Preparation And Investigation Of P-ZnO Film And ZnO Light Emitting Device

As anâ…¡-â…¥group semiconductor,ZnO has attracted great interest for its wide band gap (3.37eV) and relatively large exciton binding energy(60meV) at room temperature(RT).It has been regarded as one of the most promising candidates for the next generation of ultraviolet(UV) light-emitting diode(LED) and lasing diode(LD) operating at high temperatures and in harsh environments.Since the first report of realization of lasing emission at RT by the scientists at 1996,ZnO has become a focus in the field of optoelectronic technology.However,the realization of stable and reproducible p-type ZnO has long been the bottleneck of ZnO-base optoelectronic devices.Many researchers have managed to dope p-ZnO and fabricate ZnO based homojunction LED,while the report on effective ZnO light emitting devices is still limited.It is necessary to improve the qualities of ZnO light emitting devices to explore the advantages of ZnO material.In this thesis,many research works are conducted to fabricae high quality native ZnO, p-ZnO film and ZnO based short wavelength LED.Metal-organic Chemical Vapor deposition (MOCVD) technique is used to deposite native and p-ZnO film on different substrates,such as GaAs,Si,and sapphire.Furthermore,the properties of ZnO LED are investigated.ZnO homojunction light-emitting diode with n-ZnO/p-ZnO:As/GaAs structure is produced by MOCVD on p-GaAs substrate,p-type ZnO:As film is obtained out of thermal diffusion of arsenic from GaAs substrate with subsequent thermal annealing.The hole concentration reached 10¹⁸/cm³.Desirable rectifying behavior is observed from the current-voltage curve of the ZnO p-n homojunction.Furthermore,two distinct electroluminescence bands centered at 3.2eV and 2.5 eV are observed from the junction under forward bias at room temperature.Among many dopoing methods,diffusion doping technique is comparatively easy to conduct.In addition,p-GaAs wafer has several fundamental advantages for fabricating ZnO-based LED and LD,such as its conductivity and cleavability.ZnO homojunction LED is fabricated on Si(100) substrate by plasma assisted MOCVD. The p-type ZnO:N layer is formed using radical N₂O as the nitrogen precursor.The N₂O is activated by a FR souce.The device exhibits desirable rectifying behaviour with a turn-on voltage of 3.3V and a reverse breakdown voltage higher than 6 V.Distinct electroluminescence emissions centred at 3.14eV and 2.5eV are detected from this device at forward current higher than 20mA at room temperature.Among many substrates,Si is especially attractive due to the well-known advantages such as low cost,conductive,easy to cleave and wellmatured technology,as well as its potential application in Si-based optoelectronic integrated circuits.A novel annealing technique to realize effective p-type ZnO:N has been developed.The reproducible p-type ZnO:N layer is formed with NH₃ as N doping source followed by thermal annealing in N₂O plasma protective ambient.Based on the p-ZnO:N film,ZnO homojunction LED with is fabricated on c-plane sapphire substrate.The device exhibited desirable rectifying behavior.Distinct electroluminescence emission centered at 3.2eV and 2.4eV are detected from this device.The ultraviolet emission is comparable to the visible emission in the electroluminescence spectrum.Furthermore,the realization of ultraviolet electroluminescence from ZnO LED fabricated by MOCVD technique paves the way for future industrialization.ZnO film is deposited on c-plane sapphire substrate.The etching treatments for as-grown ZnO film is performed in NH₄Cl aqueous solution as a function of NH₄Cl concentration and etching time.It is found that NH₄Cl solution is an appropriate candidate for ZnO wet etching because of its controllable and moderate etching rate.The influence of etching treatments on the morphology and optical properties of ZnO film has also been investigated.Wet etching technique has many fundamental advantages in fabricating semiconductor devices,such as its low cost and simpleness.