Study On The Preparation And Properties Of ZncdO Thin Films

ZnO is a new II-VI compound semiconductor with a wide direct band gap. ZnO has a hexagonal wurtzite structure with the lattice parameters a=0.3249nm and c=0.5206nm. Due to its direct wide band gap(Eg=3.3eV at room temperature) and large exciton binding energy (60meV), ZnO is believed to be an ideal candidate material for the fabrication of optoelectronic devices operating in the ultraviolet region. In order to design the devices, an important step is to modulate the band gap of ZnO. ZnO incorporated with Cd element, to fabricate the ternary ZnCdO alloy, will result in the band gap red-shifted from the ultraviolet to a blue or even green spectral range.Two methods, pulsed laser deposition and RF reactive magnetron sputtering, were used to grow ZnCdO films, respectively. X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), field-emission scanning electron microscopy (SEM), atomic forced microscopy, transmission spectrum and photoluminescence (PL) are used to study the microstructure, content and the optical properties of the ZnCdO films. On the other hand, the electrical properties of ZnO and ZnCdO films were studied in micro-scale with conductive AFM. The results are summaried as follow:1ZnCdO films were grown on Si (001) substrate with pulsed laser deposition method at different deposition temperatures. All the films are highly c-axis textured. With increasing the temperatures, the diffraction peak of (002) shifts to the high angle and a film with high crystallinity could be prepared at600°C. The low-temperature PL spectra show that all the samples have the emissions both from ZnO and ZnCdO phases, suggesting the phase seperation takes place in the films. The low-temperature PL spectra indicate that ZnCdO phase dominates the PL emission in the film deposited at400°C.2ZnCdO films were grown on Si (001) substrate with pulsed laser deposition method at different oxygen pressures. The phase separation was observed in all the films and became more obvious with increasing the oxide pressure. The surface morphology was found to be dependent on the oxygen pressure. An obvious red-shift of the ZnCdO PL peak was observed at room temperature (RT). In the low-temperature PL spectra of films, the separation peaks of Zn-rich and Cd-rich phase was observed clearly and Zn-rich phase peak intensity rapidly decreases with the temperature increasing.3ZnO and ZnCdO films were grown by PLD on sapphire substrates with a Pt layer depositied with the magnetron sputtering method. The result shows that Pt layers affected the properties of the ZnCdO. ZnO and ZnCdO films were epitaxially grown on the Pt sublayer at0.02Pa. Low temperature PL spectra shows the films with the structure of ZnO/Pt/Sapphire have a new PL peak at400nm. On the basis of the first-principles calculations, the new PL emission is suggested to relate to Pt doping due to diffusion in the film growth. p-type conductance is predicted for the films of Pt-doped ZnO.