氮化镓基高电子迁移率晶体管电学可靠性研究

发布时间：2018-04-24 09:03

本文选题：电学可靠性 + 氮化镓　；参考：《江南大学》2017年博士论文

【摘要】：由于氮化镓(GaN)材料具有大禁带宽度、强击穿电场、高电子迁移率和高饱和电子漂移速度等优越的物理特性,GaN基电子器件比硅基电子器件更适合在高温、高压与高频等极端条件下工作。尤其是基于AlGaN/GaN或晶格匹配In_0.17Al_0.83N/GaN异质结形成的GaN基高电子迁移率晶体管(HEMT),凭借其良好的高频和大功率特性,成为电力电子、无线通信和雷达等领域的核心器件。除此之外,GaN材料具有稳定的化学性能,且利用其制备的HEMT检测器件灵敏度较高,使得近年来GaN基HEMT在生物和光电检测领域的应用也越来越广泛。但是,尽管GaN基HEMT的性能正不断取得突破,该器件的大规模商业化应用仍受到各种电学可靠性问题的限制。研究此类可靠性问题的物理本质,推动GaN基HEMT在微波功率和检测领域全面发展和应用,具有非常重要的科学意义与实用价值。鉴于此,本论文较深入地研究了GaN基HEMT中一些重要的电学可靠性问题,主要包括肖特基特性、电容特性、栅漏电流传输机制以及栅漏电流退化机制等。首先,根据实验需要设计并制备了不同结构的器件样品;然后,综合运用多种光电测试技术对样品进行测试;再结合半导体理论分析测试结果,深入探究可靠性问题的物理本质;最后,建立合适的物理模型,并提出了提高器件可靠性的一些可行方法。论文的主要研究内容概述如下。1.制备了两种重要的异质结HEMT器件:AlGaN/GaN HEMT和晶格匹配In_0.17Al_0.83N/GaN HEMT;另外,为了方便研究栅极特性,制备了与HEMT结构栅特性等效的肖特基二极管结构。众多研究表明,AlGaN/GaN HEMT的制备工艺相对成熟,但是异质界面材料之间晶格不匹配导致的可靠性问题不容忽视;而实现晶格匹配的In_0.17Al_0.83N/GaN HEMT具有更好的性能,但是由于材料生长比较困难,材料中常存在多种类型的缺陷,因此也会导致一些新的可靠性问题。本文通过对这两种器件的比较分析,对多个电学可靠性问题进行了深入的研究。2.研究了GaN基HEMT的反向击穿行为和正向电流传输机制,有益于提高器件的肖特基特性。尽管In_0.17Al_0.83N/GaN肖特基二极管具有较大的肖特基势垒高度,但其反向漏电流较大且反向击穿电压较低,发生了过早击穿。使用光发射显微镜(EMMI)检测击穿后的器件发现,不同于AlGaN/GaN肖特基二极管的纵向击穿,In_0.17Al_0.83N/GaN肖特基二极管的击穿方向为横向;InAlN势垒层的高密度缺陷是引起过早击穿行为的主要原因。基于多种电流模型对GaN基HEMT的正向电流进行拟合,发现传统的热发射电流只在体电阻效应显著的高偏压下占主导,低偏电流主要为缺陷辅助隧穿电流。为了全面提高GaN基HEMT肖特基性能,采用合适的钝化技术并提高势垒层质量很有必要。3.表征了GaN基HEMT的异质界面缺陷,并解释了积累区电容随频率增加的反常现象,有利于提高器件高频应用的可靠性。采用电容-电压(C-V)平行电导法分析耗尽区电容频率散射曲线发现,AlGaN/GaN HEMT异质界面存在高密度的浅能级界面缺陷,缺陷能级主要集中在0.13eV-0.16eV,而实现晶格匹配的In_0.17Al_0.83N/GaN HEMT异质界面基本不存在界面缺陷。通过测试GaN基HEMT的积累区C-V变频曲线,发现高频下电容随频率的增加而增加,传统模型无法解释该现象。通过考虑漏电流、串联电阻和界面缺陷等非理想因素,对传统模型进行了修正;修正后的模型拟合结果能与实验结果很好地吻合,证明该现象是漏电流与界面态俘获电子共同作用的结果。4.澄清了GaN基HEMT反向栅漏电流的传输机制,为进一步降低栅漏电流提供了理论指导。在考虑极化电场的影响下,通过验证变温电流-电压(I-V)曲线,发现AlGaN/GaN HEMT的反向电流主要由Frenkel-Poole(FP)发射机制主导,偏压继续增加,电流逐渐趋于饱和;晶格匹配In_0.17Al_0.83N/GaN HEMT反向低偏电流也为FP发射电流,但随偏压增加,较强的极化电场通过弯曲能带形成三角势垒,发生Fowler-Nordheim(FN)隧穿。此外,解释了零偏压下的电流平衡问题:通过比较极小偏压下的电流温度依赖关系,发现零偏下的反向电流是被正向隧穿电流抵消的。5.提出了一个由高场FN隧穿导致GaN基HEMT栅漏电流退化的模型。在无应力晶格匹配In_0.17Al_0.83N/GaN HEMT中观察到栅漏电流的典型退化行为,表明经典的逆压电模型并不是导致GaN基HEMT退化的主要机制。由此提出一个新的模型,强调高场FN隧穿过程释放的能量通过热效应产生新的缺陷,成为导致栅漏电流退化的主要原因;而退化产生的新缺陷主要在GaN层,可能为N空位。此外,还研究了源-漏应力导致的晶格匹配In_0.17Al_0.83N/GaN HEMT栅漏电流退化现象,由于该退化受温度和栅压影响明显,所以沟道热电子被认为是产生退化的主要原因。
[Abstract]:The GaN based electronic devices are more suitable for working in extreme conditions such as high temperature, high pressure and high frequency, especially based on AlGaN/GaN or lattice matching In_0.17Al_0.83N/GaN heterogeneity, because of the advantages of large gap width, strong electric field, high electron mobility and high saturation electron drift speed, and so on. The GaN materials are more suitable for high temperature, high pressure and high frequency than the silicon based electronic devices. GaN based high electron mobility transistor (HEMT) has become the core component in the fields of power electronics, wireless communication and radar, with its good high frequency and high power characteristics. In addition, the GaN material has stable chemical properties, and the sensitivity of the HEMT detection device is high, which makes the GaN based HEMT in biology in recent years. The application of the photoelectric detection field is becoming more and more widespread. However, although the performance of the GaN based HEMT is constantly breaking through, the large-scale