The Transistor-Injected Quantum Cascade Laser, An Improved Coherent Mid-IR Source

中红外波长的高功率光子源在具有重大社会影响的领域具有商业潜力。这项拟议的工作将创造一种新的设备，可用于环境(温室气体检测、地下水和废水监测)、工业(化学过程传感和汽车排放传感器)和国土安全(爆炸物检测)应用的超敏感系统。该设备还可以用作正在开发的用于生物成像的新系统的使能部件，并可用于癌细胞检测等领域。在所有这些应用中，“晶体管注入量子级联激光器”预期的更高输出功率应该会使系统比使用传统选项产生中红外光子的系统具有更高的灵敏度。预期的高速(20 GHz)调制能力也为在非吸收大气窗口中产生自由空间光链路提供了可能性。这种链路可以用来取代或增强微波频率点对点通信通道。这项工作还将提供其他社会效益。所获得的基本知识将纳入伊利诺伊大学关于化合物半导体器件的课程，并将通过同行评议的文献和会议进行传播。提供的资金将使本科生和研究生的研究项目得以继续进行。PI还致力于推进STEM教育，并在伊利诺伊州的各种REU/RET计划期间为高中生和教师提供研讨会。PI还致力于女性和代表性不足群体的教育，项目资金的一部分将用于支持一名女性研究生。这项研究计划的目标是设计、制造和测试一种用于产生中红外和更长波长的相干辐射的新型设备架构。晶体管注入量子级联激光器是一种三端器件，它允许对位于异质结双极晶体管反向偏置结中的量子级联区的场和注入电流的幅度进行独立控制，利用正向偏置发射极-基极结来控制注入电流的幅度。级联结构场的独立控制稳定了从根本上影响激光器运行的状态能量和寿命等参数。这种方法比双端量子级联激光器有几个优点，后者是产生中红外相干辐射的现有解决方案。首先，在所提出的器件中，自由载流子吸收较低，因为p基区和n基区的级联区域和周围部分都在基区-集电极结的耗尽区内。由于自由载流子吸收是导致长波长内损耗的主要因素，阈值电流密度预计会更低，而斜率效率和壁塞效率都会更高。此外，由于级联区中的场可以固定在提供相邻井能级和稳定能态寿命之间的最佳共振耦合的值，因此作为注入电流的函数的增益预计将更稳定并且具有更好的线性。较高的驱动电流不会由于与场相关的量子态的不对准和态寿命的改变而导致增益降低。最后，由于使用了较小的基本电流来控制设备的运行，因此有望在几千兆赫的频率范围内进行调制。这种设备的成功演示有可能在中红外波长、太赫兹频率设备以及这些设备的应用方面开创新的研究领域。

High-power photon sources at mid-infrared wavelengths have commercial potential in areas having large societal impact. The proposed work will create a new device that can be used in ultra-sensitive systems for environmental (greenhouse gas detection, ground water and wastewater monitoring), industrial (chemical process sensing and automotive emission sensors), and homeland security (explosive detection) applications. The device could also be used as an enabling component in new systems being developed for biological imaging and in areas such as cancer cell detection. In all of these applications, the higher output powers expected with the "transistor-injected quantum-cascade laser" should allow systems with greater sensitivity than systems where mid-infrared photons are generated with conventional options. The anticipated ability to modulate at high speed ( 20 GHz) also opens the possibility of producing free-space optical links in non-absorbing atmospheric windows. Such links could be used either in place of or to augment microwave-frequency point-to-point communication channels. This work will also provide other societal benefits. Basic knowledge gained will be incorporated into courses at the University of Illinois on compound semiconductor devices, and will be disseminated through peer-reviewed literature and at conferences. The funding provided will allow undergraduate and graduate research projects to proceed. The PI is also committed to advancing STEM education, and has provided seminars to high school students and teachers during various REU/RET programs at Illinois. The PI is also committed to the education of women and underrepresented groups, and a portion of the project funds will be used to support a female graduate student.It is the objective of this research program to design, fabricate, and test a novel device architecture for the generation of coherent radiation at mid-infrared and longer wavelengths. The transistor-injected quantum cascade laser is proposed as a 3-terminal device that allows independent control of the field across a quantum cascade region located in the reverse-biased junction of a heterojunction bipolar transistor and the amplitude of the injected current, controlled using the forward biased emitter-base junction. Independent control of cascade structure field stabilizes parameters such as state energy and lifetime that fundamentally impact laser operation. This approach provides several advantages over the 2-terminal quantum cascade laser, which is the incumbent solution for the generation of mid-IR coherent radiation. First, free carrier absorption is lower in the proposed device because both the cascade region and surrounding portions of the p-base and n-collector are within the depletion region of the base-collector junction. Because free-carrier absorption is a key contributor to internal loss at long wavelength, threshold current densities are projected to be lower and both slope efficiency and wall-plug efficiency higher. Additionally, because the field in the cascade region can be fixed at a value that provides optimal resonant coupling between the energy levels in adjacent wells and stable energy state lifetimes, the gain as a function injected current is expected to be more stable and have better linearity. Higher drive currents will not cause gain reduction due to field-related misalignment of quantum states and modification of state lifetimes. Finally, because a small base current is used to control the operation of the device, modulation in the multi-gigahertz frequency range is expected to be possible. Successful demonstration of this device has the potential to create new areas of research in both mid-infrared wavelength through terahertz frequency devices and in the applications for those devices.