CAREER: Engineering Ultra-Wide Bandgap III-Nitride Devices for Highly Efficient and Robust Electronics

未来几十年，随着世界上更多的人获得电力供应，全球对能源的需求可能会大幅增加。这一需求将需要在不加剧对气候变化对环境、社会和经济影响的现有担忧的情况下得到满足，气候变化受到电力系统效率的影响。此外，由于这种效率与电力电子中使用的半导体器件相关的损耗有关，因此必须研究用一种新的半导体技术取代今天的硅基组件。宽带隙半导体是候选材料，而超宽带隙(UWBG)半导体是下一个前沿。特别是，富铝氮化镓(AlGaN)为探索新一代高效和坚固的电子设备提供了一个令人兴奋的机会。这些设备在面对高温或电磁干扰(EMI)时的健壮性也有助于提高系统性能和可靠性。到目前为止，一系列悬而未决的科学问题和技术障碍阻碍了AlGaN设备发挥其全部潜力。然而，最近氮化铝(AlN)晶片的商业化使人们首次能够研究AlGaN薄膜的理想性能。因此，这个职业项目的研究目标是了解高压AlGaN器件的操作物理，并开发工程解决方案，以释放其在电力电子中的性能，在电力电子中，效率和坚固性是关键。该研究人员还致力于通过使用基于团队、基于实验室的方法成为半导体器件领域的领先教育工作者，并热衷于确保平等接受STEM教育/培训。已确定了三项教育/外展任务，目标是：(1)通过可用于STEM职业生涯的实践研究经验，使本科生掌握适销对路的技能；(2)吸引代表性不足的少数群体，使STEM劳动力多样化；(3)提高公众对半导体/电子领域的科学素养。该职业项目的目标是了解超宽带隙AlGaN功率器件的性能限制，并建立解决方案，以在高效和坚固的系统中部署这些器件。通过实验提取自然AlN衬底上实现的雪崩光电二极管的碰撞电离系数，可以了解富Al AlGaN支持大电场的潜力。结果将被用来最小化漂移区对整体传导损耗的贡献。由于与富铝AlGaN的低阻欧姆接触仍然难以捉摸，UWBG AlGaN的表面和本体将进行设计，以获得热稳定的接触，同时降低接触电阻。利用非原位和原位中间层来补偿AlGaN的极化电荷，可以降低表面势垒高度。通过注入Si对体相AlGaN进行重掺杂，然后进行有效的激活退火热处理，也可以获得隧道接触。将探索高温运行的极限。其次，AlGaN的p型掺杂，特别是对埋藏区和横向区的掺杂，是先进功率器件的障碍。因此，将p型化合物半导体与n型AlGaN相结合的新型晶体异质集成(CHI)将被研究。将评估异质PN结的高压击穿，以及它们对光的响应，以解释所产生的能带结构并探索跨结的载流子传输。这些研究任务将被用来设计、制造和表征高压(1-5千伏)AlGaN二极管，以展示AlGaN技术在未来电力系统中的前景。还将检查它们在面对高温暴露时的稳定性。为了应对电磁干扰的风险，将研究第一个将AlGaN与其他化合物半导体异质集成的光电晶体管，以实现快速光学选通和高压阻挡。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The global demand for energy will likely significantly increase in the coming decades as more of the world gains access to electricity. This demand will need to be met without intensifying existing concerns over the environmental, societal, and economic impacts of climate change, which is influenced by the efficiency of power systems. Furthermore, since this efficiency is tied to losses associated with the semiconductor devices used in power electronics, the replacement of today’s silicon-based components with a novel semiconductor technology must be investigated. Wide bandgap semiconductors are candidates, however ultra-wide bandgap (UWBG) semiconductors represent the next frontier. In particular, aluminum-rich aluminum gallium nitride (AlGaN) offers an exciting opportunity to explore a new generation of highly efficient and robust electronic devices. The robustness of these devices in the face of elevated temperatures or electromagnetic interference (EMI) also stands to improve system performance and reliability. Thus far, a combination of unresolved scientific questions and technological barriers have prevented AlGaN devices from reaching their full potential. The recent commercialization of aluminum nitride (AlN) wafers, however, permits the ideal properties of AlGaN films to be studied for the first time. Thus, the research objective of this CAREER project is to understand the operational physics of high voltage AlGaN devices and develop engineering solutions that will unlock their performance for power electronics where efficiency and robustness are key. The investigator is also committed to becoming a leading educator in the area of semiconductor devices via the use of team-based, laboratory-based methods and is passionate about ensuring equal access to STEM education/training. Three education/outreach tasks have been defined with the objectives of: (1) equipping undergraduates with marketable skills via hands-on research experiences that they can leverage for STEM careers, (2) engaging underrepresented minority groups to diversify the STEM workforce, and (3) increasing the public’s scientific literacy surrounding semiconductors/electronics.The objective of this CAREER project is to understand the performance limits of ultra-wide bandgap AlGaN-based power devices and establish solutions to deploy these devices in highly efficient and robust systems. The potential for Al-rich AlGaN to support large electric fields will be understood by experimentally extracting the impact ionization coefficients from avalanche photodiodes realized on native AlN substrates. The results will be used to minimize the drift region’s contribution to the overall conduction loss. Since low resistance ohmic contacts to Al-rich AlGaN remain elusive, the surfaces and bulk of UWBG AlGaN will be engineered to obtain thermally stable contacts with reduced contact resistance. The surface barrier height will be reduced using both ex-situ and in-situ interlayers that compensate AlGaN’s polarization charge. Tunneling contacts will also be sought by heavily doping the bulk AlGaN via Si implantation followed by effective activation annealing. The limits of high temperature operation will be explored. Next, p-type doping of AlGaN, in particular for buried and lateral regions, is a barrier towards advanced power devices. Thus, novel Crystal Heterogeneous Integration (CHI) will be investigated to combine p-type compound semiconductors with n-type AlGaN. The high voltage breakdown of heterogeneous PN junctions will be evaluated, as well as their response to light to interpret the resulting band structures and explore carrier transport across the junction. These research tasks will be leveraged to design, fabricate, and characterize high voltage (1-5 kV) AlGaN diodes, with a view to demonstrating the promise of AlGaN technology in future power systems. Their stability in the face of high temperature exposure will also be examined. To address the risk of EMI, the first phototransistor that heterogeneously integrates AlGaN with other compound semiconductors will be investigated for fast optical gating and high voltage blocking.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.