Preparation And Optoelectronic Properties Of ZnO Thin Films By Single Source Chemical Vapor Deposition

ZnO is an optoelectronic semiconductor material with a direct wide-band of 3.37eV and a high exciton binding energy of 60meV at room temperature.It can realize efficient excitonic emission and UV emission at room temperature.Rencently,ZnO has been considered as a potential semiconductor material with promising applications to substituteâ…¢-â…¤material in shortwave length light-emitting diodes and lasers.To realize ZnO-based optoelectronic device applications,there are two imperative issues need to be solved,one is to fabricate high-quality p-type ZnO films,the other is to obtained the efficient luminescence.While ZnO is naturally n-type conductivity due to the native defects of oxygen vecancy,which is the difficulty in achieving high-quality stable p-type ZnO thin films,and is the greatest challenge in expoiting ZnO. Furthermore,the ZnO films fabricated by most deposition technique are usually with polar c-plane orientation.Polar ZnO is always with low luminescence efficiency for its strong piezoelectric field.Thus nonpolar and semi-polar plane orientation ZnO films can restrain or weaken piezoelectric field and improve luminescence efficiency.In this work,we mainly concern on the above two issues and make some useful researches for them:The preferential nonpolar(100) plane orientation ZnO thin films were fabricated by single source chemical vapour deposition(SSCVD) technique.The microstructure, growth mechanism and opto-electronic properties were investgated.And preferential nonpolar(100) plane orientation p-type ZnO thin films were also deposited on n-Si(100) substrate.The relationship of its stability and structural orientation was first studied by experimental anlysis and theoretical calculation.The detailed contents and innovations of the dissertation are as follows:1.A novel single solid organic zinc fountain precursor was synthesized.ZnO thin films were prepared by SSCVD with the precursor.The Fourier transform infrared (FTIR) spectra analysis revealed that precursor formula can be described as Zn₄(OH)₂(O₂CCH₃)₆·2H₂O.And thermogravimetric analysis(TGA) demonstrated that it could decompose at low temperature(210℃).X-ray photoelectron spectra and FTIR analysis of ZnO thin films by precursor thermo-decomposing provided the evidence that solid organic zinc fountain can be employed for preparing ZnO thin films by SSCVD2.Preferential nonpolar plane(100) orientation ZnO thin films were fabricated by SSCVD technique.The influence of deposition parameters(precursor,substrate, annealing temperature and the chamber atmosphere pressure) on the microstructure of the films were studied.Found that the deposition parameters mentioned can take an effect on the preferential orientation degree and the crystal quality of the films.The results demonstrated the films were with good quality at precursor temperature(220℃), substrate temperature(400～450℃) and annealing temperature(600～700℃).And the effects of chamber atmosphere pressure on O/Zn atomic ratio of the films were studies. It was found that the films deposited at the pressure of 20～60Pa were with excess oxygen.The random orientation and polar e plane ZnO thin films were also fabricated by controlling deposition parameters.Compared to the growth condition of the preferential nonpolar plane orientation ZnO thin films,the mechanism of the growth of the preferential nonpolar plane orientation ZnO thin films were studied and first proved to originating from the poly-ZnO molecule deposition unit decomposed by the single solid precursor.Hence,when the poly-ZnO molecule deposition unit was destroyed,the random orientation and polar c plane ZnO thin films can be obtained.3.The influence of different exciton light source,different annealing temperature of the film,different temperature and atmosphere pressure of experiment on the photoluminescenee(PL) properties were also studied.Found it was better for the fluorescence PL spectra of ZnO films showing the information of its structure and crystal quality if with appropriate exciton light wavelength.And the Ultrovioliet(UV) emission can be enhanced and emission correlative to defect can be restrained when the films annealed at 700℃,which demonstrated the film with high quality.The intensifies and energy of UV emission of the V_Zn(zinc vacancy)film with excess oxygen varied with the temperature and atmosphere environment were investigated by UV PL excited by He-Cd laser.The intensities and energy of which decreased with the temperature increased.It was also found that intense UV emission of the film in atmosphere environment but weak in vacuum.Contrasted to the UV PL of the polar c plane and preferential nonpolar plane orientation but with deficiency oxygen ZnO thin films,the preferential nonpolar plane orientation with excess oxygen ZnO thin films showed the strongest UV emission.Its transmittance spectra showed the film with high crystal quality.And its femo-laser PL demonstrated that the films were with nonlinear optics properties of double photon absorbed.4.The electrical properties of the films fabricated at the conditions of different chamber pressures and substrate temperatures were studies in detail.Hall-effect measurements demonstrated that the native p-type ZnO films(ZnO:V_Zn) were obtained at the conditions of chamber pressure(20～60Pa),substrate temperature(400～500℃). At the same time,O/Zn atomic ratio of the films was found to affect the electronic properties.The p,n-type conduction mechanisms of the native ZnO films were also proved by defects equibrium theory in this thesis.Based on the p-type ZnO thin film obtained,p-ZnO:V_Zn/n-ZnO:A1 p-n homo-junction was fabricated,itsâ… -â…¤curve exhibited the p-n homo-junction with an evident rectifying characteristics.5.Based on the first principle stimulation,the electronic structures and optical properties of the(100) ZnO:Vzn studied by theoretical analysis demonstrated it possesed p-type condution and trong UV absorbance and emission compared to that of the ZnO crystal.These were consistent to the experimental results on preferential nonpolar(100) plane orientation ZnO:V_zn thin films.6.Preferential nonpolar plane and polar c plane orientation p-type ZnO thin films were fabricated by the N doping methods of heat treatment subsequently and double-sources in situ respectively.The relationship of the stability and structural orientation of preferential nonpolar plane orientation N doped p-type ZnO thin film was studied.The electronic properties of them exhibited the former was more stable than the latter,the phenomenon was first analyzed and proved by the internal-developing electronic field mode and the electronic structure theoretical calculation of two kinds orientation of p-type ZnO.And the results demonstrated that the stability of the p-type ZnO thin film was correlative to its structural orientation,the structure of preferential nonpolar plane orientation would favor the stability of the p-type ZnO thin film.