【作者】 杨天鹏；

【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， 2009， 博士

【摘要】 氧化锌(ZnO)材料,是直接带隙的宽禁带半导体材料,禁带宽度达3.37eV,它在室温下有高达60emV的激子束缚能,正是由于具有这些优异的性质,使得近年来ZnO材料得到了人们的广泛关注。本论文利用新型等离子体辅助金属有机化学气相沉积系统(plasma-assisted MOCVD)在蓝宝石衬底、Si衬底和GaN外延层上生长出高质量的ZnO薄膜,同时利用N2O作为掺杂源进行了p型掺杂的研究,得到了p型ZnO薄膜,并以此为基础制作了相关的原型光电器件。研究内容如下:1、根据MOCVD生长ZnO薄膜的原理及技术要求,参与设计和组装了新型等离子体辅助MOCVD系统,该系统设计具有自主知识产权,已取得国家发明专利。2、利用MOCVD在蓝宝石衬底和Si衬底上生长出高质量的ZnO薄膜。通过优化生长条件和引入分步退火生长的方法,在c面蓝宝石单晶衬底上得到了高质量ZnO薄膜,其(002)面X射线衍射(XRD)半峰宽(FWHM)为0.1699°,可见光透过率超过90%,原子力显微镜(AFM)测试得到的薄膜表面均方根粗糙度最小为4.696nm;而在Si衬底上生长的ZnO(002)面的衍射峰半峰宽最窄为0.1602°;在蓝宝石和Si衬底上生长的ZnO薄膜的光荧光(PL)谱的近带边紫外发射与深能级发射的强度比最大为433:1和327:1,此结果为世界上已知报道的MOCVD法生长ZnO薄膜的最好结果。3、利用射频离化的N2O等离子体对ZnO进行了掺杂。在c面蓝宝石和Si衬底上都得到了p型ZnO薄膜。在c面蓝宝石衬底上生长的p型ZnO薄膜经Hall方法测量得到的最好结果是电阻率8.71Ω?cm、迁移率2.09 cm2/V?s、载流子浓度3.44×1017 cm-3,这是首次以N2O等离子体作为掺杂源,利用MOCVD方法生长出高质量的p型ZnO薄膜。同时利用n型Si衬底生长出p型ZnO,制备了p-ZnO/n-Si异质结构器件,其I-V曲线表现出良好的整流特性和光电响应特性,之前未见相关报道。4、先利用路明集团的工业化MOCVD系统在c面蓝宝石衬底上生长出p型GaN外延层,然后在p-GaN外延层上生长了n型ZnO薄膜,并制作出n-ZnO/p-GaN异质结发光二极管原型器件,在室温下器件电致发光(EL)的主发光峰在415nm左右,经高斯拟合发现这个主发光峰由中心位置在410nm和470nm的两个发光峰组成,这两个发光峰归结于n-ZnO/p-GaN异质结两侧的n-ZnO和p-GaN层中均产生辐射复合的缘故。MOCVD法生长的n-ZnO/p-GaN异质结发光二极管原型器件和发现此异质结器件在电致发光过程中n-ZnO和p-GaN层中均产生辐射复合发光,这些都为国内外首次报道。本论文的创新点:1、利用分步退火生长方法,大幅提高了所生长的ZnO薄膜晶体质量,在蓝宝石和Si衬底上生长的ZnO样品的(002)面的XRD半峰宽低至0.1699°和0.1602°;2、利用新型等离子体辅助MOCVD设备,采用射频离化的N2O等离子体作为掺杂源对ZnO薄膜生长时进行掺杂,在国内外首次通过这种掺杂生长方法得到了高质量的p型ZnO薄膜;3、在n型Si衬底上生长出p型ZnO薄膜,并制作了p-ZnO/n-Si异质结构器件,其I-V曲线表现出良好的整流特性和光电响应特性,证明了掺杂的ZnO薄膜具有很好的p型特性,之前未见相关报道;4、利用路明集团的工业化MOCVD系统先在c面蓝宝石衬底上生长出p型GaN外延层,然后在p-GaN外延层上生长了n型ZnO薄膜,并制作出n-ZnO/p-GaN异质结发光二极管原型器件,在室温下器件EL的主发光峰在415nm左右,经高斯拟合发现这个主发光峰由中心位置在410nm和470nm的两个发光峰组成,这两个发光峰归结于n-ZnO/p-GaN异质结两侧的n-ZnO和p-GaN层中均产生辐射复合的缘故。这是国内外首次报道用MOCVD法生长出n-ZnO/p-GaN异质结发光二极管原型器件并首次发现此异质结器件在电致发光过程中n-ZnO和p-GaN层中均产生辐射复合发光。更多还原

