基于应力调控的硅基氮化镓材料和器件研究

发布时间：2018-05-15 09:28

本文选题：Si基GaN + 应力调控　；参考：《西安电子科技大学》2015年硕士论文

【摘要】：近年来,Si基GaN材料及器件研究的关注度越来越高。Si基GaN材料具有两方面的主要优势：一方面是源于Si基衬底材料。Si衬底具有成本低、尺寸大的优点,同时自身的热导率较好,并且与传统的Si器件工艺兼容性好,基于以上的优势,Si基材料一直都被研究人员所看好。另一方面,GaN材料禁带宽,击穿电场高,热导率高以及抗辐照能力强等特点使得GaN材料成为制作高频大功率、耐高温、抗高压以及抗辐照电子器件以及光电子器件的理想材料。但是由于Si衬底与GaN外延层之间存在着较大的晶格失配和热失配,所以Si衬底上GaN外延层中受到很强的张应力,甚至材料表面容易出现裂纹,这是制约硅基GaN技术的重要难题之一。同时AlGaN/GaN异质结构和HEMT器件性能在很大程度上得益于其材料体系内部的自发极化和压电极化效应,外延薄膜中的应力会对器件性能造成显著影响。因此本文围绕应力对硅基GaN材料和器件的影响,一方面通过硅基GaN材料生长方法的研究希望能够降低GaN外延薄膜的张应力,另一方面通过施加外部应力,深入研究应力对Si基GaN HEMT器件性能的影响。本文的具体工作及结论如下：1. 针对硅基GaN外延材料应力过大和裂纹问题,通过改进应力调控过渡层的结构,有效抑制了裂纹和应力,并显著提高了硅基GaN材料的质量。首先对传统由生长程序生长的样品,进行表面形貌表征,结晶质量表征,发现材料结构中的A1N成核层以及AlGaN缓冲层对GaN外延层的影响较大。所以,本文对成核层采用在蓝宝石衬底上进行优化过的三步法生长方式进行设计,即高温A1N+低温A1N+高温A1N结构。同时为了减小生长中的品格失配问题,本文设计加入两层变铝组分的AlGaN缓冲层结构,即高铝组分的Al0.5Ga0.5N层与低铝组分的Al0.25Ga0.75N进行两步法生长。并对生长获得的Si基GaN异质结材料进行材料表征对比分析。我们发现采用新结构生长的Si基GaN材料表面没有裂纹的出现,说明由于失配导致的应力被有效的缓解释放了。同时,与样品A对比,设计生长的样品B的螺位错密度下降了一个数量级,刃位错密度下降了两个数量级。通过TEM的表征,发现位错主要湮灭在变铝组分的AlGaN缓冲层,说明渐变Al组分的AlGaN缓冲层可以有效降低Si基GaN材料内的位错。2. 研制出Si基GaN异质结材料MIS-HEMT器件样品,并对器件的直流特性和界面特性进行了深入分析研究。对MIS-HEMT器件的性能进行表征,主要对器件的欧姆接触特性、输出特性、转移特性以及栅的MIS电容特性进行表征分析。并通过C-V曲线计算获得器件的界面态密度。3. 通过应力施加台对器件施加不同程度的机械应力,并对不同应力下的器件特性进行测试。首先,通过拉曼测试发现,随着应力的增大,GaN外延层的拉曼峰位发生红移,说明GaN材料受到的张应力增大了。随后,通过对不同应力下的器件特性对比分析,发现随着外加应力的增大,器件的饱和漏电流逐渐增大,载流子的浓度也随着外加应力的增大而增大,而界面态密度却没有发生明显的变化。对比结果说明,由于界面态密度没有明显变化,所以二维电子气的增加主要是由于外加应力导致的。外加应力增大导致拉曼峰位发生红移,导致材料的载流子浓度增大,从而器件饱和输出电流增大。
[Abstract]:In recent years, more and more attention has been paid to the research of Si based GaN materials and devices..Si based GaN materials have two main advantages: one is that.Si substrate from Si based substrate has the advantages of low cost, large size, good thermal conductivity, and good compatibility with the traditional Si device technology. Based on the above advantages, Si based materials On the other hand, the GaN material has the characteristics of high high power, high thermal conductivity and strong radiation resistance, which makes GaN material become a material for making high frequency, high temperature, high temperature resistance, high pressure resistance, anti irradiation electronic devices and optoelectronic devices. But because of the memory between the Si substrate and the GaN epitaxial layer In the larger lattice mismatch and thermal mismatch, the strong Zhang Yingli in the GaN epitaxial layer on the Si substrate, and even the cracks on the surface of the material, is one of the important problems that restrict the silicon based GaN technology. At the same time, the properties of AlGaN/GaN heterostructures and HEMT devices are largely due to the spontaneous polarization and pressure within the material system. The effect of the electrical polarization, the stress in the epitaxial film will have a significant effect on the performance of the device. Therefore, in this paper, the effect of the stress on the silicon based GaN materials and devices, on the one hand, is hoped to reduce the tensile stress of the GaN epitaxial film by the study of the silicon based GaN material growth method. On the other hand, the stress on the Si based G is deeply studied by applying the external stress. The effect of aN HEMT device performance. The specific work and conclusion of this paper are as follows: 1. in view of excessive stress and crack problem of silicon based GaN epitaxial material, by improving the structure of stress regulating transition layer, the crack and stress are effectively suppressed, and the quality of silicon based GaN material is greatly improved. The surface morphology characterization, the crystallization quality characterization, the A1N nucleation layer in the material structure and the AlGaN buffer layer have great influence on the GaN epitaxial layer. Therefore, this paper designs the three step method for the optimization of the nucleation layer on the sapphire substrate, that is, the high temperature A1N+ low temperature A1N+ high temperature A1N structure. The problem of lattice mismatch is to design a AlGaN buffer layer with two layers of Al component, that is, the growth of the Al0.5Ga0.5N layer of the high aluminum component and the Al0.25Ga0.75N of the low aluminum component, and to compare the material characterization of the Si based GaN heterojunction materials obtained by the growth. We found that the surface of the Si based GaN material used for the growth of the new structure is not on the surface. The occurrence of the crack indicates that the stress caused by mismatch is released effectively. At the same time, compared with the sample A, the snail dislocation density of the designed sample B drops by one order of magnitude and the dislocation density of the blade is reduced by two orders of magnitude. By the TEM characterization, it is found that the dislocation mainly annihilated in the AlGaN buffer layer of the variable aluminum component, indicating the gradient Al group. The split AlGaN buffer layer can effectively reduce the dislocation.2. in the Si based GaN material and develop the Si based GaN heterojunction material MIS-HEMT device samples, and analyze the DC and interface characteristics of the devices. The performance of the MIS-HEMT devices is characterized, mainly the ohm contact characteristics, the output characteristics, and the transfer characteristics of the devices. The MIS capacitance characteristic of the gate is characterized and analyzed. The interface state density of the device is calculated by the C-V curve and the mechanical stress is applied to the device by the stress application to the device, and the device characteristics under different stresses are tested. First, the Raman test shows that the Raman peak of the GaN epitaxial layer occurs with the increase of the stress. The red shift indicates that the tensile stress of the GaN material is increased. Then, through the comparison and analysis of the device characteristics under different stresses, it is found that the saturation leakage current of the device increases with the increase of the applied stress, and the concentration of the carrier increases with the increase of the applied stress, but the density of the interface states has not changed obviously. It is shown that the increase of the two dimensional electron gas is mainly due to the external stress. The increase of the external stress causes the red shift of the Raman peak, which leads to the increase of the carrier concentration and the increase of the saturation output current of the device.

【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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