【作者】 戴丽萍；

【导师】 邓宏；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2008， 博士

【摘要】 ZnO是一种直接宽禁带半导体材料,室温禁带宽度为3.37 eV,激子束缚能高达60 meV。因此可以实现室温下的高效率激子发射以及紫外发光,使得ZnO成为一种极具发展和应用潜力的半导体材料,有望在不久的将来取代Ⅲ-Ⅴ族半导体材料,在短波长发光二极管、激光器等领域得到广泛的应用。要实现ZnO基光电器件的应用,首先必须获得高质量稳定p型ZnO薄膜,其次是要提高ZnO的发光效率。而ZnO因其本征缺陷而天然呈n型导电特性,导致高质量稳定p型ZnO薄膜的制备非常困难,这是ZnO研究中面临的主要挑战:此外,一般方法制备的ZnO薄膜大多呈极性c面生长,而极性ZnO由于强压电场效应往往导致发光效率较低,因此沿非极性和半极性面生长的ZnO薄膜通过抑制或减弱压电场,可望提高其发光效率。本文针对以上这两点作了有益的探索性的研究:采用一种单源化学气相沉积（SSCVD）技术,在n-Si（100）衬底上制备非极性面（100）择优取向ZnO薄膜,对其微结构、生长机理和光电性质进行了深入的研究;制备基于非极性面择优取向的p型ZnO薄膜,首次从实验和理论的角度探讨了p型ZnO薄膜的稳定性与其织构取向的关系。论文的主要内容和创新性结果如下:1.制备出一种适合SSCVD技术沉积ZnO薄膜的新型单一固相源,采用傅立叶变换红外光谱和热重分析等手段对其结构和性质进行了研究。确定其化学式（Zn₄（OH）₂（O₂ CCH₃）₆·2H₂O）及热分解温度（210℃）。选择适当的条件热分解固相源沉积薄膜,薄膜的红外透射谱及光电子能谱测试表明该固相源适合SSCVD技术制备ZnO薄膜。2.基于SSCVD技术制备非极性面（100）择优取向ZnO薄膜,研究各工艺参数（源温、衬底温度、热退火温度以及沉积压强）对其微结构的影响。实验发现源温、衬底温度、热退火温度影响薄膜的非极性面择优取向度和结晶质量,结果表明源温为220℃、衬底温度为400～450℃、退火温度为600～700℃时,薄膜结晶质量较好;沉积压强则影响薄膜成分的化学配比,在一定压强下（20～60Pa）获得了富氧的薄膜。通过对各工艺参数的控制,制备随机取向和极性c面取向的ZnO薄膜,对照c面取向出现的条件,探讨了所制备的非极性面择优取向ZnO薄膜的生长机理,首次从实验的角度证明了这种非极性面择优取向薄膜的生长基于单固相源在一定条件下分解的多聚ZnO单体沉积,当这种多聚ZnO沉积单体被破坏时,可获得随机取向和极性c面取向的ZnO薄膜。3.研究了不同激发条件、不同退火温度、不同环境温度及压强对非极性面择优取向系列ZnO薄膜的光致发光影响。实验发现选择适当的荧光激发波长时,有利于从薄膜的PL谱中获得其结构质量等信息;其它条件一定,当热退火温度为700℃时,有利于薄膜的紫外发射峰的增强同时抑制其缺陷峰,表面薄膜结晶质量较好;通过He-Cd激光激发的PL谱探讨了不同环境温度和压强对富氧具有V_Zn（锌空位）的ZnO薄膜紫外光致发光的影响,发现薄膜的紫外发光强度随温度的升高而降低,而发光峰位则随之红移;环境真空度的降低有利于薄膜紫外发光的增强;通过与极性c面取向、非极性面择优取向的富锌的ZnO薄膜的光致发光强度的比较,发现非极性面择优取向的富氧ZnO:V_Zn薄膜有强紫外光发射现象;薄膜的透射谱表明其良好的结晶质量;飞秒激光激发的PL表明这种ZnO:V_Zn薄膜同时还具有非线性光学即双光子吸收现象。4.研究了沉积压强和衬底温度对ZnO薄膜的电学性质的影响规律。霍尔测试结果表明在20～60Pa的压强、衬底温度为400～500℃的条件下,在不掺杂下获得了p型ZnO薄膜。研究发现ZnO薄膜中化学成分配比偏离,即具有V_Zn的ZnO薄膜,化学计量比值的大小对其电学性质影响较大;并从点缺陷的平衡理论的角度对本征ZnO的p、n型导电特性机理进行分析。在获得稳定p型ZnO薄膜的基础上,制备了p-ZnO:V_Zn/n-ZnO:Al同质p-n结,该结的Ⅰ-Ⅴ特性曲线表明其具有明显的电流整流特性。5.基于第一性原理计算,从理论的角度探讨了非极性面（100）ZnO:V_Zn的电子结构及光学性质。通过与ZnO晶体的电子结构及光学性质对比研究,发现（100）ZnO:V_Zn具有p型导电特性及强紫外光吸收及发射等特性,这与实验发现的非极性面（100）择优取向ZnO:V_Zn薄膜具有p型导电特性和强紫外光发射等现象相符合。6.研究了基于非极性面择优取向的掺N的p型ZnO薄膜的稳定性与其织构取向的关系。采用后处理和原位双源方法进行N掺杂,制备非极性面取向和极性c面取向的p型ZnO薄膜,发现了非极性择优取向ZnO薄膜具有更好的p型稳定性。首次从薄膜的内建电场和电子结构的理论计算等角度对两种织构取向的p型薄膜的稳定性进行比较和分析,结果表明p型ZnO薄膜与其织构取向有关,非极性面取向结构有利于p型ZnO薄膜电学性能的稳定。更多还原

【Abstract】 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 substituteⅢ-Ⅴmaterial 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,itsⅠ-Ⅴcurve 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.更多还原