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

随着世界上越来越多的人用上电，未来几十年全球对能源的需求可能会显著增加。这一需求需要在不加剧现有的对气候变化对环境、社会和经济影响的担忧的情况下得到满足，气候变化受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目前的硅基组件。宽带隙半导体是候选的，然而超宽带隙（UWBG）半导体代表了下一个前沿。特别是，富铝氮化铝镓（AlGaN）为探索新一代高效、坚固的电子设备提供了令人兴奋的机会。这些设备在高温或电磁干扰（EMI）下的坚固性也有助于提高系统性能和可靠性。到目前为止，尚未解决的科学问题和技术障碍的结合阻碍了AlGaN设备充分发挥其潜力。然而，最近氮化铝（AlN）晶圆的商业化，使AlGaN薄膜的理想性能得以首次研究。因此，本CAREER项目的研究目标是了解高压AlGaN器件的运行物理特性，并开发工程解决方案，以解锁其在电力电子领域的性能，其中效率和稳健性是关键。研究者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STEM教育/培训的平等机会。已经确定了三项教育/推广任务，其目标是：(1)通过实践研究经验为本科生提供市场技能，他们可以利用STEM职业；(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/电子产品的科学素养。CAREER项目的目标是了解基于algan的超宽带带隙功率器件的性能限制，并建立解决方案，将这些器件部署在高效可靠的系统中。富al AlGaN支持大电场的潜力将通过实验提取雪崩光电二极管在天然AlN衬底上实现的冲击电离系数来理解。结果将用于最小化漂移区域对整体传导损失的贡献。由于富铝AlGaN的低电阻欧姆接触仍然难以捉摸，因此UWBG AlGaN的表面和大部分将被设计为获得热稳定的接触，并降低接触电阻。利用原位和非原位中间层来补偿AlGaN的极化电荷，可以降低表面势垒高度。通过Si注入大量掺杂块状AlGaN，然后进行有效的活化退火，也将寻求隧道接触。将探讨高温操作的极限。其次，p型掺杂AlGaN，特别是埋区和侧区掺杂，是实现先进功率器件的障碍。因此，将p型化合物半导体与n型AlGaN结合的新型晶体非均相集成（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载流子在结上的输运。这些研究任务将用于设计、制造和表征高压（1-5千伏）AlGaN二极管，以期在未来的电力系统中展示AlGaN技术的前景。它们在高温下的稳定性也将被检验。为了解决电磁干扰的风险，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，用于快速光门控和高压阻断。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.