Study On Band-gap Engineering Of ZnO Films Made By Reactive Radio-Frequency Magnetron Sputtering

ZnO is a II-VI wide-band-gap (～3.3eV at room temperature) semiconductor used in optical and electronic device applications such as light emitters, sensors, solar cells, transparent conductors for display and UV detectors. In terms of optoelectronics, its direct band gap and a large exciton banding energy (60meV) should in principle lead to low thresholds for optical gain even at room temperature. Now, a crucial step in designing ZnO-based optoelectronic devices is the realization of band-gap engineering to create barrier layers and quantum wells in device heterostructures. This work is focus on the optical and electrical properties of the ZnO-based materials, as follow:I Using reactive radio-frequency(RF) magnetron sputtering, ZnO films with strong c-axis orientation have been deposited on Si (100) substrates at temperatures ranging from room temperature (RT) to 750℃. We have studied the influence of growth temperature on the structural characteristics of the as-grown films in morphology, grain size, microstructure, and residual stress by using atomic force microscopy(AFM), transmission electron microscopy(TEM), x-ray diffraction(XRD), and Raman spectroscopy. With the measurement of the transmission spectra and PL properties, the relationship between the crystallinity and optical properties of ZnO films have been discussed. It is found that the grain sizes have an increase behavior with temperature up to 500℃, and then decrease at 750℃. ZnO grains have an epitaxial relationship with Si (100) substrate for the films deposited at the temperatures ranging from RT to 750℃. The films deposited below 500℃ are in the states of compressive strain while the film deposited at 750℃ is in tensile. The difference in growth temperature results in the variation of refractive index, extinction coefficient, optical energy gap, and PL properties of the films. It is concluded that growth temperature predominates the PL behavior of ZnO films. We also discussed the physical mechanism of affecting PL behavior.II ZnO thin films with strong c-axis orientation have been successfully deposited on Si(100) substrate at 750℃ by using reactive RF magnetron sputtering. The influence of annealing temperature ranging from 600 to 1000℃ on the microstructure and PL properties of ZnO films was investigated by XRD, TEM and PL measurement at RT. The XRD and TEM results show that the grain size of ZnO film increases and the residual stress in the film is tensile about 1 GPa with the increase of annealing temperature below 900℃. After annealed at 1000℃, the grain size decreases and the residual stress in the film changes into compressive about -2 GPa. The PL spectra of the ZnO films displayed two emission bands, ultraviolet (UV) exciton transition and visible defect photoluminescence. The intensity of UV PL spectrum and the...