Ultrawide bandgap AlGaN ionizing radiation detectors

辐射探测器对于机场和许多其他安全关键地点的环境控制和危险放射性材料的监测至关重要。先进的核探测对于国家安全、核电站和军事安全来说是一个及时的问题。该项目旨在开发使用氮化铝镓晶体薄膜的高灵敏度、紧凑型核探测器，该晶体薄膜采用与蓝绿白色发光二极管相同的技术生产，并获得了2014年诺贝尔奖。 最近，使用氮化铝镓材料的这种技术的创新扩展导致了用于空气和水净化的紫外线LED以及用于电动汽车和先进军用雷达的电力电子产品。 这些发展提供了低成本和高灵敏度的性能，具有集成功能的潜力，如照明，紫外线检测，以及在单个微芯片上的无线电传输。该项目提出了材料和器件创新，探索使用氮化铝镓技术制造低成本、紧凑型和高灵敏度的核辐射探测器。 挑战在于生产高质量的材料，这些材料可以承受高温和恶劣的环境，例如在核电站中。该团队建议生产这些材料和工作电气设备，以与现有的成本更高、体积更大的传统技术进行比较。拟议的工作将导致至少2名博士生，1名非洲裔美国人和1名退伍军人目前在该小组的教育，谁将进入政府研究或先进制造业的工作。 拟议中的研究将进一步巩固南卡罗来纳州大学？公司在恶劣环境电子产品的氮化铝镓材料方面有着卓越的业绩记录。在PI的摩根州立大学，在巴尔的摩，马里兰州的一个历史上的黑人大学的休假期间，在这项工作中产生的设备将被集成到高级设计项目。该团队建议开发一个低噪声，高速，电离辐射探测器使用超宽带隙氮化铝镓外延层氮化铝/蓝宝石模板。这种三元材料抗辐射，即使在恶劣的环境中也能使器件具有非常低的漏电流。它允许与读出和功率调节电子器件以及紫外光源等其他功能进行单片集成。建议的探测器，一个2-5？采用金属有机化学气相沉积法生长出具有高内电流增益和低暗电流的μ m厚沟道场效应光电晶体管。 这将是理想的检测辐射脉冲在盖革模式，并最终更高的穿透辐射使用较厚的吸收层。该计划利用浅穿透深紫外光来改善材料开发，以获得更厚的镍-63软β辐射层。使用单色光的能力使得能够对带隙进行光谱选择性表征，这在宽带β照明下是不可能的。该团队的初步实验显示，噪声等效功率为5 fW，尽管这些晶体管的响应时间很慢，约为20秒。通过噪声研究，这是由于在氮化铝模板/沟道生长界面的电荷捕获。高电流增益部分是捕获诱导的光电导性的结果。生长解决方案包括利用厚应变工程层和/或渐变背势垒层将该界面与晶体管沟道电隔离。因此，任何加速器件的晶体生长策略或器件架构都将降低光电流，但由慢陷阱引起的洛伦兹噪声也将减少。因此，电流增益和速度之间的权衡，特有的所有探测器，是复杂的噪声的考虑，导致中心问题：有多远可以NEP和响应时间同时减少消除陷阱的影响初步分析表明，纳秒到微秒的响应时间是可能的，与复合时间在直接间隙半导体。厚沟道晶体管层的工程设计能力也直接转化为电力电子技术，因为它能够阻挡高电压。该奖项反映了NSF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。

Radiation detectors are critically important for environmental controls and monitoring of hazardous radioactive materials at airports and many others safety critical locations. Advanced nuclear detection is a timely issue for national security, nuclear power plants, and for military security. This project aims to develop highly sensitive, compact nuclear detectors using aluminum gallium nitride crystalline films produced using the same technology which was used for blue-green-white light emitting diodes and it was awarded the 2014 Nobel Prize. More recently an innovative extension of this technology using Aluminum Gallium Nitride materials has led to ultraviolet LEDs for air and water purification and power electronics for electric vehicles and advanced military radars. These developments offer low-cost and high sensitivity performance, with the potential of integrating functionalities such as lighting, ultraviolet detection, as well as radio transmission on a single microchip. This project proposes material and device innovations, to explore the use of Aluminum Gallium Nitride technology for low-cost, compact and highly sensitive nuclear radiation detectors. The challenge is the production of high quality material, which can withstand high temperatures and harsh environments, such as in a nuclear power plant. The team proposes to produce these materials and working electrical devices to benchmark against existing higher cost, bulkier legacy technology. The proposed work will lead to the education of at least 2 PhD students, 1 African American and 1 military veteran currently in the team's group, who will go into jobs in either government research or advanced manufacturing. The proposed research will further cement University of South Carolina?s track record of excellence in Aluminum Gallium Nitride materials for harsh environment electronics. During the PI's sabbatical at Morgan State University, a historically black university in Baltimore, MD, the devices produced in this work will be integrated into senior design projects.The team proposes to develop a low-noise, high speed, ionizing radiation detector using ultra-wide bandgap aluminum gallium nitride epitaxial layers on aluminum nitride/sapphire templates. This ternary material is radiation hard and leads to devices with very low leakage currents even in harsh environments. It allows for monolithic integration with readout and power conditioning electronics, as well as other functionalities such as ultraviolet light sources. The proposed detector, a 2-5?m thick channel field effect phototransistor with a high internal current gain and low dark current will be grown by metalorganic chemical vapor deposition. It will be ideal for detecting pulses of radiation in Geiger mode, and eventually higher penetration radiation using thicker absorbing layers. The program exploits the shallow penetration deep ultraviolet light to improve materials development for thicker layers for soft beta radiation from Nickel-63. The ability to use monochromatic light enables characterization with spectral selectivity to the bandgaps, not possible with broadband beta-illumination. The team's initial experiments showed noise equivalent power 5fW, although these transistors had slow response times ~20s. Through a noise study, this was attributed to charge trapping at the aluminum nitride template/channel growth interface. The high current gain was partially a consequence of trapping induced photoconductivity. The growth solutions consist of electrically isolating this interface from the transistor channel, either with a thick strain engineered layer and/or a graded back barrier layer. Thus, any crystal growth strategy or device architecture that speeds up the device will lower photocurrent, but the Lorentzian noise arising from slow traps will also be reduced. Thus the tradeoff between current gain and speed, endemic to all detectors, is complicated by noise considerations, leading to the central question: How far can NEP and response time be decreased simultaneously by eliminating the influence of traps Initial analyses indicate that Nano-second to micro-second response times are possible, consistent with recombination times in direct gap semiconductors. The capability of engineering thick channel transistor layers directly translates to power electronics as well, as it enables the ability to block high voltages.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.