Development of Type II Superlattice IR Detectors Monolithically Integrated on Silicon Substrates.

背景由于近理想的红外传感光学特性和成熟的技术，最先进的CdHgTe（CMT）红外光电探测器目前在市场上占据主导地位。CMT探测器目前面临的主要挑战是非常高的成本和难以获得长波长所需的均匀性。此外，广泛用于生长CMT探测器的CdZnTe衬底的有限尺寸设定了CMT焦平面阵列（FPA）的像素尺寸的上限。由于外延生长技术的进步，II型超晶格（T2 SL）探测器具有比CMT探测器更低的漏电流和更高的均匀性等优点。在II型结构中，InAs和GaSb层可以以其厚度对检测波长具有相反影响的方式进行设计。因此，可以从II型超晶格（T2 SL）预期对生长不确定性的改进的容限和因此更好的均匀性。尽管历史较短，但T2 SL探测器目前正在接近最先进的CMT探测器的性能，CMT探测器已经开发了50多年。虽然T2 SL光电探测器已经显示出巨大的潜力，成为一个重要的替代CMT探测器，GaSb衬底是昂贵的或在有限的尺寸。长过剩载流子寿命和低漏电流的承诺尚未实现。更重要的是，与CMT类似，FPA的制造非常复杂，包括50多个单独的步骤，这增加了T2 SL FPA的成本。硅基T2 SL探测器的发展将极大地受益于成熟的硅基IC技术。单个Si晶片可以容纳多个大幅面FPA。读出电路和焦平面阵列在硅衬底上单片集成的可能性也大大降低了制造成本。方法分子束外延（MBE）用于在硅晶片上直接生长III-V T2 SL。分子束外延能够以每秒亚原子层的精度控制材料的沉积。该项目将开发和实施新的薄膜生长技术，用于在硅表面异质外延高质量III-V族材料。为了制造性能良好的器件，外延层中的预期位错密度大约为1.0E6/cm 2。该项目将采用标准的微加工技术，在硅片上开发高性能的光电探测器。特别地，将进行器件的表面钝化以最小化表面漏电流路径并区分穿线位错对暗电流的影响。4.目标本项目的目标是开发单片集成的基于FPA的II型硅基超晶格光电探测器。它旨在解决一些科学和技术挑战，包括最大限度地提高II型超晶格探测器的量子效率，解决硅衬底上III-V材料的生长问题，以及了解应变诱导位错对器件性能的影响。与EPSRC汇款的相关性拟议的项目与EPSRC的以下主题和研究战神密切相关：1）能源：传感器和仪器;太阳能技术;能源应用材料。2）工程：传感器和仪器;能源应用材料。3）物理科学：光子材料;能源应用材料。

BackgroundThe state-of-the-art CdHgTe (CMT) infrared photodetectors is currently dominating the market due to the near ideal optical properties for infrared sensing and well-established techniques. The current major challenges for CMT detectors are the very high cost and difficulty to obtain the required uniformity for long wavelengths. Moreover, the limited size of CdZnTe substrates widely used for growth of CMT detectors sets the upper limited of the pixel size of CMT focal plane arrays (FPA). Type II superlattice (T2SL) detectors have advantages such as lower leakage currents and greater uniformity than CMT detectors due to the advance in epitaxy growth techniques. In the type II structures, the InAs and GaSb layers can be engineered in a way that their thickness have opposite effect on the detection wavelength. Therefore, an improved tolerance to growth uncertainty and hence better uniformity can be expected from the type-II superlattice (T2SL). Despite a short history, T2SL detectors currently are approaching the performance of the state-of-the-art CMT detectors, which have been developed for over 50 years. Although T2SL photodetectors have shown great potential to be an important alternative to CMT detectors, GaSb substrates are either expensive or in limited size. The promise of long excess carrier lifetime and low leakage current is yet to be fulfilled. More importantly, similar to CMT, the FPA fabrication is very complex, consisting of over 50 individual steps, which increases the cost of T2SL FPAs. The development of T2SL detectors on Si substrates will greatly benefit from the mature Si-based IC technology. A single Si wafer can accommodate a number of large format FPAs. The possibility of monolithic integrating the read-out circuits and FPA on Si substrates also significantly reduces the fabrication cost.3. MethodologyMolecular beam epitaxy (MBE) is used to direct growth III-V T2SLs on silicon wafers. MBE is able to manipulate the deposition of materials at accuracy of sub-atomic layer per second. New thin film growth techniques will be developed and implemented in the project for hetero-epitaxy of high quality III-V materials on silicon surfaces. The expected dislocation density in the epitaxial layers is on the order of 1.0E6 per cm2 in order to fabricate well-performed devices. Standard microfabrication will be involved in this project to develop high performance photodetectors on silicon wafers. Particularly, surface passivation of the devices will be carried out to minimise the surface leakage current pathways and to distinguish the impact of threading dislocations on dark current. 4. ObjectivesThe objective of this project is to develop monolithic integration of FPAs based type II superlattice photodetectors on Si substrates. It aims to address a few scientific and technical challenges, including maximizing the quantum efficiency of type II superlattice detectors, solving growth issues of III-V materials on Si substrates, and understanding the impact of strain-induced dislocations to the device performance.5. Relevance to EPSRC's remitsThe proposed project is closely relevant to the following EPSRC's Themes and Research Ares: 1) Energy: Sensors and Instrumentation; Solar Technology; Materials for Energy Applications.2) Engineering: Sensors and Instrumentation; Materials for Energy Applications.3) Physical sciences: Photonic Materials; Materials for Energy Applications.