Strained germanium photonic crystal membranes for scalable and efficient silicon-based photonic devices

硅在电子产品中无处不在，是世界上最广泛利用的半导体材料，供应充足且价格低廉。尽管硅在电子学上取得了成功，但从根本上说，它的发光能力是有限的。这是由于其所谓的间接带隙，这意味着电子不会轻易地通过产生光子而失去能量。相反，在GaAs和InP等直接带隙化合物半导体中，电子很容易失去能量，从而产生光子。因此，这种半导体被广泛应用于光发射器，包括激光器和发光二极管。然而，化合物半导体的生产成本要高得多。因此，人们强烈希望能够在硅基平台上生产光学高效的直接带隙半导体。该项目旨在通过开发一种全新的方法在硅上直接制造锗带隙层来解决这一基本限制。锗可以很容易地生长在硅上，并且具有更接近于直接的带隙。从理论上预测，将锗晶体拉伸2%（拉伸），将成为直接带隙半导体。事实证明，生产稳定的高应变锗层在技术上具有挑战性。我们将使用我们最近发现的离子注入方法来克服这一挑战，以产生稳定的高拉伸应变锗层。这种层提供了在锗中实现创纪录光学效率的潜力。利用这些层，我们将展示光学增益和激光在光子晶体纳米腔在中红外使用全族四基系统。这种电子和光子能带结构与应变工程的结合，为硅基激光器的开发提供了一个阶梯式的变化，具有强大的开发潜力，可以扩大和改造医疗、环境和工业应用的传感器。

Silicon is ubiquitous for electronics and the most widely exploited semiconductor in the world available in plentiful and cheap supply. In spite of its success in electronics, silicon is fundamentally limited in terms of its ability to produce light. This is due to its so-called indirect band gap which means that electrons cannot easily lose energy by producing photons. In contrast, in direct band gap compound semiconductors such as GaAs and InP electrons can very easily lose energy resulting in the production of photons. Consequently, such semiconductors are widely exploited in light emitters including lasers and light emitting diodes. However, compound semiconductors are much more expensive to produce. Hence there is a strong desire to be able to produce optically-efficient direct band gap semiconductors on a silicon-based platform. This project aims to resolve this fundamental constraint by develop an entirely new approach to fabricating direct band gap germanium layers on silicon. Germanium can be readily grown on silicon and has a band gap that is much closer to being direct. It has been theoretically predicted that by straining the germanium crystal by >2% (tensile), it will become a direct band gap semiconductor. Producing stable highly strained germanium layers has proven to be technologically challenging. We will overcome this challenge using our recently discovered ion-implantation method to generate stable high tensile strained germanium layers. Such layers offer the potential to achieve record optical efficiencies in germanium. Using these layers we will demonstrate optical gain and lasing in photonic crystal nanocavities in the mid-infrared using an all group-IV based system. This combination of electronic- and photonic band structure and strain engineering offers a step-change in developing lasers on silicon with strong exploitation potential to scale-up and transform sensors for medical, environmental and industrial applications.