ZnO films were highly c-axis orientated and ab orientated. By applying plenty of oxygen and improving concentration of active oxygen particles in the plasma, the intrinsic acceptor defects were easily formed and p-type conversion realized.(3) Using N2 as doping source, on n-type Si substrates, the p-type Al-N co-doped ZnO films were deposited by HWP-RF sputtering. By adjusting N2 gas flow, controllable growth of p-type ZnO films on n-type Si substrate was realized. Photoluminescence spectrum at 77 K with a characteristic of N related neutral acceptor bound excitons (A0X) was given. The mechanism of p-type conductivity realized by donor-acceptor co-doping was proposed, which is useful to the control of conductivity in ZnO films. (4) The c-axis orientated Mn-N co-doped diluted magnetic ZnO film with single phase was successfully deposited by HWP-RF sputtering. The sample showed high resistivity and ferromagnetic at room temperature. Raman spectra showed that Mn was doped into the lattice in the form of substitute Zn2+. In the absorption spectra the charge transfer transition between donor and/or acceptor ionization levels of Mn ions and the band continuum were explained.(5) The c-axis orientated Mn doped diluted magnetic ZnO films with single phase were successfully deposited by PLD on sapphire substrates. With increasing Mn concentration, the crystal quality improved, the grain size became larger, and the saturation magnetic moment per Mn ion decreased. The optical band gap of the films showed a red shift tendency and the charge-transfer transitions absorption of the Mn ions increased. Under external magnetic field, the analysis of left and right circularly polarized light absorption demonstrated that the absorption edge was characteristic for s,p-d exchange effects. The electrical measurement showed that the films were n-type conductivity. The carrier transfer at low temperature satisfied the variable-range hopping conductivity mechanism. The long carrier residence time of carrier is in favor of forming ferromagnetic films. The decrease of the saturation magnetic moment per Mn ion is closely related to the decrease of Zn vacancy and the increase of neighbor Mn ions.