EAGER: Electrothermal Investigation of Damped Bloch Transport at Extremely High Fields in Wide Bandgap Semiconductor Materials and its Exploitation for New Paradigms in...

电子设备运行的基础是电荷的运动，这是电流流动的来源。因此，了解电荷在块状材料中、跨材料界面或沿材料界面以及通过更复杂的结构传输的性质，不仅是开发和优化当今电子设备所必需的，而且对于创新进程和在尺寸、速度、功率和其他性能指标方面提供卓越功能的全新设备的概念来说，也确实至关重要。在极大电场的影响下，最近的理论分析预测，在新兴的纤锌矿III-氮化物材料体系中，微观水平上的电荷运动呈现出与在其他半导体晶体中所观察到的完全不同的全新特征。具体地说，大量电子的综合影响，其个别轨迹在微观水平上主要是振荡的，共同导致宏观负差分电阻，可用于各种原始的高速、高功率器件应用。这项拟议的工作将在微观层面上对这种新的电荷传输模式及其在宏观层面上的影响产生透彻的理解，并提供一个坚实的理论框架，有可能产生毫米波和太赫兹电子器件的全新范例。拟议的研究结果将通过会议报告、在技术期刊上发表，并纳入佐治亚理工学院研究生和本科生的课程。佐治亚理工学院(GT)是一所为科学和工程领域中代表性不足的群体提供教育的领先机构。它的工程学院在授予妇女和少数民族工程学学位方面处于全国领先地位，并将积极鼓励代表人数不足的群体参与拟议的研究。证据表明，在纤锌矿III-氮化物材料系统中，在极高的场强下，存在一种全新的、未知的电荷传输模式，这对高功率毫米波和太赫兹(THz)电子设备具有令人兴奋的意义。在只有宽禁带半导体材料才能承受的高场强下，电子穿过布里渊区所需的时间在某些情况下可能接近甚至低于热电子的特征散射时间。在这个极高的场域中，电荷传输的特征是衰减的Bloch振荡，粒子在真实空间中的速度和轨迹主要是振荡的，零星的中断是由动量随机化的与声子的碰撞造成的，这是自相矛盾的，导致了净向前运动。这与教科书中低场强下电荷传输的图景截然不同，在课本图景中，电子的瞬时速度主要是热的和随机定向的。此外，由于阻尼型Bloch振荡，参与Bloch输运的电子呈现负的微分漂移速度，这与其他已知的负微分电阻(NDR)机制的根本不同之处在于，在最大场强的极限下，漂移速度渐近于零(而不是某个有限的值)。这种负的微分漂移速度可以激发各种各样的电荷域不稳定性，这些不稳定性可以被用来产生高功率毫米波和太赫兹信号。该工作基于解析和半解析方法以及电热全带系综蒙特卡罗模拟，对布洛赫输运现象、相关的电荷域不稳定性及其对器件应用的影响进行了深入的理论研究。

Fundamental to the operation of electronic devices is the motion of charge, which is the origin of electrical current flow. Understanding the nature of charge transport in bulk materials, across or along material interfaces, and through even more complex structures is therefore not only requisite for the development and optimization of present-day electron devices, but is indeed critical for the process of innovation and for the conception of entirely new devices offering superior functionality in terms of size, speed, power, and other performance metrics. Under the influence of extremely large electric fields, recent theoretical analysis predicts that charge motion at the microscopic level in the emerging wurtzite III-nitride material system takes on an entirely new character, radically dissimilar to that which has been observed in other semiconductor crystals. Specifically, the combined influence of a large number of electrons, whose individual trajectories are predominantly oscillatory at the microscopic level, collectively leads to a macroscopic negative differential resistance which can be exploited for diverse original high-speed, high-power device applications. The proposed work will generate a thorough understanding of this new mode of charge transport at the microscopic level, its implications at the macroscopic level, and provide a solid theoretical framework with the potential to engender entirely new paradigms for millimeter-wave and terahertz electronic devices. Results of the proposed research will be disseminated through conference presentations, publication in technical journals, and incorporated into courses taught at Georgia Tech at both the graduate and undergraduate levels. Georgia Tech (GT) is a leading institution for the education of underrepresented groups in science and engineering. Its College of Engineering leads the nation in engineering degrees awarded to women and minorities, and the participation of underrepresented groups in the proposed research will be encouraged proactively. Evidence is presented for a fundamentally new and unexplored mode of charge transport in the wurtzite III-nitride material system at extremely high field strengths, with exciting implications for high-power millimeter-wave and terahertz (THz) electronics. At the high field strengths which only wide bandgap semiconductor materials can sustain, the time required for electrons to traverse the Brillouin zone can in some cases approach and even fall below the characteristic scattering time for hot electrons. In this extremely high field regime, charge transport is characterized by damped Bloch oscillation, for which particles velocities and trajectories in real space are predominantly oscillatory, with sporadic interruption by momentum-randomizing collisions with phonons which, paradoxically, lead to a net forward motion. This is very different from the textbook picture of charge transport at lower field strengths, in which electrons instantaneous velocities are predominantly thermal and randomly-oriented. Moreover, electrons participating in Bloch transport exhibit a negative differential drift velocity as a result of damped Bloch oscillation which is critically different from other known mechanisms for negative differential resistance (NDR) in that the drift velocity tends asymptotically towards zero (rather than some finite value) in the limit of largest field strengths. This negative differential drift velocity can excite a wide variety of charge domain instabilities that may be exploited for the generation of high-power millimeter-wave and THz signals. The proposed effort represents a thorough theoretical investigation of the phenomenon of Bloch transport, the associated charge domain instabilities, and its implications for device applications, based on analytic and semi-analytic methods, as well as electrothermal full-band ensemble Monte Carlo simulation.