【作者】 郑鹏天；

【导师】 张进成；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2009， 硕士

【摘要】 由于出色的高频大功率处理能力,AlGaN/GaN高电子迁移率晶体管(HEMT)器件成为下一代RF和微波功率放大器的理想继任者。近些年来,随着材料质量和器件工艺的不断进步,AlGaN/GaN HEMT器件的性能不断提升。与此同时,为了满足国防电子通讯应用领域和飞速发展的移动通信领域的需求,人们已经开始探求一些更高性能的器件结构,GaN基双异质结HEMT器件就是其中较为成功的一种。和传统的单异质结相比,双异质结构HEMT器件具有更强的载流子限域性,这不仅有助于提高载流子迁移率和器件的关断特性,而且有利于抑制电流崩塌效应。因此,开展GaN基双异质结HEMT器件研究是十分有意义的。本文首先从GaN基双异质结构的理论研究入手,通过一维自洽求解薛定谔／泊松方程,模拟研究了各种GaN基双异质结构中的能带结构和载流子的分布特性。模拟中主要考虑了不同背势垒层结构对载流子分布和限域性的影响。模拟结果对实验研究起到了很好的指导作用。之后,本文利用MOCVD技术生长了具有不同背势垒层结构的AlGaN/GaN双异质结材料。通过各种表征手段,对材料的结晶质量和电特性进行了对比分析。结果表明,材料具有较好的结晶质量和电学特性。采用较高Al组分的背势垒层会引起较大的界面失配,采用较厚的背势垒层会引起晶格应变驰豫,这两种情况下双异质结材料的结晶质量均受到了不利影响。从霍尔效应结果来看,由于背势垒层的引入,增加了材料的合金无序散射和界面粗糙度散射,因而双异质结构的2DEG迁移率并没有显著提高。另外,本文通过汞探针CV测试对AlGaN/GaN双异质结材料的载流子分布特性进行了研究,取得了载流子分布以及主沟道载流子限域性随背势垒层Al组分和厚度变化的规律,这些规律和本文理论计算的结果非常一致,验证了理论计算的正确性。最后,本文通过器件制造和测试,对AlGaN/GaN双异质结HEMT器件的直流输出特性、转移特性、RF小信号特性以及电流崩塌效应进行了较为深入的研究。结果表明,该器件表现非常好的直流特性和RF小信号特性。另外,受载流子浓度非常低的寄生沟道的影响,器件的跨导曲线中出现了微弱的双沟道行为；AlGaN/GaN双异质结HEMT器件中较强的载流子限域性,减弱了载流子迁移率对载流子面密度的依赖关系,因而在很宽的栅压偏置范围内,器件仍保持着较高跨导；和传统的单异质结HEMT器件相比,由于主沟道载流子限域性的增强,AlGaN/GaN双异质结HEMT器件中发生了较少的电流崩塌。更多还原

【Abstract】 Owing to their high power handling capability at high frequencies, wide bandgap AlGaN/GaN high electron mobility transistors (HEMTs) are emerging as promising candidates for next-generation RF and microwave power amplifiers. With tremendous progresses made during the last decade in material quality and device processing, AlGaN/GaN HEMTs have been improved significantly in both dc and RF performances. Meanwhile, more advanced device structures are being explored for further performance improvement. The GaN-based double-heterojunction HEMTs, for example, are one of these structures, which have been carried out successfully. Comparaed to the conventional GaN-based heterojunction, the improved carrier confinement in GaN-based double-heterojunction HEMTs may not only result in improved carrier mobility and HEMTs’pinch-off behavior, but also help to restrain the Current collapse effect. So there is great meaning to investigate the double-heterojunction HEMTs.In this paper, firstly, the theory research was carried out by the one-dimensional self-consistent simulation of the band diagram and carrier distribution of the GaN-based double heterostructures. The effect of different AlGaN back-barrier layer on the carrier distribution and confinement was mainly studied in our simulation.Secondly, the AlGaN/GaN double heterostructure materials with different back-barrier layers were designed and grown by MOCVD method on c-plane sapphire substrate. These materials show good crystal quality and high electrical characteristics. The higher interface mismatch arosed from the high Al-content in the back barrier layer, as well as the release of crystal lattice brought by the larger thickness of the back barrier layer, have bad effect on the crystal quality. Moreover, the mercury probe CV measurement was carried out to study the effect of the Al content and thickness of the AlGaN back-barrier layer on the carrier distribution and the carrier confinement. The conclusions we made from the mercury probe CV measurement are the same with the results of theoretical simulation, so the results of theoretical simulation were verified.Finally, the AlGaN/GaN double-heterojunction HEMTs were fabricated and researched to analyse the DC characterization、RF small-signal characterization and the effect of current collapse. The results we made show that our AlGaN/GaN double-heterojunction HEMT have good DC and RF characterization, and the devices are suitable for the application occasion with high power and high frequencies. Morever, a slight double channel behavior was found and explained deeply in the double-heterojunction HEMT; Attributed to the improved carrier confinement in GaN-based double-heterojunction HEMT, the dependency relationship of the carrier mobility on the carrier sheet density was weakened, which made the double-heterojunction HEMT keep higher transconductance under wide gate bias range; The improved carrier confinement also made the current collapse in the double-heterojunction HEMT is much less than that in the single-heterojunction.更多还原