【作者】 孙景昌；

【导师】 杜国同；

【作者基本信息】 大连理工大学 ， 微电子学与固体电子学， 2009， 博士

【摘要】 氧化锌（ZnO）是一种直接带隙宽禁带半导体材料,室温下禁带宽度为3.37 eV、激子束缚能高达60 meV,这使ZnO材料有望在短波长高效率光电器件领域内发挥重大作用。自从1996年日本和香港的科学家首次实现了ZnO薄膜的室温下光泵浦紫外激射以来,ZnO材料已经成为光电子领域中的研究热点。目前,ZnO发光器件的效率较低,ZnO同质结发光二极管（LED）、激光二极管（LD）仍未达到实用化的水平,其中一个重要原因是由于稳定、高质量、可重复的p-ZnO薄膜的制备尚有一定难度。本论文针对以上这个热点也是难点的问题,在p-ZnO掺杂和ZnO同质结LED制备方面开展了一系列研究工作。利用金属有机物化学气相沉积（MOCVD）技术,在多种衬底（GaAs、Si和蓝宝石）上制备了高质量的p-ZnO薄膜和ZnO同质结LED。利用多种表征手段对ZnO薄膜和器件进行了深入的研究。具体研究内容如下:首次通过扩散掺杂方法,在p-GaAs衬底上制备出具有紫外电致发光特性的ZnO同质结LED。首先通过优化实验条件的方法在GaAs衬底上制备出高质量ZnO薄膜,然后将ZnO薄膜在适当温度下进行退火处理,使GaAs衬底中的As扩散到ZnO薄膜中从而制备出As掺杂的p-ZnO（p-ZnO:As）薄膜,p-ZnO:As的空穴浓度最高可达-10¹⁸/cm³。在p-ZnO:As薄膜的基础上制备出了具有n-ZnO/p-ZnO:As/p-GaAs结构的ZnO同质结LED。该器件表现出了优异的整流特性,室温下可观测到明亮的电致发光。该器件电致发光谱中呈现出一个位于3.2eV附近的紫外发光峰和一个位于2.5eV附近的可见发光峰。相比于其他掺杂技术,扩散掺杂方法简单易行,而且p-GaAs衬底而具有良好的导电性和解理性,这为ZnO光电器件的制备提供了极大方便。利用等离子辅助MOCVD设备将笑气（N₂O）离化作为N源制备出N掺杂的p-ZnO（p-ZnO:N）薄膜,并在此基础上制备出具有n-ZnO/p-ZnO:N/Si结构的ZnO同质结LED。该器件表现出良好了p-n结整流特性,其电致发光光谱中呈现出两个发光峰,一个是位于3.14eV附近的较弱的紫外发光峰,另一个是位于2.5eV附近的强烈的可见发光峰。在众多的衬底材料中Si具有明显的优势,比如成本低廉、易于解理、具有很好的电导和热导性能、适合大规模集成工艺等特点,因此在Si衬底上制备ZnO同质结LED有着广阔的应用前景。原创性地开发了N₂O等离子保护退火工艺,实现了高质量p-ZnO:N薄膜的制备。首先利用氨气（NH₃）作为N掺杂源制备出ZnO:N薄膜,然后将ZnO:N薄膜进行高温退火处理。为了在一定程度上抑制高温下ZnO:N薄膜中O和N的分解,采用经射频发生器离化的N₂O作为ZnO:N薄膜的退火保护气体。通过这个技术制备出了质量较高的p型ZnO:N薄膜,其空穴浓度达到1.29×10¹⁷/cm³。在此基础上制备出以蓝宝石为衬底的ZnO同质结LED,该器件表现出了优异的p-n结整流特性,其电致发光谱中出现了一个位于3.2eV附近的紫外发光峰和一个位于2.4eV附近的可见发光峰。值得注意的是,在大部分关于蓝宝石衬底上制备的ZnO同质结LED电致发光的报道中,电致发光谱中可见光的发射往往占据绝对优势,然而在我们的结果中紫外光的发射强度几乎和可见光的发射强度相同。蓝宝石是目前工业中短波长发光器件的主要衬底,MOCVD又是规模制备发光器件的主要设备,所以利用MOCVD设备在蓝宝石衬底上制备ZnO同质结LED有着很强的市场潜力。利用强酸弱碱盐氯化铵（NH₄Cl）的水溶液成功地实现了ZnO薄膜的可控湿法刻蚀,并且研究了刻蚀对ZnO薄膜形貌和光学性质的影响。实验中利用不同浓度的NH₄Cl的水溶液,对ZnO薄膜进行了湿法刻蚀。结果显示,刻蚀的深度与刻蚀的时间成线性关系,刻蚀的速率与溶液的浓度也成线性关系,这就意味着可以通过控制刻蚀时间和溶液浓度来控制刻蚀深度和刻蚀速率,从而实现ZnO薄膜的可控刻蚀。湿法刻蚀技术简单易行、成本低廉。可控湿法刻蚀的实现为ZnO光电器件制备奠定了良好的工艺基础。更多还原

【Abstract】 As anⅡ-Ⅵgroup 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.更多还原