Terahertz quantum cascade lasers based on interface roughness engineering in InGaAs/InAlAs heterostructures on InP

本研究的目的是展示和研究基于新型InGaAs基有源区的太赫兹量子级联激光器。有迹象表明，使用这种新设计的激光器将工作在室温附近；太赫兹QCL在如此高温下的工作还没有得到证实，这将代表着太赫兹仪器的革命性进步，为太赫兹研究和应用开辟了新的可能性。建议的有源区是InP上的InGaAs/InGaAs应变补偿材料系统。这一材料体系的两个组成部分都是InP上成熟的InGaAs合金家族的成员。利用分子束外延技术，将In含量小于0.53的InGaAs的压应变与In含量大于0.53的InGaAs的张应变进行补偿，可以实现任意低导带偏移量的应变补偿结构。该系统在太赫兹准分子激光器中的应用已在一项专利中得到了描述。InGaAs/InGaAs材料系统的优点是量子阱中的电子有效质量比GaAs/AlGaAs小。由于更高的激光增益与更小的电子有效质量相关，所提出的太赫兹激光器预计将具有大约2.3倍的增益，并能够在比目前最先进的GaAs/Al0.15Ga0.85As器件高出至少100K的温度下工作。在太赫兹量子级联激光器中，应变补偿的InGaAs材料系统相对于晶格匹配的InGaAs/InAlAs(或InGaAs/GaAsSb)材料系统的优点是可以在130-150 meV的范围内选择合适的最佳导带偏移量，与InP上匹配的InGaAs/InAlAs或InP上匹配的InGaAs/GaAsSb的高导带偏移量520 meV或360 meV相比，这些改进将使我们能够创造出可以在近室温下工作的太赫兹半导体激光器。最后，我们注意到，与其他被建议改善太赫兹量子级联激光器温度性能的方法不同，所提出的方法从根本上偏离了现有的太赫兹QCL方法，但它的优势在于它依赖于成熟的生长技术和材料系统。

The objective of this research is to demonstrate and investigate terahertz quantum cascade lasers based on a novel InGaAs-based active region. Indications are that lasers using this new design will operate near room-temperature; operation of THz QCLs at such high temperatures has not yet been demonstrated and would represent a revolutionary advance for terahertz instrumentation, opening new possibilities in terahertz research and applications.The proposed active region is the InGaAs/ InGaAs strain-compensated material system on InP. Both components of this material system are members of the well-established InGaAs alloy family on InP. By compensating the compressive strain of the InGaAs with In content less than 0.53 with the tensile strain of the InGaAs with In content greater than 0.53, strain-compensated structures with arbitrarily low conduction band offset can be realized using molecular beam epitaxy. The application of this system for THz QCLs has been described in a patent disclosure.The advantage of InGaAs/ InGaAs material system over GaAs/AlGaAs is the smaller electron effective mass in the quantum wells. Because of the higher laser gain associated with smaller electron effective mass, the proposed terahertz lasers are expected to have approximately 2.3 times higher gain and be able to operate at temperatures at least 100 K higher than is possible with the current state-of-the art GaAs/Al0.15Ga0.85As devices. Furthermore, the smaller effective mass in the proposed devices is expected to result in reduced interface roughness scattering and higher electron mobility that will further improve their performance.The advantage of the strain-compensated InGaAs material system over the lattice-matched InGaAs/InAlAs (or InGaAs/GaAsSb) material systems on InP for terahertz quantum cascade lasers is the possibility to choose the appropriate optimal conduction band offset in the range of 130 to 150 meV, in contrast to the high conduction band offset of 520 meV in the lattice matched InGaAs/InAlAs on InP or 360 meV in the lattice matched InGaAs/GaAsSb on InP.We expect that these improvements will allow us to create terahertz semiconductor lasers that can operate at near room temperature. We finally note that, unlike other approaches that are being suggested to improve the temperature performance of terahertz quantum cascade lasers, the proposed approach is a radical departure from established THz QCL approaches, but has the advantage that it relies on well-established growth techniques and material systems.