Infrared and Device Physics of Quantum Well Structures

9809746Perera拟议的项目涉及研究新的多量子阱（MQW）的概念，带内过程和红外探测器操作导致焦平面质量的显着改善，并在高性能红外成像系统的潜在应用。 在以前的NSF计划中，重点放在远红外（FIR）检测的光电发射同质结检测器格式上。 这些研究导致了新的FIR探测器系列的成功开发，具有创纪录的波长截止值。 对于在较短波长（长波红外-甚长波红外）的最佳操作，量子阱红外光电探测器（量子阱的），它可以是带隙工程更有选择性的光谱响应，prefered.Recent分析总结在这个建议已经表明，当在稳态光电导模式下操作时，红外量子阱探测器经历了一个初始的瞬态过程中，广泛的重新分配和耗尽的载流子在井中可能会发生。 贡献信号电流的威尔斯阱的数量迅速减少，并且响应度和探测率显著下降，使得不能实现这种探测器的全部潜力。 在与其他大学（康奈尔大学，NRC和加州大学洛杉矶分校）和国家实验室（喷气推进实验室和美国陆军研究实验室）的科学家合作下，这个问题将通过探索探测器在瞬态而不是稳态模式下的操作来解决。 我们的初步目标是实验研究和模拟原型LWIR-VLWIR量子阱探测器的瞬态IR行为，并建立稳态模式下IR响应的时间相关操作物理。 带内能级，以及掺杂，势垒参数，发射极/集电极结构等的影响的IR响应和暗电流的瞬态值的作用将被调查。 将设计用于重新填充威尔斯和周期性提取信号电流的时变操作偏置条件。 扩展到最近的瞬态模式的检测和多层GaAs/AlGaAs结构中的空间电荷分布的分析，传感器响应的频率和偏置依赖性的研究将继续进行，目的是建立最佳的操作参数。 优化设计的功能，良好的掺杂配置文件，能量选择性量子阱势垒，发射极/集电极势垒等将建模和合并。 这些努力应该导致QQWW器件结构和焦平面驱动和传感电路的实现，在QWW探测器可访问的所有光谱范围内产生显著增强的性能。我们对MQW结构中的自发脉冲和对IR辐射的频率响应的研究也将继续和扩展。为了更好地评估这种操作模式在配置更高性能的探测器和焦平面方面的潜力。这种尖端技术在国家一级的重要性，以及格鲁吉亚州、康奈尔大学和加州大学洛杉矶分校高素质的工作人员和学生的密切参与，将继续对知识的进步产生重大影响，物理和工程教育将通过为科学界提供领先的年轻科学家，为国家的科学和技术基础做出重大贡献。 合作还将确保有效地转移到商业和政府实验室的新兴高科技应用。 拟议研究的结果将大大提高对探测器的理解，并为下一代探测器奠定基础。 此外，所提出的结构的实现将对诸如用于逻辑、长波IR数字数据传输或振荡器应用以及成像应用的超快电子器件等领域产生直接影响。

9809746PereraThe proposed project involves research on novel multi-quantum-well (MQW) concepts, intraband processes and IR detector operating leading to significant improvements in focal plane quality, and to potential applications in high-performance infrared imaging systems. Under the previous NSF program, emphasis was placed on photo-emissive homojunction detector formats for detection in the far infrared (FIR). These studies led to the successful development of the new family of FIR detectors, with record values of wavelength cutoff. For optimum operation at shorter wavelengths (LWIR-VLWIR), quantum-well IR photodetectors (QWIP's), which can be bandgap engineered for more selective spectral response, are preferred.Recent analyses summarized in this proposal have demonstrated that when operated in the steady-state photoconductive mode, IR QWIP detectors undergo an initial transient during which extensive redistribution and depletion of carriers in the well may occur. The number of wells contributing signal current decreases rapidly and responsivity and detectivity fall significantly, so that the full potential of such detectors cannot be realized. In collaboration with scientists at other universities (Cornell, NRC and UCLA) and national laboratories (JPL and U.S. Army Research lab) this problem will be addressed by exploring operation of the detector in a transient rather than a steady-state mode. Our initial thrust will be to experimentally study and model the transient IR behavior of prototype LWIR-VLWIR QWIP detectors, and to established the time-dependent operational physics of IR response in the steady-state mode. The role of intraband levels, well-doping, barrier parameters, emitter/collector structures, etc. in influencing transient values of IR response and dark current will be investigated. Time-varying operational bias conditions for re-fill of wells and periodic extraction of signal current will be devised. Extending on recent analysis of transient modes of detection and of space-charge distribution in multi-layer GaAs/AlGaAs structures, studies on the frequency and bias dependence of sensor response will be continued, with the aim of establishing optimum operation parameters. Optimized designed features, well-doping profiles, energy-selective QW barriers, emitter/collector barriers, etc. will be modeled and incorporated. These efforts should lead to the achievement of QWIP device architectures and focal plane drive and sensing circuits yielding significantly enhanced performance over all spectral ranges accessible to QWIP detectors.Our studies of spontaneous pulsing in MQW structures and the frequency response to IR radiation will also be continued and extended, in order better to assess the potential of this operation mode in configuring higher performance detectors and focal planes.The high national importance of this cutting-edge technology, and the close involvement of highly qualified staff and students at Georgia State, Cornell and UCLA will continue to impact significantly on advancing knowledge, and physics and engineering education making a significant contribution to the nation's science and technology base by supplying the scientific community with leading young scientists. The collaborations will also ensure effective transfer to emerging high-tech applications both in commercial and government laboratories. The results of the proposed research will vastly improve the understanding of detectors and form the basis for the next generation of detectors. In addition, realization of the proposed structures, will have an immediate impact on areas such as ultrafast electronic devices for logic, long wavelength IR digital data transmission or oscillator applications and in imaging applications.***