选择性横向外延生长半极性面GaN材料及器件光电性质研究

发布时间：2018-05-31 02:29

本文选题：选择性横向外延生长 + 半极性面GaN材料与器件　；参考：《南京大学》2016年博士论文

【摘要】：Ⅲ族氮化物材料带隙从0.7 eV到6.2 eV连续变化,波长覆盖了从近红外到紫外极为宽广的光谱范围,具有优异的光电特性,具有比其他材料更大的应用范围和更高的发光效率。这些优点使氮化物LED成为目前最成功的近紫外到蓝绿光的发光器件。然而氮化物异质结构是强极化、高应变的量子体系,极化不连续性引入极强内建电场,导致量子阱结构中电子空穴波函数的空间分离,降低了发光效率。趋向于无极化的研究思路,非极性面和半极性面的GaN基LED的研究逐渐得到重视,其中极化效应的减弱会带来更加优异的光电特性和巨大的潜在应用。非极性面和半极性面GaN的材料外延缺少合适的衬底,自支撑衬底成本高尺寸小,异质衬底外延的晶体质量较差,难以达到较高的发光效率。于是,利用选择性横向外延技术在c面蓝宝石衬底上生长半极性面GaN材料和发光器件,可以有效降低位错密度,易于制备不同半极性面的材料和器件。本论文围绕半极性面GaN材料及器件光电性质展开研究,探索了半极性面GaN选择性横向外延的生长规律,研究了半极性面GaN的位错变化机制和光学性质；系统研究了半极性面InGaN/GaN多量子阱的光学性质,比较了半极性面和极性面InGaN/GaN多量子阱的极化特性,证明了半极性面InGaN/GaN多量子阱优异的发光特性；制备出半极性面InGaN/GaN多量子阱LED器件,探讨了器件制备过程的关键技术问题,研究了半极性面LED器件的光学性质和电学性质。研究的主要内容和获得的主要结果如下：1.分析了不同取向不同尺寸不同维度的掩膜图形上选择性横向外延生长半极性面的成面机制,证明不同晶面的形成取决于晶面表面能和表面原子的稳定性。研究发现在沿[11-20]和[1-100]方向的条形掩膜上进行选择横向外延生长,会分别形成{1-101)和{11-22}半极性面,{1-101}面的稳定性优于{11-22}面。在十字掩膜上选择横向外延生长会形成三种半极性面{1-101}、{21-33)和{11-22},其中{21-33}面会随着生长温度升高而由于热稳定性差而消失。系统研究了生长温度和掩膜填充因子等参数对半极性面微面结构形貌和不同晶面生长速度的影响。研究发现温度升高和掩膜填充因子增加都能够增加反应原子的表面迁移能力,有利于横向外延生长形成表面能较低的(0001)晶面。研究表明反应过程的生长速度是由质量输运控制。2.研究发现选择性横向外延半极性面GaN生长技术能有效减小位错密度,掩膜填充因子增大和掩膜维度增加能更有效的减小位错密度,提高晶体质量。系统分析了半极性面GaN材料的光学性质,低温PL谱观测到了分别来源于基面堆垛层错(BSF)和棱柱堆垛层错(PSF)的3.41 eV和3.29 eV附近的发光峰,证实了半极性面GaN中基面堆垛层错(BSF)主要是在横向外延区域产生。变温PL谱发现半极性面GaN材料近带边发射峰(NBE)的发光峰位随着温度的升高而红移,服从通常的能带收缩效应。而基面堆垛层错(BSF)发光峰位则随温度呈现S形非单调变化,原因是由于基面堆垛层错引起的导带和价带不连续性会导致载流子的局域化。3.对于选择性横向外延生长的半极性面InGaN/GaN多量子阱,相同生长条件下半极性面{11-22}、{1-101}和极性面(0001)的发光峰位分别为412 nm、436nm518 nm,并且同一个{1-101}晶面中顶部发光峰位相比底部发生了23nm的红移。发光峰位发生差异的主要原因是不同晶面甚至同一半极性面不同位置的生长速度不同,导致了多量子阱阱宽和In掺杂效率不同,另外选择性横向外延生长过程中的In原子迁移长度大于Ga,也会导致In的组分发生差异从而影响发光峰位。研究表明十字掩膜上生长形成的三种半极性面InGaN/GaN多量子阱的发光波长顺序为{1-101}{21-33}{11-22},与这些晶面的生长速度顺序一致。发现微面结构中c面顶面量子阱的团簇分布的不均匀发光现象,证明了相比半极性面斜面,c面顶面有着较高的位错密度而导致其InGaN生长过程中出现相分凝。4. 变功率PL研究发现半极性面多量子阱的发光峰位随激光功率增加的蓝移量仅为极性c面的1/5,证明了半极性面多量子阱极化电场大幅减小,QCSE效应大幅减弱。计算得到{1-101}和{11-22}半极性面InGaN/GaN多量子阱的内量子效率ηint分别为65.6%和55.7%,远高于c面多量子阱的内量子效率(15.9%),证实了限制极化电场导致的QCSE效应能够大幅提高InGaN/GaN多量子阱的发光性能。变温PL研究表明半极性面InGaN/GaN多量子阱的PL发光峰能量随温度升高而单调下降,不同于极性c面多量子阱中由于载流子局域化导致的“S”型关系曲线,是由于半极性面多量子阱中的弱极化电场和深阱使得载流子局域化效应减弱导致。建立了应变诱导极化模型,经过计算证明了半极性面InGaN/GaN多量子阱的压电极化强度和总极化强度比极性c面大幅减小,使得能带变平,发光峰蓝移,QCSE效应减弱,辐射复合效率提高。5.研制出了半极性面InGaN/GaN多量子阱LED器件,发现Mg掺杂能够增强Ga原子的迁移能力,促进横向生长使得半极性面pGaN层厚度远大于极性c面。研究了半极性面LED的光学性质,证明了{11-22}半极性面相比极性c面,极化电场大幅减小,QCSE效应大幅减弱。Ⅰ-Ⅴ特性结果发现制得的半极性面LED芯片的正向电压为6.3 V,反向漏电流为2 mA@-5 V,均弱于极性c面LED芯片的电性,主要是由于选择性横向外延中pGaN的外延生长工艺和非平面芯片的金属蒸镀工艺造成,表明半极性面LED的外延及芯片工艺还有待进一步优化。
[Abstract]:The band gap of III nitride materials varies from 0.7 eV to 6.2 eV, and the wavelength covers a wide spectrum range from near infrared to ultraviolet. It has excellent photoelectric properties, and has larger application range and higher luminous efficiency than other materials. These advantages make the nitride LED the most successful near ultraviolet to blue and green light. However, the nitride heterostructure is a strong polarization, high strain quantum system, and polarization discontinuity is introduced into the extremely strong internal electric field, which leads to the space separation of the electron hole wave function in the quantum well structure and the reduction of the luminescence efficiency. The research trend of the polarization is not polarized, and the research of the GaN based LED of the non polar and semi polar surfaces has been gradually paid attention to, The weakening of the polarization effect will bring more excellent photoelectric properties and huge potential applications. The material epitaxy of non polar and semi polar surface GaN is lack of suitable substrate, the cost of self supported substrate is high, the crystal quality of the heteroepitaxial substrate is poor, and it is difficult to achieve high luminous efficiency. The growth of semi polar surface GaN