commercialized application of the device is still restricted by various electrical reliability problems. The physical essence of this kind of reliability problem is studied, and the GaN based HEMT has been developed and applied in the field of microwave power and detection. It has very important scientific and practical value. In view of this, this paper has studied some important electrical reliability problems in GaN based HEMT, mainly including Schottky characteristics, capacitance characteristics, gate leakage current transmission mechanism and gate leakage current degradation mechanism. First, according to the experiment, different structures are designed and prepared. Then, a variety of photoelectric testing techniques are used to test the samples, and then the physical nature of the reliability problem is explored in depth with the analysis of the results of semiconductor theory. Finally, a suitable physical model is established and some feasible methods to improve the reliability of the device are proposed. The main contents of this paper are summarized as follows:.1. preparation Two important heterojunction HEMT devices: AlGaN/GaN HEMT and lattice matching In_0.17Al_0.83N/GaN HEMT; in addition, in order to facilitate the study of grid properties, the Schottky diode structure equivalent to the HEMT structural grid properties is prepared. Many studies have shown that the preparation process of AlGaN/GaN HEMT is mature, but the lattice mismatch between the heterogeneous interface materials is not matched. The problem of reliability can not be ignored, and the In_0.17Al_0.83N/GaN HEMT for lattice matching has better performance. However, because of the difficult material growth, there are many kinds of defects in the material, so it will also lead to some new reliability problems. In this paper, by comparing and analyzing these two devices, this paper is reliable to multiple electrical reliability. An in-depth study of the sexual problem has been carried out by.2.. The reverse breakdown behavior and forward current transmission mechanism of the GaN based HEMT are studied. It is beneficial to improve the Schottky characteristics of the device. Although the In_0.17Al_0.83N/GaN Schottky diode has a larger Schottky barrier height, the reverse leakage current is larger and the reverse breakdown voltage is low. Through the optical emission microscope (EMMI) detection and breakdown device, it is found that the breakdown direction of the In_0.17Al_0.83N/GaN Schottky diode is transversely different from the longitudinal breakdown of the AlGaN/GaN Schottky diode; the high density defect in the InAlN barrier layer is the main cause for premature breakdown. Based on a variety of current models, the GaN based HEMT is positive. To fit the current, it is found that the traditional heat emission current is dominated by the high bias voltage of the body resistance effect, and the low bias current is mainly a defect auxiliary tunneling current. In order to improve the performance of the GaN based HEMT Schottky, the appropriate passivation technique and the improvement of the barrier layer quality are necessary to characterize the heterogeneous interface deficiency of the GaN based HEMT. It is beneficial to improve the