【作者】 吕玲；

【导师】 郝跃；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2014， 博士

【摘要】 空间技术的不断发展，对电子器件的可靠性提出了更高的要求。AlGaN/GaNHEMT器件在高频、大功率、高温和高压应用方面具有超强的优势，结合GaN材料出色的抗辐照特性，该器件在卫星、太空探测、核反应堆等辐射环境中有很大的应用前景。虽然理论和已有的部分实验结果已经表明了GaN材料具有出色的抗辐照特性，但是实际情况下，由于异质外延生长的GaN材料总是存在高密度的缺陷，而且GaN HEMT器件采用了较为复杂的GaN异质结材料结构，这类异质结材料特性对表面和界面非常敏感，所有这些情况都会使得GaN基材料和HEMT器件抗辐照特性受到很大的影响和挑战。本文在此背景下，主要是从实验和理论两个方面，对GaN基半导体材料和AlGaN/GaN HEMT器件的辐照效应进行了系统的研究。通过深入分析辐照效应的退化规律，揭示了物理损伤机制，并且建立相应的数学模型，为开展器件的抗辐射加固奠定理论基础。主要研究工作和研究结果如下：1、首先，开展了AlGaN/GaN HEMT器件抗60Co γ射线辐照总剂量效应能力的实验研究，重点研究了加电条件下在线辐照模拟器件工作状态。结果表明，AlGaN/GaN HEMT器件抗γ射线辐照特性主要取决于器件的表面态对γ射线辐照的敏感程度。2、对HEMT器件的关键结构AlGaN/GaN异质结，从电学特性、晶体质量和光学特性三方面对质子辐照前后的材料进行了详细表征，为HEMT器件质子辐照效应研究提供依据。结果说明了质子辐照后异质结2DEG载流子浓度和迁移率下降，材料应力和掺杂均无变化，材料螺位错和刃位错不变。随着质子辐照注量的增加，黄带光强逐渐增强。质子辐照主要在材料中引入了Ga空位或者Ga空位相关的络合物缺陷，造成了材料光学性能的退化。3、开展了AlGaN/GaN HEMT器件的高能质子辐照效应实验研究。采用不同能量和注量的质子辐照，对器件的直流、交流特性进行详细地测试和分析。结果发现，只有高注量的质子辐照才能引起器件特性参数的退化。由于低能量质子辐照的非电离能量损失比较大，其导致器件退化更为严重。结合器件仿真软件和计算模型，讨论了AlGaN/GaN HEMT器件的质子辐照退化机制。简单的空位引入Silvaco陷阱模型中，发现只有作为受主的Ga空位对器件性能退化起作用。特性参数随质子注量的退化趋势与实验结果相一致，印证了模型的正确性。利用电荷控制模型来分析受主缺陷对2DEG面密度的影响。结果表明GaN层引入受主缺陷起主导作用，并且面密度的去除率与AlGaN势垒层非掺杂厚度、导带断续和AlGaN势垒层掺杂浓度三个参数无关。GaN层中质子辐照引入作为受主的Ga空位或者与Ga空位相关的络合物缺陷是造成AlGaN/GaN HEMT器件电学性能退化的主要原因。4、针对HEMT器件的关键结构AlGaN/GaN异质结，从电学特性、晶体质量和光学特性三方面对中子辐照前后的材料进行详细表征，为HEMT器件中子辐照效应研究提供依据。5、开展了AlGaN/GaN HEMT器件中子辐照效应的实验研究，并与同注量质子辐照进行比较。1×1015cm-2注量的中子辐照后，AlGaN/GaN HEMT器件漏极饱和电流退化明显，而阈值电压正向漂移很小，说明与载流子去除效应相比较，2DEG迁移率退化起主导作用。由于器件性能退化与NIEL成正比，同注量质子和中子辐照相比，前者导致器件电学参数退化严重。6、从表面形貌、晶体质量和发光特性三个方面，对质子和中子辐照前后的HVPE GaN材料进行详细表征。粒子辐照后黄带略微增加，而蓝带随显著降低。与同注量的质子辐照相比较，HVPE GaN材料体现出更好的抗中子辐照能力。更多还原