materials and light emitting devices on C surface sapphire substrate can effectively reduce dislocation density and be easy to prepare materials and devices with different semi polar surfaces. This paper studies the photoelectric properties of GaN materials and devices on semi polar surfaces, and explores the growth law of the semi polar surface GaN selective lateral epitaxy. The dislocation mechanism and optical properties of polar surface GaN, the optical properties of the semi polar InGaN/GaN multiple quantum well are studied systematically, and the polarization characteristics of the semi polar and polar InGaN/GaN multiple quantum well are compared. The excellent luminescence characteristics of the semi polar InGaN/GaN multiple quantum well are proved and the semi polar InGaN/GaN multi quantum well LED device is prepared. The key technical problems of the device preparation process are discussed and the optical and electrical properties of the semi polar surface LED devices are studied. The main contents and main results are as follows: 1. the surface mechanism of the selective lateral extension of the semi polar surface on the mask patterns with different dimensions and different dimensions is analyzed. The formation of the isomorphic surface depends on the surface energy and the stability of the surface atoms. It is found that the selective lateral epitaxial growth on the strip mask along the [11-20] and [1-100] directions will form {1-101) and the {11-22} semi polar surface respectively. The stability of the {1-101} surface is better than that of the {11-22} surface. The selection of lateral epitaxial growth on the cross mask will form three. A semi polar surface {1-101}, {21-33) and {11-22}, in which the {21-33} surface will disappear with the increase of the growth temperature and due to the poor thermal stability. The influence of the growth temperature and the mask filling factor on the microstructure and the growth speed of the semi polar surface micro surface and the growth rate of the different crystal surfaces is investigated. It is possible to increase the surface mobility of the reaction atoms, which is beneficial to the formation of a surface with lower surface energy (0001). The study shows that the growth rate of the reaction process is based on the mass transport control.2.. It is found that the selective lateral epitaxial semi polar surface GaN growth technique can reduce the dislocation density effectively, the mask filling factor increases and the mask can be masked. The dimension increase can reduce the dislocation density more effectively and improve the crystal quality. The optical properties of the semi polar GaN materials are systematically analyzed. The low temperature PL spectra have observed the luminescence peaks near the 3.41 eV and 3.29 eV, which are derived from the stacking fault (BSF) and the prism stacking fault (PSF) respectively, and confirmed the main surface stacking fault (BSF) in the semi polar GaN. It is produced in the lateral epitaxial region. The variation of temperature PL spectra shows that the luminescence peak of the near band edge emission peak (NBE) of the semi polar surface GaN material is redshift with the increase of temperature, and it obeys the usual band contraction effect. The luminescence peak of the base stacking stacking fault (BSF) is not monotonically changed with the temperature of S, due to the conduction band caused by the stacking fault of the base surface. The valence band discontinuities lead to the localization of the carrier.3. for the semi polar InGaN/GaN multiple quantum well with selective lateral epitaxy. The luminescence peaks of the semi polar surface {11-22}, {1-101} and polar surface (0001) under the same growth conditions are 412 