【作者】 朱慧超；

【导师】 杜国同；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 ZnO是一种具有压电和光电特性的直接宽带隙半导体材料,是人们关注的短波长光电材料的新焦点。其具有高的激子束缚能(60meV),极好的抗辐照性能和化学稳定性能,低的外延生长温度和大尺寸衬底材料等一些独特的优点,有望用于制备UV发光二极管和低阈值激光器。本论文即采用MOCVD技术,在n-Si、n-InP衬底上生长ZnO薄膜,研究了外延生长过程中生长温度和气体流量对ZnO薄膜结构性质、表面形貌和光学性质的影响,同时采用生长薄膜后热处理的方法,通过热扩散使衬底中含有的V族元素进入ZnO薄膜中,取代O元素或者占据O空位成为受主,从而成功制备出p-ZnO薄膜,我们利用XPS技术已经证实了P元素在ZnO薄膜中的存在。我们利用真空蒸发技术制备了金属点状电极,并且研究了n-Si/p-ZnO异质结的整流特性。实验发现,生长温度对ZnO薄膜的结构、表面形貌和光学质量有重要的影响:不同温度下生长的样品,在610°C生长样品的(002)峰最强,薄膜晶粒尺寸较大,说明在此温度下生长的薄膜质量最好。氧气流量对ZnO薄膜的晶体结构、表面形貌和表面形貌有显著影响:当氧气流量为180sccm时,样品只出现ZnO(002)面的衍射峰,且峰强度最强,薄膜晶粒较大;当氧气流量超过180sccm时,随着其流量的增加,(002)衍射峰和其他峰强度逐渐减弱。氮气流量对ZnO薄膜的晶体结构、表面形貌和光学特性有显著影响:实验发现,最佳的流量为600sccm。通过对样品的XRD谱的比较可知,当氮气流量超过600sccm时ZnO(002)衍射峰强度降低,半高宽增大,薄膜的晶体质量显著降低。我们首次采用MOCVD生长技术,在n-Si衬底上通过P元素热扩散的方法制备出p-ZnO薄膜。采用X光电子能谱仪(XPS)分析了P在ZnO薄膜中的存在状态,结果表明,随着刻蚀深度的增大,P元素的含量有所提高,许多P原子取代O的格点位置,作为受主存在,使得薄膜转为p型。通过重复实验我们发现,热扩散是改变薄膜电导类型的关键原因。高温改善了薄膜的结晶质量,减少了晶粒间界原子所占的比例,使存在于晶粒间界的P原子扩散入晶体内部而占据O的位置,从而使薄膜变为p型。我们首次采用MOCVD外延生长技术,在掺杂不同元素(磷,砷,锑)的三种n-Si衬底上生长ZnO薄膜成功地制作了n-Si/p-ZnO/n-ZnO发光器件并分析了电致发光特性。所有n-Si/p-ZnO/n-ZnO异质结都表现出典型的整流特性,正向开启电压大约为2V,反向电流随反向偏压线性增加。在达到一定的正向电流时,器件发出白色的光芒,我们记录并分析发光主要是由于电子和深受主能级辐射复合。我们首次采用MOCVD技术在两种n-InP衬底上观察到n-InP/p-ZnO/n-ZnO异质结的电注入发光,并分析了其发光特性。同样的,由于衬底中含有大量的P元素可于通过热扩散进入ZnO薄膜中取代O元素或者O空位成为受主,从而使靠近衬底的ZnO薄膜成为p型,而远离衬底的ZnO薄膜仍为n型,这样我们就得到了n-InP/p-ZnO/n-ZnO异质结构。我们测试了n-InP/p-ZnO/n-ZnO异质结的电致发光特性。发光在可见光区,它与我们所期待的紫外发光相比,出现了红移,我们认为这是p-ZnO层的载流子浓度很低的缘故,或者是因为薄膜中存在部分缺陷使得注入的电子在经过势垒层到达p-ZnO区时容易与价带深能级发生辐射复合。更多还原

【Abstract】 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.更多还原