【Abstract】 Rapid developments of the broadband communication infrastructure haveunderscored the need for high efficiency devices that can operate reliably at highfrequencies and handle high power. Electronic devices based on the III-nitride materialssystem, like high electron mobility transistors (HEMTs), they have emerged aspromising candidates for high power applications at microwave frequencies. Moreover,GaN-based materials and devices are more radiation tolerant than GaAs and Si-basedbecause of higher displacement threshold energy. To assess the device behavior in spaceenvironment, it becomes extremely important to understand the effects of radiation andthe mechanisms underlying device degradation after exposure to radiation.In the dissertation, the radiation effects on GaN-based materials and AlGaN/GaNHEMTs are systematically studied, both experimentally and theoretically. The principalfocus of this work is on the characterization of the radiation response and degradationmechanisms, and the establishment of physical and mathematical models. The mainresults of the study are as follows:1. The total dose effects of60Co gamma radiation on static and high-frequencycharacteristics of AlGaN/GaN HEMTs are investigated experimentally in detail. Inorder to simulate the actual working status of devices in space, the devices appliedvoltages were tested on line. The results show that, the anti-irradiation property ofAlGaN/GaN HEMTs depends on the sensitivity of surface states to gamma ray.2. The effects of proton irradiation on the AlGaN/GaN heterostructures are studiedin detail, which provides a basis for the study of HEMTs. The materials before and afterproton irradiation are characterized exactly in terms of the crystal quality, electrical andoptical properties. It is observed that the concentration and mobility of2DEG decreaseafter irradiation. The Raman spectra and XRD indicate that the strain, carrierconcentration and dislocations are not affected by the proton. PL tests show that theintensity of yellow band increases with the proton fluence. Therefore, Ga vacancies orGa vacancies-related complex defects introduced by the proton radiation might causethe degradation of optical property of the AlGaN/GaN heterostructures.3. The effects of high energy proton on AlGaN/GaN HEMTs are researchedexperimentally. The DC and RF characteristics of devices were measured after theproton irradiation with the different energy and dose. It is found that only high dose ofthe proton can lead to the degradation of the parameters. Compared with the energy of 10MeV, the degradations of devices induced by3MeV proton irradiation are much moreserious, which is because the non ionizing energy loss caused by the proton with lowerenergy is much larger. Through device simulation soft and mathematical model, thedegradation mechanism of proton radiation effect is discussed in detail. Adding thesimple vacancies into Silvaco trapping model, we discover that being an acceptor-likedefect, Ga vacancies play an important part in worsening the device performances, andsimulation results match well with the trends of experimental data. The influences of theacceptor-like defects on2DEG are analyzed by introducing the charge control model. Alcomposition of the AlGaN layer, conduction band discontinuous and the dopingconcentration of AlGaN layer do not contribute to the2DEG concentration degradation.It is concluded that the Ga vacancies or Ga vacancies-related complex defectsintroduced in GaN layer maybe the primary reason for the degradation of AlGaN/GaNHEMTs performance.4. The neutron irradiation effects on the AlGaN/GaN heterostructures are studied indetail. The materials before and after neutron irradiation are characterized in terms ofthe crystal quality, electrical and optical properties.5. The neutron radiation effects on AlGaN/GaN HEMTs are studied. It is observedthat drain saturation current and transconductance decrease dramatically, and thresholdvoltage shifts slightly to the forward direction after neutron irradiation. The mobilitydegradation in the channel is mainly responsible for the decrease of deviceperformances. With the same radiation dose, the parameter degradation induced by theneutron is weaker than that by the proton.6. The HVPE GaN before and after proton and neutron irradiation arecharacterized exactly in terms of the resurface topography, crystal quality and opticalproperties. PL tests show that YL/BE increases slightly after proton irradiation, whileBL/BE decreases obviously. In comparison with the proton irradiation, HVPE GaNshows more tolerant of the neutron irradiation.更多还原