nm and 436nm518 nm respectively, and the bottom of the top luminescence peak in the same {1-101} crystal surface occurs at the bottom. The main reason for the difference of the luminescence peak is that the growth rate of the different crystal surface and even the same half polar face is different, which leads to the different quantum well well width and the In doping efficiency. In addition, the In atom migration length in the selective lateral epitaxial growth is greater than that of the Ga, and the difference in the component of the In will result in the shadow of the In. The study shows that the luminescence wavelength of the three semi polar InGaN/GaN quantum well formed on the cross mask is {1-101}{21-33}{11-22}, which is in the same order as the growth rate of these crystal surfaces. It is found that the uneven luminescence of the cluster distribution of the top surface of the C surface in the surface of the micro surface proves that the half polar surface is compared with the semi polar surface. There is a high dislocation density on the top surface of the C surface, which leads to the phase segregation of.4. in the process of InGaN growth. It is found that the blue shift of the luminescence peak of the semi polar multi quantum well with the increase of laser power is only 1/5 of the polar C surface. It is proved that the polarization electric field of the semi polar multi quantum well is greatly reduced and the QCSE effect is greatly weakened. The internal quantum efficiency of the {1-101} and {11-22} semi polar InGaN/GaN quantum wells is 65.6% and 55.7% respectively, which is far higher than the internal quantum efficiency (15.9%) of the C multi quantum well. It is proved that the QCSE effect caused by the restricted polarization field can greatly improve the luminescence energy of the InGaN/GaN multi quantum well. The variable temperature PL study shows that the semi polar face is InGaN/GaN multiple. The PL luminescence peak energy of the sub well decreases monotonously with the increase of temperature. It is different from the "S" relationship curve caused by the carrier localization in the polar C multi quantum well. It is due to the weak polarization electric field and deep well in the semi polar multi quantum well which weakens the carrier localization effect. The strain induced polarization model is established. It is proved that the piezoelectric polarization intensity and the total polarization intensity of the semi polar InGaN/GaN multi quantum well are greatly reduced than the polar C surface, making the energy band leveling, the blue shift of the luminescence peak, the QCSE effect weakened, the radiation recombination efficiency improved by.5., and the semi polar InGaN/GaN multi quantum well LED device is developed. The occurrence of Mg doping can enhance the migration ability of Ga atoms and promote the migration of Ga atoms. The thickness of the semi polar surface pGaN layer is far larger than the polar C surface. The optical properties of the semi polar surface LED are studied. It is proved that the {11-22} semi polar face is compared to the polar C surface, the polarization electric field is greatly reduced and the QCSE effect is greatly weakened. The positive voltage of the semi polar plane LED core is 6.3 V and the reverse leakage current is 2 mA@-. The electrical properties of 5 V, which are all weaker than the polar C LED chips, are mainly due to the epitaxial growth process of pGaN in selective lateral epitaxy and the metal evaporation process of non planar chips, indicating that the epitaxy of the semi polar LED and the chip technology still need to be further optimized.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.2

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