reliability of the high frequency application of the device. The capacitance voltage (C-V) parallel conductance method is used to analyze the capacitance frequency scattering curve of the depleted region. It is found that there is a high density shallow level interface defect in the AlGaN/GaN HEMT heterointerface, and the defect level is mainly concentrated in the 0.13eV-0.16eV The In_0.17Al_0.83N/GaN HEMT heterogeneous interface with lattice matching basically does not exist interface defects. By testing the C-V frequency conversion curve of the accumulation region of GaN based HEMT, it is found that the high frequency capacitance increases with the increase of frequency. The traditional model can not explain this phenomenon. By considering the non ideal factors such as leakage current, serial resistance and interface defect, the traditional model is not ideal. The model is modified, and the corrected model fitting results can be in good agreement with the experimental results. It is proved that the phenomenon is the result of the joint effect of the leakage current and the interface state capture electron..4. clarifies the transmission mechanism of the reverse gate leakage current of the GaN based HEMT, and provides the theoretical guidance for further reducing the gate leakage current. By verifying the temperature variation current voltage (I-V) curve, it is found that the reverse current of AlGaN/GaN HEMT is dominated mainly by the Frenkel-Poole (FP) emission mechanism, the bias voltage continues to increase, the current tends to be saturated, and the lattice matching In_0.17Al_0.83N/GaN HEMT reverse low bias current also emits the current for FP, but with the increase of bias voltage, the stronger polarization electric field passes the bending energy. In addition, the current balance problem under zero bias is explained by forming a triangle barrier and Fowler-Nordheim (FN) tunneling. By comparing the current temperature dependence under the minimum bias voltage, it is found that the reverse current under the zero bias is a positive tunneling current which is offset by the forward tunneling current and presents a model that causes the GaN based HEMT gate leakage current to be degenerated by the high field FN tunneling. The typical degenerate behavior of the gate leakage current in the non stress lattice matching In_0.17Al_0.83N/GaN HEMT shows that the classical reverse piezoelectric model is not the main mechanism leading to the degradation of the GaN based HEMT. A new model is proposed, which emphasizes that the energy overheating effect released by the high field FN tunneling process produces new defects and leads to the gate leakage. The main reason for the degradation of current is that the new defects produced by the degradation are mainly in the GaN layer, which may be N vacancies. In addition, the lattice matching In_0.17Al_0.83N/GaN HEMT gate leakage current degradation caused by the source leakage stress is also studied, because the degradation is affected by the temperature and gate pressure, so the channel thermal electrons are considered to be the main cause of degradation.

【学位授予单位】：江南大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TN386

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