【作者】 王福学；

【导师】 陆海；

【作者基本信息】 南京大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 第三代半导体材料GaN,具有直接带隙、大禁带宽度(室温下3.39eV)、强击穿电场(3 MV/cm)、高电子饱和漂移速度(3×107cm/s)、和良好化学稳定性等优异特性,在短波长蓝光-紫外光发光器件、微波器件和功率电子器件领域有巨大的应用前景。许多国家都投入了大量的人力、物力和财力对此进行研究。本论文主要围绕GaN自支撑体材料衬底的缺陷和杂质分布、表面处理对GaN和AlGaN/GaN肖特基二极管的性能影响、Si衬底AlGaN/GaN大功率器件的击穿和其他特性开展研究。主要研究内容和获得的结果如下：1.利用阴极荧光(CL)技术研究了用氢化物气相外延(HVPE)方法生长的GaN体材料衬底的缺陷和杂质分布。发现：GaN体材料表面显示为黑色核心的位错团簇被像光盘一样的强发光区域区域包围；这种发光的不均匀性在同质外延GaN薄膜上消失；制备在同质外延层上的肖特基二极管的反向漏电流普遍减小；但是,位错团簇的存在限制了基于GaN体材料衬底器件的产率。2.研究了氧等离子体处理GaN表面对其肖特基二极管的影响。在淀积肖特基金属之前采用ICP氧等离子体处理了GaN材料的表面,测量发现：在小偏压下,处理过的器件的反向漏电流减小、串联电阻增加；但是,在高反向偏压下,氧等离子体处理过的GaN肖特基二极管的漏电流反而更大,且击穿电压减小。XPS谱表明在氧等离子体处理过程中,GaN表面会生成超薄GaOx薄膜。在亚带宽(sub-bandgap)光照的情况下,等离子体处理过的器件有比较大的光导响应,表明氧等离子体处理过程中GaN材料表面产生了额外的缺陷态。还研究了氧等离子体处理AlGaN/GaN异质结表面对其肖特基二极管的影响,变频C-V测量表明氧等离子体处理在AlGaN/GaN异质结表面同样产生了额外的缺陷态。此外,还研究了超薄介质夹层、CF4+O2等离子体处理、热退火处理等对AlGaN/GaN肖特基二极管性能的影响。3.在Si衬底AlGaN/GaN异质结上制备了不同欧姆和肖特基接触间距的平面肖特基二极管。研究了SiO2和SiNx/SiO2复合结构钝化对Si衬底AlGaN/GaN肖特基二极管击穿特性的影响,发现SiO2和SiNx/SiO2复合结构钝化都能有效减小肖特基器件的反向漏电流并提高击穿电压,其中SiNx/SiO2复合结构的钝化效果更为显著。SiO2钝化的AlGaN/GaN肖特基二极管的最高击穿电压达到了近600V,其功率优值系数(VBR/RON)超过112MV·cm-2。当欧姆与肖特基电极间距超过一临界值后,器件的击穿电压趋于饱和；这时,器件的击穿主要发生在Si衬底和GaN外延层的界面处。更多还原

【Abstract】 GaN, as a third-generation semiconductor material, has shown great prospect in applications of short wavelength blue and ultraviolet (UV) light-emitting devices (LEDs), microwave devices and high-power semiconductor devices, due to its unique properties such as wide direct bandgap (3.39 eV), high breakdown electrical field (3MV/cm), high electron saturation velocity (3×10’cm/s), high thermal conductivity, high thermal stability, and so on. Many countries have put a lot of manpower, material and financial resources to study it.In this dissertation, we studied defect and impurity distributions in free-standing bulk GaN substrate, the effect of surface treatment on the performance of GaN- and AlGaN/GaN-based Schottky barrier diodes, and the breakdown characteristics of AlGaN/GaN-based Schottky barrier diodes fabricated on Si substrate. The main conclusions are listed as follows:1. Cathodoluminescence (CL) spectroscopy and mapping technique were used to study defect and impurity distributions in free-standing bulk GaN substrates prepared by hydride vapor phase epitaxy. It was found that, in the bulk GaN substrates investigated, dislocation clusters appearing as dark cores in the CL map were surrounded by bright disk-like regions with higher luminescence efficiency than that of the outside areas. This large-area luminescence non-uniformity disappeared in homoepitaxial GaN grown on top of the GaN substrate. Schottky barrier diodes fabricated on the homo-epilayer exhibited low average reverse leakage current, while dislocation clusters duplicated from the original bulk GaN substrate still limited device yield.2. The effect of oxygen plasma treatment on the performance of GaN Schottky barrier diodes is studied. The GaN surface is intentionally exposed to oxygen plasma generated in an inductively coupled plasma etching system before Schottky metal deposition. The reverse leakage current of the treated diodes is suppressed in low bias range with enhanced diode ideality factor and series resistance. However, in high bias range the treated diodes exhibit higher reverse leakage current and corresponding lower breakdown voltage. The X-ray photoelectron spectroscopy analysis reveals the growth of a thin GaOx layer on GaN surface during oxygen plasma treatment. Under sub-bandgap light illumination, the plasma-treated diodes show larger photovoltaic response compared with that of untreated GaN diodes, suggesting that additional defect states at GaN surface are induced by the oxygen plasma treatment.In addition, the effect of O2 plasma treatment, ultra-thin dielectric inter-layer, CF4+O2 plasma treatment, and thermal annealing on the performance of AlGaN/GaN Schottky barrier diodes was also studied.3. AlGaN/GaN-based planar Schottky barrier diodes with various spacings between ohmic and Schottky contacts were fabricated on silicon substrate. The effect of SiO2 and SiNx/SiO2 surface passivation on the breakdown characteristics of the Schottky barrier diodes was studied. SiO2 and SiNx/SiO2 surface passivation are found both effective to suppress the reverse leakage current and increase the breakdown voltage of the diodes. The diodes with SiO2 surface passivation exhibits a maximum breakdown voltage (VBR) of-600 V at a contact spacing of 20μm, producing a high VBR2/RON value of>112 MW·cm-2. The breakdown voltage of the diodes fabricated on Si substrates tends to saturates as the contact spacing exceeds a critical value, which.is believed caused by electrical breakdown occurring at the Si/GaN interface.更多还原