Room Temperature Terahertz Quantum Cascade Lasers on Silicon Substrates

电磁频谱的THz部分具有许多潜在的应用，包括肿瘤学（皮肤癌成像），安全成像，THz带宽光子学，生产监控和天文学。英国中国一直是太赫兹研究的先驱国家之一，也是开发该技术的先驱国家之一，包括TeraView，QMC Instruments和Thruvision在内的多家公司。目前，大多数商业成像和光谱系统使用昂贵的飞秒激光器与光电导天线，从根本上限制了功率输出到微瓦级。如果要开发并行、快速、高性能的成像和/或光谱系统，几乎所有上述应用都需要具有超过10 mW输出功率的室温源。虽然由于半导体的间接带隙，Si和Ge中的电子和空穴的带间复合是低效的，但是子带间跃迁为诸如THz频率的低能辐射提供了激光器的替代路径。量子级联激光器形式的子带间单极激光器已经使用III-V族材料进行了演示。功率高达248 mW，在10 K已被证明在太赫兹频率，但由于极性光学声子散射和相关的减少子带间的寿命，随着温度的增加，这样的设备只能在低温下工作。以前的工作是在p型Si/SiGe量子级联激光器上进行的，但由于大的非抛物性和大的有效质量，（0.3 ~ 0.4 m_0），因此很难设计出10 cm^-1以上的显著增益。在该方案中，我们建议使用纯Ge量子阱设计和L-谷电子的n型Si的第一个实验演示，基于量子级联激光器生长在硅衬底上。我们证明，低有效的0.118 m_0和长的非极性寿命的Ge/SiGe系统中潜在地提供接近的值在GaAs太赫兹量子级联激光器在4 K，也可能允许300 K操作。此外，与GaAs器件相比，廉价且成熟的可用Si工艺技术将允许THz量子级联激光器的成本至少降低100倍。这种器件可以进一步发展成垂直腔发射器（即VCSEL），用于并行成像应用或与Si光子集成，以实现THz带宽电信。最后，我们提出了光泵浦结构，具有宽带可调谐性的潜力，更高的输出功率和更高的工作温度比太赫兹量子级联laser.This计划汇集了建模和设计工具集在利兹大学与CVD生长的专业知识在沃里克大学结合在格拉斯哥大学的SiGe器件的制造和测量专业知识，提供国际领先的研究。我们有许多工业合作伙伴（AdvanceSis，Kelvin Nanotechnology和TeraView），他们为研究提供直接的开发路径。成功的室温量子级联激光器是太赫兹应用的许多新市场的一项使能技术，包括肿瘤学（皮肤癌成像）、安全成像、生产监控、蛋白质组学、药物发现和天文学。

The THz part of the electromagnetic spectrum has a number of potential applications which include oncology (skin cancer imaging), security imaging, THz bandwidth photonics, production monitoring and astronomy. The U.K. has been one of the pioneering countries in THz research but also in the exploitation of the technology with a number of companies including TeraView, QMC Instruments and Thruvision. At present most commercial imaging and spectroscopy systems use expensive femtosecond lasers with photoconductive antenna which fundamentally limits the power output to the microWatt level. Virtually all the applications referenced above require room temperature sources with over 10 mW of output power if parallel, fast, high performance imaging and/or spectroscopy systems are to be developed.While interband recombination of electrons and holes in Si and Ge are inefficient due to the indirect bandgap of the semiconductors, intersubband transitions provide an alternative path to a laser for low energy radiation such as THz frequencies. Intersubband unipolar lasers in the form of quantum cascade lasers have been demonstrated using III-V materials. Powers up to 248 mW at 10 K have been demonstrated at THz frequencies but due to polar optical phonon scattering and the associated reduction in intersubband lifetimes as the temperature is increased, such devices only operate at cryogenic temperatures. Previous work has been undertaken on p-type Si/SiGe quantum cascade lasers but due to large non-parabolicity and large effective mass (0.3 to 0.4 m_0) in the valence band, significant gain above 10 cm^-1 is difficult to engineer.In this proposal, we propose to use pure Ge quantum well designs and L-valley electrons for the first experimental demonstration of a n-type Si-based quantum cascade laser grown on top of a Si substrate. We demonstrate that the low effective of 0.118 m_0 and long non-polar lifetimes in the Ge/SiGe system potentially provide gain close to values demonstrated in GaAs THz quantum cascade lasers at 4 K and also potentially allow 300 K operation. Further the cheap and mature available Si process technology will allow at least a x100 reduction in the cost of THz quantum cascade lasers compared to GaAs devices. Such devices could be further developed into vertical cavity emitters (i.e. VCSELs) for parallel imaging applications or integrated with Si photonics to allow THz bandwidth telecoms. Finally we propose optically pumped structures which have the potential for broadband tunability, higher output powers and higher operating temperatures than THz quantum cascade lasers.This programme has brought together the modelling and design toolsets at Leeds University with the CVD growth expertise at Warwick University combined with the fabrication and measurement expertise of SiGe devices at Glasgow University to deliver internationally leading research. We have a number of industrial partners (AdvanceSis, Kelvin Nanotechnology and TeraView) who provide direct exploitation paths for the research. Successful room temperature quantum cascade lasers are an enabling technology for many new markets for THz applications including oncology (skin cancer imaging), security imaging, production monitoring, proteomics, drug discovery and astronomy.