GaN基异质结构及HEMT器件制备研究

发布时间：2018-06-14 11:23

本文选题：氮化镓 + 异质结　；参考：《西安邮电大学》2017年硕士论文

【摘要】：因为氮化镓(GaN)基材料禁带宽度大、电子饱和漂移速度高、耐高压、抗辐照、容易形成异质结构、具有大的自发和压电极化产生的高二维电子气(2DEG)浓度,故特别适合制备新一代高频大功率电子器件和高速低耗损电力电子器件,在军用和民用领域具有极为广阔的应用前景,是当今世界上半导体领域的研究热点。本论文重点围绕GaN基异质结构和高电子迁移率晶体管(HEMT)器件存在的部分问题,开展了 N面极性GaN/AlxGa1-xN/GaN异质结构的理论研究,铁(Fe)掺杂高阻GaN材料和GaN基HEMT结构材料的金属有机物化学气相沉积(MOCVD)生长研究,以及GaN基HEMT器件的制备及电流崩塌研究。所取得的主要研究结果如下:1.首次系统研究了 N面极性GaN/AllxGa1-xN/GaN异质结构中2DEG和二维空穴气(2DHG)浓度随结构参数的变化规律,为新型N面极性GaN/AlxGa1-xN/GaN HEMT器件的设计和分析提供了有重要参考价值的理论指导。通过薛定谔方程和泊松方程的自洽求解,系统研究了 N面极性GaN/AlxGa1-xN/GaN异质结构中2DEG和2DHG浓度随GaN帽层厚度、AlGaN背势垒层厚度和铝(Al)组分x、AlGaN背势垒层和下GaN层中n型掺杂浓度的变化规律。对于非故意掺杂的N面极性GaN/AllxGai-xN/GaN异质结构,研究发现:随GaN帽层厚度的增加,上界面处的2DEG浓度从无到有,逐渐增加;下界面处的2DHG浓度略微下降,直到趋于饱和。随着AlxGa1-xN背势垒层厚度的增加,上界面处的2DEG和下界面处的2DHG浓度均增加。随着AlxGai-xN背势垒层中Al组分x的增加,上界面处的2DEG和下界面处的2DHG浓度均增加。对于AlxGa1-xN背势垒层和下GaN层中故意掺入n型杂质的N面极性GaN/AlxGa1-xN/GaN异质结构,研究发现:对AlxGa1-xN背势垒层进行n型掺杂,可形成只在上界面处存在2DEG,在下界面处不存在2DHG的异质结构,而且,上界面处的2DEG浓度随AlxGai-xN背势垒层中n型掺杂浓度的增加而增加。对下GaN层进行n型δ掺杂,随着掺杂浓度的增加,下界面处的2DHG浓度会逐渐减少直至消失;存在一个上界面处既没有2DEG、下界面处也没有2DHG的掺杂浓度范围;进一步增加下GaN层n型δ掺杂的浓度,上界面处的2DEG浓度会随着δ掺杂浓度的增加而迅速增加。揭示了 N面极性GaN/AlxGa1-xN/GaN异质结构中上界面处2DEG的四种可能起源。2.研究了铁(Fe)调制掺杂和非故意掺杂GaN高阻缓冲层对HEMT器件性能的影响,发现Fe调制掺杂高阻GaN缓冲层HEMT器件具有更好的可靠性。利用MOCVD技术,生长了具有不同Fe掺杂浓度的GaN缓冲层,研究了 Fe掺杂浓度对GaN缓冲层电阻率、表面形貌和晶体质量的影响。分别通过Fe调制掺杂和非故意掺杂方式,在4英寸蓝宝石衬底上研制出了表面形貌好、电阻率高达107Ω·cm的高阻GaN缓冲层外延材料,并以此为基础研制了 GaN/AlxGa1xN/AlN/GaN HEMT结构材料。Fe调制掺杂高阻GaN缓冲层HEMT结构材料(样品A)的平均方块电阻为348 Ω/sq,2DEG迁移率为2503 cm2/V·s;非故意掺杂高阻GaN缓冲层HEMT结构材料(样品B)的平均方块电阻为373 Ω/sq,2DEG迁移率为1926 cm2/V·s。用样品A和样品B分别研制出了 HEMT器件,其栅长3 μm、栅宽100μm、栅源间距5 μm、栅漏间距20 μm。在脉冲模式下,测量了栅极电压为2 V时,器件的转移特性和栅极漏电流特性,结果表明,Fe调制掺杂高阻GaN缓冲层HEMT具有更高的最大饱和电流密度(395 mA/mm)和更小的栅极漏电流(3.32×10-7A)。另外,在不同栅极电压应力和漏极电压应力作用下,测量了器件的直流输出特性以及转移特性,结果表明,Fe调制掺杂高阻GaN缓冲层HEMT在栅压关断应力下具有更好的可靠性。3.首次提出了源栅双场板GaN/In0.17Al0.83N/AlN/GaNHEMT器件结构。研究了不同偏压应力对无场板、栅场板和源栅双场板GaN/In0.17Al0.83N/AlN/GaNHEMT器件漏极输出电流的影响。结果表明源栅双场板HEMT器件可有效抑制与偏压应力相关的电流崩塌现象。利用MOCVD技术,在2英寸蓝宝石衬底上研制了 GaN/In0.17Al0.83N/AlN/GaN HEMT结构材料,其室温2DEG浓度和迁移率分别为2.432×1013 cm-2和850 cm2/V·s,方块电阻为302 Ω/sq。为了研究不同场板结构对器件漏极电流退化的影响,用上述材料分别研制了无场板(器件A)、只有栅场板(器件B)和具有源栅双场板(器件C)的HEMT器件,并对器件在施加偏压应力前、施加关态和开态应力后的直流特性进行了测试。发现源栅双场板结构可有效降低GaN/In0.17Al0.83N/AlN/GaN HEMT器件的漏极电流退化。在关态应力条件下,测量了上述三种器件在栅压为2 V时的直流输出特性曲线,结果表明源栅双场板器件的漏极电流降低率为3.32%,小于栅场板器件的7.57%和无场板器件的14.63%。三种器件在漏源电压为10 V时的转移特性曲线测试结果表明,在关态应力下,器件A的阈值电压向正电压方向移动,器件B和C的阈值电压无明显变化;在开态应力条件下,器件A的饱和漏极电流和峰值跨导的减小最为明显,器件B次之,器件C最小。实验结果表明,源栅双场板对抑制器件的电流崩塌效应最为有效。
[Abstract]:Since gallium nitride (GaN) based materials have large band gap, high electron saturation drift speed, high pressure resistance and radiation resistance, it is easy to form heterostructures, with high two-dimensional electron gas (2DEG) concentration produced by large spontaneous and piezoelectric polarization, so it is especially suitable for the preparation of new generation high frequency power devices and high speed and low consumption power electronic devices. The civil field has a very wide application prospect. It is a hot topic in the field of semiconductors in the world. This paper focuses on the problems of GaN based heterostructures and high electron mobility transistor (HEMT) devices, and has carried out a theoretical study of N surface polarity GaN/AlxGa1-xN/GaN heterostructures. Iron (Fe) doped high resistance GaN materials and GaN The study on the growth of metal organic chemical vapor deposition (MOCVD), the preparation of GaN based HEMT