GaN基HEMT器件的变温特性研究

发布时间：2018-05-12 10:06

本文选题：AlGaN/GaN + 温度特性　；参考：《西安电子科技大学》2015年硕士论文

【摘要】：由于Ga N材料具有许多杰出的特性,例如高的击穿场强、高的面电荷密度和高的电子迁移率,使得AlGaN/GaN HEMTs器件已经广泛地应用于高频和高功率领域,而温度可靠性是阻碍器件进一步发展的关键问题之一,所以为了提升器件的性能,研究器件的温度特性是十分必要的。在这样的研究背景下,本篇论文将主要围绕Ga N基器件的变温特性尤其是低温下器件的特性展开研究。论文利用Silvaco软件对器件的变温特性进行了仿真,首先介绍了Silvaco的基本模型及数值计算方法,然后对比了不同器件结构的导带图差异。接着分别研究了器件在不同温度下的电场分布和热分布特性,发现随着温度的降低,电场强度减弱。在150K~450K温度范围内对晶格温度进行了提取,发现器件的强场高温点基本上位于器件栅极靠近漏极一侧的亚微米区域,并提出了降低结温和减小自热效应的方法。接着,在低温77K~200K范围内对器件的输出和转移特性进行了仿真,发现随着温度的降低,器件的饱和输出电流增大,跨导峰值增加。从转移曲线中又进一步得到了阈值电压随温度的变化关系,由于阈值电压主要与二维电子气的密度有关,所以利用1D Possion仿真软件在50K~500K温度下对2DEG的浓度及AlGaN和Ga N的导带差进行了仿真,发现随着温度的降低导带差增大,所以低温下沟道电子数量增多。此外,还进一步分析了Al组分和势垒层厚度对2DEG浓度的影响。论文在77K~270K下对Al Ga N/GaN HEMT器件进行了低温直流特性测试,对器件的输出特性和转移特性分别进行了分析,得到的结论与仿真结果相当吻合。并用TLM测量的方法研究了温度对电子迁移率的影响,发现迁移率随温度的降低而增大,并对影响电子迁移率的不同散射机制进行了简要说明。论文还利用DLTS(深能级瞬态谱仪)对器件的变温C-V特性和陷阱特性进行了测试和分析,发现随着温度的降低器件的阈值电压正向漂移这一反常现象,认为可能是由于界面态陷阱的影响导致了C-V曲线的不稳定,我们通过Arrenius分析对陷阱进行了表征,并推测出陷阱的类型,确定了陷阱的能级位置和俘获截面。论文在400K-120K温度范围内对AlGaN/Ga N器件的正反向栅漏电特性进行了研究,用热电子发射模型提取了理想因子和肖特基势垒高度。发现当温度低于200K时,漏电流几乎不随温度变化,因此推断出FN(Fowler-Nordheim)隧穿机制是低温下漏电的主导机制。对反向漏电机制用FP(Frenkel-Poole)发射和FN隧穿模型分别进行了分析,提取出的高频介电常数4)和陷阱势垒高度与相关报道非常吻合。
[Abstract]:Due to many outstanding characteristics of gan, such as high breakdown field strength, high surface charge density and high electron mobility, AlGaN/GaN HEMTs devices have been widely used in high frequency and high power fields. The temperature reliability is one of the key problems that hinder the further development of the device, so in order to improve the performance of the device, it is very necessary to study the temperature characteristics of the device. In such a background, this thesis will focus on the characteristics of gan based devices at variable temperature, especially at low temperature. In this paper, the variable temperature characteristic of the device is simulated by Silvaco software. Firstly, the basic model and numerical calculation method of Silvaco are introduced, and then the difference of the conduction band diagram of different device structures is compared. Then the electric field distribution and thermal distribution of the device at different temperatures are studied, and it is found that the electric field intensity decreases with the decrease of temperature. The lattice temperature is extracted in the range of 150K~450K temperature. It is found that the high temperature point of the device is basically located in the sub-micron region near the drain side of the gate of the device, and a method to reduce the junction temperature and reduce the self-heating effect is proposed. Then, the output and transfer characteristics of the device are simulated in the range of low temperature 77K~200K. It is found that the saturation output current increases and the transconductance peak increases with the decrease of temperature. The relationship between threshold voltage and temperature is further obtained from the transfer curve, because the threshold voltage is mainly related to the density of two-dimensional electron gas. So the concentration of 2DEG and the conduction band difference between AlGaN and gan are simulated at 50K~500K temperature by using 1D Possion simulation software. It is found that the number of channel electrons increases with the decrease of temperature. In addition, the effects of Al composition and barrier thickness on the concentration of 2DEG were further analyzed. In this paper, the low-temperature DC characteristics of Al Ga N/GaN HEMT devices are tested under 77K~270K. The output characteristics and transfer characteristics of the devices are analyzed, and the results are in good agreement with the simulation results. The effect of temperature on electron mobility is studied by TLM measurement. It is found that the mobility increases with the decrease of temperature, and the different scattering mechanisms affecting electron mobility are briefly explained. DLTS (deep level transient spectrometer) is also used to test and analyze the variable-temperature C-V and trap characteristics of the device. It is found that with the decrease of temperature, the positive drift of the threshold voltage of the device is abnormal. It is suggested that the instability of C-V curves may be due to the influence of interfacial state traps. We characterize the traps by Arrenius analysis, infer the types of traps, and determine the energy level positions and trapping cross sections of traps. In this paper, the forward and backward gate leakage characteristics of AlGaN/Ga N devices are studied in the 400K-120K temperature range. The ideal factor and Schottky barrier height are extracted by using the hot electron emission model. It is found that the leakage current almost does not change with the temperature when the temperature is below 200K, so it is inferred that the FNN Fowler-Nordheimm) tunneling mechanism is the dominant mechanism of leakage at low temperature. The reverse leakage mechanism is analyzed by FPN Frenkel-Poole emission model and FN tunneling model respectively. The extracted high frequency dielectric constant 4) and trap barrier height are in good agreement with the related reports.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN386

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