Growth Of ZnO Films On Si And InP Substrates And Fabrication Of ZnO Based Light Emitting Devices By MOCVD

Title: Growth of ZnO films on Si and InP substrates and fabrication of ZnO based light emitting devices by MOCVDMajor: Micro-electronics and solid-electronics Tutor: Prof. Guotong DuWith the fast developing information technology, communication and network which are depended on optoelectronics and microelectronics becomes the core of new technology. Short wavelength LEDs and LDs have great uses in light memory, display and laser print, etc. ZnO films attract much more attention as ZnSe and GaN in optoelectronics research field. ZnO, as a promising wide direct-gap II-VI semiconductor, has remarkable optical and electrical characteristics, and use in domain semiconductor illumination. It can also be used in sensors, piezoelectric transducers, transparent conductor, surface acoustic wave devices, and lasers. There are lots of methods have been used to deposit ZnO films such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), atomic layer epitaxy (ALE), sputtering, chemical vapor deposition(CVD), e-beam evaporation, sol-gel, spray pyrolysis.In this thesis, we prepare ZnO films on Si and InP substrates by MOCVD. Simultaneously, we investigate thoroughly the influence of the growth temperature and flow rate of O2 and N2 on the properties of the films, and successfully prepare p-ZnO thin film by P diffusion from n-Si(P doped) substrate. The heterojunction of n-Si/p-ZnO, n-Si/p-ZnO/n-ZnO and n-InP/p-ZnO/n-ZnO are fabricated and their characteristics are investigated.ZnO films are grown by MOCVD on Si substrates. The effects of the growth temperature on the properties of the films are analyzed and the optimized growth conditions are obtained. The results show that the ZnO film deposited at 610°C has the best cry stall inity, surface morphology and the biggest grain size. Increasing the growth temperature, the growth speed of ZnO films was increased. Under low temperature, it depends on the surface reactive velocity. When the temperature is moderate, it is affected by the quality transport of the source. Under higher temperature, because ZnO films decomposed, the speed decreases with the increasing of the temperature.It was found that the flow rate of O2 strongly influenced on the structural properties and surface morphology of ZnO films. The film grown at 180sccm had only one intense (002) diffraction, and had the biggest grain size. Increasing the flow rate of O2, the intense of (002) and other diffraction were decreased, when it reaches 260sccm, the crystalline quality of the ZnO films was degraded to polycrystal.The flow rate of N2 strongly influenced on the structural and optical properties of the ZnO thin films. The optimized flow rate of N2 is 600sccm. Increasing the flow rate of N2, the intense of (002) and other diffraction were decreased, when it reaches 1200sccm, the crystalline quality of the ZnO films was degraded to polycrystal.The ultraviolet emission in ZnO epilayer enhanced obviously after annealed, so annealing can improve the quality of ZnO films.The p-ZnO films are firstly prepared by MOCVD through P diffusion from P-doped n-Si substrates. After annealing, P atoms substitute O lattice bonded with Zn atoms, acted as acceptors, so films present p-type conduction. So n-Si/p-ZnO heterojunctions are fabricated by MOCVD. Ohmic contacts to p-ZnO are made by applying AuZn dots by evaporating, and to the n-Si by evaporating of Al. Rectifying behaviors are observed in all heterjunctions. The forward turn-on voltage is about 3V, the reverse current increases lightly with the increase of the reverse bias voltage.The n-Si/p-ZnO/n-ZnO light emitting devices are firstly fabricated by MOCVD deposition ZnO on different n-Si substrates through thermal annealing. Different V-group elements P, As and Sb can diffuse in ZnO films. Ohmic contacts to the ZnO and n-Si are made by evaporating AuZn and Al. All of the n-Si/p-ZnO/n-ZnO heterjunction exhibit typical rectifying behavior. Under forward bias the device produces weak white EL covering from 400nm to 600nm. By comparing the EL spectrum of our LED with the PL spectra of the individual heterostructure layer it can be concluded that the blue EL emission emerges from the ZnO region of the device due to the defects or low hole concentration in it.The n-InP/p-ZnO/n-ZnO light emitting devices are firstly fabricated by MOCVD deposition ZnO on n-InP substrates because P element from substrates can diffuse in ZnO. Ohmic contacts to the ZnO and n-InP are made by evaporating AuZn and Al. All of the n-InP/p-ZnO/n-ZnO heterjunction exhibit typical rectifying behavior. The turn-on voltage is ~3V. Under forward bias the device produces weak white EL covering from 400nm to 600nm. By comparing the EL spectrum of our LED with the PL spectra of the individual hetero structure layer it can be concluded that the white EL emission emerges from the ZnO region of the device due to the defects or low hole concentration in it.