Zibik E A, Grange T, Carpenter B A, Porter N E, Ferreira R, Bastard G, Stehr D, Winnerl S, Helm M, Liu H Y, Skolnick M S, Wilson L R
[1] Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK [2] Present addresses: Oclaro (Switzerland) AG, Binzstrasse 17, CH-8045 Zürich, Switzerland (E.A.Z.); Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany (T.G.); Department of Electronic & Electrical Engineering, University College London, London WC1E 7JE, UK (H.Y.L.) [3] These authors contributed equally to this work.
Nat Mater. 2009 Oct;8(10):803-7. doi: 10.1038/nmat2511. Epub 2009 Aug 16.
Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to approximately 2 ps at 30 meV (7 THz), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.
载流子弛豫是决定半导体光电器件运行效率的关键问题。由于预测量子点的激发态寿命较长，包含半导体量子点的器件有潜力克服许多基于量子阱器件的限制。例如，基于量子阱的器件（量子级联激光器）中太赫兹激光运行所需的粒子数反转从根本上受到激光能级之间有效散射的限制，这些能级在量子阱平面内形成一个连续体。在这种情况下，半导体量子点对于太赫兹器件来说是极具吸引力的替代方案，因为它们具有固有的离散能级。在此，我们展示了对处于少数太赫兹范围内跃迁能量的量子点中量子子能级间载流子弛豫的首次测量及理论描述。对于14毫电子伏特（3.4太赫兹）的能级间隔，发现量子点内弛豫时间很长（1.5纳秒），而在30毫电子伏特（7太赫兹）时则急剧下降至约2皮秒，这与我们关于载流子弛豫过程的微观理论非常吻合。我们的研究为量子点太赫兹器件的发展铺平了道路，提供了优化器件设计所需的载流子弛豫时间的基础知识。
