【作者】 曹东升；

【导师】 陆海；

【作者基本信息】 南京大学 ， 微电子与固体电子学， 2011， 硕士

【摘要】 以Si, GaAs等传统半导体材料为基础的器件由于受到材料本身属性的限制,在功率半导体器件的相应指标上很难再有进一步的提高。近年来以Ⅲ族氮化物为代表的新一代宽禁带半导体材料发展迅猛。GaN具有宽带隙、高饱和电子漂移速率、高击穿场强和高热导率等优越材料性能,在紫外到可见光电子器件以及高频、高温、大功率电子器件领域极具发展潜力。然而由于异质外延GaN外延材料的缺陷密度很高,器件性能会受到很大影响。在这篇论文里,我们对基于GaN体材料衬底的低缺陷密度同质外延肖特基二极管的电流传输机理和AlGaN/GaN基平面肖特基二极管击穿做出了研究。首先,我们研究了通过金属有机源化学汽相沉积生长在GaN衬底上的同质外延GaN肖特基二极管随温度变化的电学特性。通过阴极射线发光扫描技术,我们算出GaN外延层中的位错密度约为4×106cm-2,这一密度与X射线衍射实验得到的结果一致。这种垂直结构的二极管在室温下反向偏压20 V时的反向漏电流为10-10A量级,同时具有0.9 V的低开启电压和1.5 mΩ·cm2的低开启电阻。由于肖特基势垒的不均匀性分布,在300 K到410 K的变温测量中,我们观测到了随温度升高而升高的势垒高度和随温度升高而降低的理想常数。同时我们测量到的反向漏电流与热电子发射理论模型的值相差很大,因此我们提出了一种以材料缺陷为主要漏电通道的修正热场发射模型来拟合随温度和场强变化的反向漏电流曲线。通过拟合得到的漏电流曲线和实验曲线匹配得较好。然后,我们制备了肖特基-欧姆接触间距不同的没有终端结构的AlGaN/GaN基平面肖特基二极管器件。测量发现,随着AlGaN/GaN界面处二维电子气的完全耗尽,反向漏电流在很低的反向偏压下就很快饱和了。同时我们也发现器件的击穿电压VBR与肖特基-欧姆接触间距成正比关系,其中在间距为20μm的时候,击穿电压超过了1100V,得到了超过280 MW·cm-2的优值系数。我们采用了"natural super-junction"理论来解释这一系列实验结果。更多还原

【Abstract】 In recent years, the performance of power devices based on conventional semiconductors such as Si and GaAs is limited by their intrinsic material parameters. Wide band gap semiconductor materials, especiallyⅢ-nitrides (GaN, AlN, InN) and their compounds, have been a subject of intensive investigation during the last decades, which have exhibited promising potentials in UV-to-visible optoelectronic device applications as well as high frequency, high temperature and high power devices due to their outstanding properties such as wide bandgap energy, high electron saturation velocity, large breakdown electrical field and high thermal conductivity. However, heteroepitaxial GaN-based devices commonly suffer from high dislocation density within the GaN epi-layers, which seriously limits the device performance. In this work, we studied the leakage transport mechanism of homoepitaxial GaN Schottky barrier diodes and the breakdown mechanism of AlGaN/GaN-based planar Schottky barrier diodes.Firstly, we investigated temperature-dependent electrical characteristics of Schottky barrier diodes fabricated on homoepitaxial GaN grown by metal organic chemical vapor deposition on bulk GaN substrate. The dislocation density of the GaN homoepitaxial layer is estimated to be～4×106 cm-2 by cathodoluminescence mapping technique,which agrees with the x-ray diffraction measurements. The diode fabricated with a vertical geometry exhibits a low reverse leakage of～10-10 A at-20 V, a low turn-on voltage of～0.9 V, and a low on-resistance of～1.5 mΩ·cm2 at room temperature (RT). Within the temperature range of 300 K and 410 K, the Schottky barrier height and ideality factor are observed to increase and decrease respectively with increasing temperature due to barrier inhomogeneity. Large deviations of reverse leakage from the thermionic emission (TE) mechanism were observed. A modified thermionic-field emission (TFE) model was proposed to fit the temperature and field dependent reverse leakage in which the dislocations are believed to be the primary channels of the reverse leakage. Based on our purposed model, the simulated reverse leakage curves agree well with the experimental curves.Then, AlGaN/GaN-based planar Schottky barrier diodes with various spacings between ohmic and Schottky contacts are fabricated without any edge termination. The reverse leakage current of the devices quickly saturates at low reverse bias when the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface is fully depleted. The corresponding breakdown voltage is found to follow a linear dependence on contact spacing and exceeds 1100 V at a contact spacing of 20μm, yielding a high VBR2/RON value of>280 MW·cm-2. The observations are tentatively explained by a "natural super-junction" theory.更多还原