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

硅在电子产品中无处不在，是世界上开发最广泛的半导体，供应充足，价格低廉。尽管硅在电子领域取得了成功，但它在发光方面的能力从根本上受到限制。这是由于其所谓的间接带隙，这意味着电子不能轻易地通过产生光子而失去能量。相比之下，在直接带隙化合物半导体如GaAs和InP中，电子可以非常容易地损失能量，导致光子的产生。因此，这种半导体被广泛地用于包括激光器和发光二极管的光发射器中。然而，化合物半导体的生产成本要高得多。因此，强烈希望能够在硅基平台上生产光学有效的直接带隙半导体。本项目旨在通过开发一种全新的在硅上制造直接带隙锗层的方法来解决这一基本限制。锗可以容易地生长在硅上，并且具有更接近于直接的带隙。理论上预测，通过使锗晶体应变>2%（拉伸），它将成为直接带隙半导体。生产稳定的高应变锗层已被证明是技术上的挑战。我们将克服这一挑战，使用我们最近发现的离子注入方法，以产生稳定的高拉伸应变锗层。这样的层提供了在锗中实现记录光学效率的潜力。使用这些层，我们将使用全IV族系统演示中红外光子晶体纳米腔中的光学增益和激光发射。这种电子和光子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台阶式的变化，具有强大的开发潜力，可扩大和改造传感器，用于医疗，环境和工业应用。

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.