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巨大社会影响的领域具有商业潜力。拟议的工作将创建一个新的设备，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生物成像新系统和癌细胞检测等领域的启用组件。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允许系统具有比传统选择产生中红外光子的系统更高的灵敏度。预期的高速（20 GHz）调制能力也为在非吸收大气窗口中建立自由空间光学链路提供了可能性。这种链路可以用来取代或增强微波频率点对点通信信道。这项工作还将带来其他社会效益。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，并将通过同行审查的文献和会议传播。所提供的资金将允许本科生和研究生的研究项目进行。PI还致力于推进STEM教育，并在伊利诺伊州的各种REU/RET计划期间为高中学生和教师提供研讨会。PI还致力于妇女和代表性不足的群体的教育，项目资金的一部分将用于支持一名女研究生。这是本研究计划的目标，设计，制造和测试一种新的设备架构，用于产生中红外和更长波长的相干辐射。晶体管注入的量子级联激光器被提出作为一个3端设备，允许独立的控制跨位于异质结双极晶体管的反向偏置结和注入电流的幅度，使用正向偏置发射极-基极结控制的量子级联区域的字段。级联结构场的独立控制稳定了从根本上影响激光器操作的参数，如状态能量和寿命。这种方法提供了优于2端量子级联激光器的几个优点，2端量子级联激光器是用于产生中红外相干辐射的现任解决方案。首先，在所提出的器件中，自由载流子吸收较低，因为p-基极和n-集电极的级联区和周围部分都在基极-集电极结的耗尽区内。由于自由载流子吸收是长波长下内部损耗的关键因素，因此阈值电流密度预计将较低，斜率效率和壁插效率均较高。另外，因为级联区域中的场可以固定在提供相邻威尔斯中的能级之间的最佳谐振耦合和稳定的能态寿命的值，所以作为注入电流的函数的增益预期更稳定并且具有更好的线性。较高的驱动电流不会由于量子态的场相关未对准和状态寿命的修改而导致增益降低。最后，由于小的基极电流被用来控制设备的操作，在多千兆赫频率范围内的调制预计是可能的。该设备的成功演示有可能在中红外波长到太赫兹频率设备和这些设备的应用中创造新的研究领域。

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.