devices and the current collapse study of GaN based HEMT devices. The main results obtained are as follows: 1. the changes of the concentration of 2DEG and two-dimensional air (2DHG) in the N surface polar GaN/AllxGa1-xN/GaN heterostructure with the structural parameters were studied for the first time. The theoretical guidance for the design and analysis of a new N surface polar GaN/AlxGa1-xN/GaN HEMT device is provided. Through the self consistent solution of the Schrodinger equation and Poisson equation, the 2DEG and 2DHG concentrations in N surface polar GaN/AlxGa1-xN/GaN heterostructures are studied with GaN cap thickness, AlGaN back barrier thickness and X of Al (Al) components. The variation of N type doping concentration in the lGaN back barrier layer and the lower GaN layer. For the unintentionally doped N surface polar GaN/AllxGai-xN/GaN heterostructure, it is found that the concentration of 2DEG at the upper interface increases gradually with the increase of the thickness of the GaN cap, and the concentration of 2DHG at the lower interface decreases slightly until it tends to saturation. With the AlxGa1-xN back potential With the increase of the thickness of the barrier layer, the concentration of 2DHG at the 2DEG and the lower interface at the upper interface increases. With the increase of Al component X in the AlxGai-xN back barrier layer, the 2DEG and the 2DHG concentration at the lower interface are all increased. For the AlxGa1-xN back barrier layer and the lower GaN layer, the N surface polar GaN/AlxGa1-xN/GaN heterostructure, which is deliberately doped with N type impurities, is studied. It is found that N type doping on the AlxGa1-xN back barrier layer can form 2DEG only at the upper interface, and there is no 2DHG heterostructure at the lower interface. Moreover, the 2DEG concentration at the upper interface increases with the increase of N type doping concentration in the AlxGai-xN back barrier layer. The N type delta doping on the lower GaN layer is 2, with the increase of doping concentration, 2 at the lower interface. The concentration of DHG will gradually decrease and disappear; there is no 2DEG and no 2DHG doping concentration at the upper interface, and the concentration of N delta doping at the lower GaN layer is further increased. The concentration of 2DEG at the upper interface will increase rapidly with the increase of the delta doping concentration. The upper boundary of the N surface polar GaN/AlxGa1-xN/GaN heterostructure is revealed. Four possible origins of 2DEG at the surface.2. studied the effect of iron (Fe) modulation doping and unintentionally doped GaN high resistance buffer layer on the performance of HEMT devices. It was found that Fe modulation doped high resistance GaN buffer layer HEMT device had better reliability. The GaN buffer layer with different Fe doping concentration was grown by MOCVD technology. The influence of the resistivity, surface morphology and crystal quality of the buffer layer. By Fe modulation doping and unintentional doping, a high resistance GaN buffer layer epitaxial material with good surface morphology and a resistivity of 107 Omega cm was developed on the 4 inch sapphire substrate. On this basis, the.Fe modulation mixing of the GaN/AlxGa1xN/AlN/GaN HEMT structure material was developed. The average block resistance of the hybrid high resistance GaN buffer layer HEMT