Infrared and Device Physics of Quantum Well Structures

9809746 Perera拟议的项目包括研究新的多量子井(MQW)概念、带内工艺和红外探测器操作，从而显著改善焦平面质量，并在高性能红外成像系统中潜在应用。在之前的NSF计划中，重点放在用于远红外(FIR)探测的光发射同质结探测器格式上。这些研究导致了新的FIR探测器家族的成功开发，其波长截止值达到了创纪录的水平。为了在较短波长(LWIR-VLWIR)下实现最佳工作，可以通过带隙设计获得更好的光谱响应的量子井红外光电探测器(QWIP‘s)是首选的。最近的分析表明，当红外QWIP探测器工作在稳态光导模式时，会经历一个初始的瞬变过程，在这个过程中可能会发生量子阱中载流子的广泛再分布和耗尽。提供信号电流的井数迅速减少，响应率和探测率显著下降，使得这种探测器的全部潜力无法实现。在与其他大学(康奈尔大学、国家研究中心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)的科学家的合作下，这个问题将通过探索探测器在暂态模式而不是稳态模式下的运行来解决。我们的首要任务将是对LWIR-VLWIR QWIP探测器原型的瞬时红外行为进行实验研究和建模，并建立稳态模式下红外响应的随时间变化的操作物理模型。研究了带内能级、掺杂、势垒参数、发射极/集电极结构等对红外响应和暗电流瞬变值的影响。将设计用于重新填充油井和周期性提取信号电流的时变操作偏置条件。在对多层结构中探测模式和空间电荷分布的最新分析的基础上，将继续研究传感器响应的频率和偏置关系，以确定最佳的工作参数。优化的设计特性、良好的掺杂特性、能量选择性量子波势垒、发射极/集电势垒等将被建模并纳入其中。这些努力应该会导致QWIP器件架构和焦平面驱动和感测电路的实现，从而在QWIP探测器可访问的所有光谱范围内产生显著增强的性能。我们还将继续和扩展对MQW结构中的自发脉冲和对IR辐射的频率响应的研究，以便更好地评估这种操作模式在配置更高性能探测器和焦平面方面的潜力。这种尖端技术的高度国家重要性，以及佐治亚州、康奈尔大学和加州大学洛杉矶分校高素质教职员工和学生的密切参与，将继续对知识的发展产生重大影响。物理和工程教育为国家的科学技术基础做出了重大贡献，为科学界提供了领先的青年科学家。这些合作还将确保有效地转移到商业和政府实验室中的新兴高科技应用。拟议的研究结果将极大地提高对探测器的理解，并为下一代探测器奠定基础。此外，拟议结构的实现将对用于逻辑的超高速电子设备、长波红外数字数据传输或振荡器应用以及成像应用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.***