【Abstract】 ZnO, a wide direct-gap semiconductor material, has attracted great interest recently because of its wide band-gap (3.37eV) and relatively large exciton binding energy (60meV) at room temperature (RT) and the production cost will be reduced significantly compared with current technology. It has been regarded as one of the most promising candidates for the next generation of short-wavelength light emitting diodes (LEDs) and lasing devices (LDs). Especially in 1996, the upsurge in ZnO research is coming due to the realization of the light pumped exciton emitting. ZnO can be used to fabricate emitting diode, ultraviolet detector, surface acoustic wave device, transparent electrode, thin film transistor, gas sensor and nano structure device. In order to realize the above-mentioned devices, it is necessary to grow high quality ZnO film and p type ZnO film by proper doping. A lot of methods have been used to grow ZnO films such as Sputtering, Pulsed Laser Deposition (PLD), Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapor Deposition (MOCVD). Among them, MOCVD offers the advantage of industrial production, such as high growth rate and efficiency, large area uniformity, prefect composition control and sharp interface. In this thesis, we grow high quality ZnO film on sapphire, silicon and gallium nitride epi-layer by new-type self-designed plasma-assisted MOCVD, and find a way of p type doping by using N2O plasma source. Then we fabricate p-ZnO/n-Si and p-GaN/n-ZnO heterojunction devices based on high quality p and n type ZnO.ZnO thin films had been grown in sapphire firstly by using MOCVD system. According to the growth temperature and O2 flow rate on ZnO films characteristics, we get the optimized growth condition. Temperature is the most crucial factor in the ZnO film growth, and proper growth temperature is in favor of the grains merger and the formation of thin films. As the growth temperature of 550℃and the O2 flow rate of 200~300sccm, ZnO sample has the best crystal quality, surface morphology and optical quality. For ZnO grown on c-sapphire, the FWHM of (002) X-ray diffraction peak was 0.187°, transmission ratio was more than 90%, and the intensity ratio of PL near band edge UV emission and deep level emission was as large as 433:1,which was the world’s best results reported.We study the step-by-step annealing growth of ZnO films on c-sapphire. Step-by-step annealing growth was, after a period of growth time, ZnO film growth was suspended, and ZnO was experienced a period of annealing, then growth was restored. The quality of ZnO films has been further improved by step-by-step annealing growth, the FWHM of (002) X-ray diffraction peak was as narrow as 0.1699°, and the smallest RMS (root mean square) roughness measured by AFM (atomic force microscope) was down to 4.696nm. Compare with the samples under normal growth, ZnO samples under step-by-step annealing growth has better crystal quality and optical quality.Based on the growth condition of ZnO films on c-sapphire, we study the N-doping condition of ZnO films using RF ionized N2O plasma. Only at the right flow and temperature condition high quality p type ZnO samples can be made. Temperature is also the most crucial factor in the p-ZnO film growth. Best p type ZnO thin film had been grown at 430℃on c-sapphire with the resistivity of 8.71Ω?cm, hole mobility of 2.09 cm2/V?s and hole concentration of 3.44×1017 cm-3. XPS (X-ray Photoelectron Spectroscopy) was used to analyze the chemical composition of ZnO film. The XPS data proved that N-Zn bond exist in the film. All results show that N2O plasma is a high efficient source of N doping.With reference to the growth and doping conditions of ZnO films on c-sapphire, we also study growth and doping of ZnO films on (001) Si substrates. High quality undoped and N-doped p type ZnO films have been made on Si substrates, and we fabricate p-ZnO/n-Si heterojunction device. For ZnO grown on Si substrates, the FWHM of (002) diffraction peak was as narrow as 0.1602°, the intensity ratio of PL near band edge UV emission and deep level emission was as large as 327:1, which was the world’s best results reported about ZnO films grown on Si substrates. The p-ZnO/n-Si heterojunction device showed that the device has good characteristics of the diode rectifier and photoelectric response characteristics. Turn-on voltage of devices was about 4.7V, at reverse voltage of-6V there is no significant increase in the reverse current. When there was light, reverse current increase in the device under the same reverse voltage, which clearly showed that the device has good photoelectric response characteristics.Using both Luming group’s industrialized MOCVD system and our independent intellectual property rights MOCVD system, n-ZnO/p-GaN heterojunction light emitting diode was grown on (0001) sapphire substrate. An Mg doped GaN layer with a hole concentration of ~1017 cm-3 was used for the p-type side, and a unintentionally doped n-type ZnO layer with an electron concentration of ~1018 cm-3 for the n-type side of the heterojunction device. Distinct blue-violet electroluminescence emission with a dominant emission peak at ~ 415 nm was observed at room temperature. The origins of the EL emissions are discussed in comparison with the photoluminescence spectra,and it was supposed to be attributed to a radiative recombination in both n-ZnO and p-GaN layers. These results represent meaningful steps for developing ZnO-based optoelectronics devices. It is the first report of n-ZnO/p-GaN heterojunction LED grown by MOCVD and the phenomenon about radiative recombination in both n-ZnO and p-GaN layers.更多还原