structure material (sample A) is 348 Omega /sq and the 2DEG mobility is 2503 cm2/V. S; the average block resistance of the unintentionally doped high resistance GaN buffer layer HEMT structure material (sample B) is 373 Omega /sq, the 2DEG mobility is 1926. The gate width is 100 mu m, the distance between the gate source is 5 mu and the gate leakage distance is 20 mu m.. Under the pulse mode, the transfer characteristics and gate leakage current characteristics of the device are measured when the gate voltage is 2 V. The results show that the Fe modulation doped high resistance GaN buffer layer HEMT has a higher maximum saturation current density (395 mA/ mm) and a smaller gate leakage current (3.32 x 10-7A). Under the action of the grid voltage stress and the leakage voltage stress, the DC output characteristics and the transfer characteristics of the device are measured. The results show that the Fe modulation doped high resistance GaN buffer layer HEMT has better reliability under the gate pressure off stress..3. first proposed the structure of the source gate double field plate GaN/ In0.17Al0.83N/AlN/GaNHEMT device. The effect of compressive stress on the leakage current of the field plate, gate field plate and source gate double field plate GaN/In0.17Al0.83N/AlN/GaNHEMT device. The results show that the source grid dual field plate HEMT device can effectively suppress the current collapse associated with the bias stress. The GaN/In0.17Al0.83N/AlN/GaN HEMT structure has been developed on 2 inch sapphire substrate by MOCVD technology. The 2DEG concentration and mobility of the material at room temperature are 2.432 x 1013 cm-2 and 850 cm2/V. S respectively, and the block resistance is 302 Omega /sq.. In order to study the effect of different field plate structures on the depolarization of the leakage current of the device, the field plate (device A) is developed with the above materials, only the gate field plate (device B) and the HEMT device with the source gate double field plate (device C) are used. The DC characteristics of the device are tested before applying the bias stress and the closed state and open state stresses are tested. It is found that the source gate double field plate structure can effectively reduce the depolarization of the leakage current of GaN/In0.17Al0.83N/AlN/GaN HEMT device. The output characteristic curve of the three devices under the gate pressure of 2 V is measured under the closed state stress. The leakage current reduction rate of the gate dual field plate device is 3.32%. The test results of the transfer characteristic curves of three kinds of 14.63%. devices less than the gate field plate devices and the 7.57% field free plate devices at the leakage source voltage of 10 V show that the threshold voltage of the device A moves towards the positive voltage side under the closed state stress, and the threshold voltage of the device B and C has no obvious change. Under the open state stress condition, the saturation leakage current and the peak transconductance of the device A are the most obvious, the device is B and the device C is the smallest. The experimental results show that the source grid double field plate is most effective for the current collapse effect of the suppression device.
【学位授予单位】：西安邮电大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN386

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