Quantum GaN-O-Photonics

技术进步导致了笔记本电脑、移动设备和全球定位系统等电子设备的出现。为了提高性能，现代技术遵循了组件小型化的道路，以减小商业设备的整体尺寸。顺着这一趋势，我们现在已经达到了可以在最小的尺度上控制物质的点：单个原子。正是在这个新的物理学领域，非传统效应发生了：当我们处理只由几个原子组成的结构时，或者当我们操纵单个电子电荷时，物理学遵循量子力学描述的规则。一系列全新的效应正在发生，具有新功能的设备可能被创造出来：量子信息革命似乎指日可待。一个非常令人兴奋的研究领域集中在纳米结构的研究上，纳米结构是尺寸在0.000000001m量级的实体。这样的小结构可以用来控制光的单个粒子：单个光子。传统光源在大角度范围内发射大量光子，主要用于照明和成像。在单光子水平上控制光的能力在技术上具有挑战性，但非常有趣。如果我们可以存储在单个光子上编码的信息，我们就可以以光速传输它，并保证安全通信。单光子发射器在成像和医学传感方面也有应用。不幸的是，许多单光子源工作在非常低的温度下，这需要使用液氦，这对于现实世界的应用来说既昂贵又不方便。一种名为氮化镓(GaN)的材料提供了克服这些限制的机会。GaN是一种半导体晶体，晶体中的缺陷可以作为单光子发射器，就像嵌入在GaN基质中的氮化铟(InGaN)纳米结构一样。这种纳米结构可以在室温下发射单光子，波长范围非常宽。然而，将这些发射器整合到实际设备中是非常具有挑战性的。它们往往在晶体中的随机位置形成，这使得很难确保设备包含一个位置最佳的单一发射器，以及应用程序所需的光在所需方向上以高效率发射。在这个项目中，我们将开发允许我们控制发射器形成位置的技术，并将这些现场控制的发射器与有效地从设备中提取光并将其引导到所需方向的结构相结合。我们将创建这样的器件，其中光提取结构与向发射器中注入电荷载流子的电注入集成在一起。这意味着我们将能够使用施加的电压来驱动单光子发射或改变发射的光子的波长(或颜色)。我们将采取的改进光提取的方法使用的技术很容易被纳入标准制造程序。我们将在单光子发射器下面放置镜面结构；在它们上面，在晶体表面上，我们将放置微小的金属环，它可以像透镜一样，将光引导到应用系统中。除了相对容易制造之外，与其他可能的技术相比，这种方法还有其他优点：它避免了对GaN晶体的刻蚀，这可能会损害器件的性能，而且它对从单光子发射器获得非常特定的波长的要求也不那么严格。金属环还兼具电注入触点的双重作用。总体而言，这为创造一种新的量子技术提供了一条可扩展的、强大的途径，该技术解决了英国政府在先进材料和制造方面的优先事项，并代表着在现实生活设备中实施量子发射器方面向前迈出的关键一步。

Technological advances have led to the availability of electronic devices like laptops, mobile devices and global positioning systems. In order to increase performance, modern technology has followed the path of miniaturising the components to reduce the overall size of commercial devices. Following this trend, we have now reached the point where matter can be controlled at the smallest scale: the single atom. It is in this new realm of physics that unconventional effects take place: when we deal with structures composed of just a few atoms or when we manipulate single electronic charges, the physics follows rules described by quantum mechanics. A completely new range of effects take place and devices with novel functionalities can be created: the quantum information revolution seems to be within reach.A very exciting research field focuses on the study of nanostructures, entities whose dimensions are of the order of 0.000000001m. Such small structures can be used for controlling single particles of light: single photons. Conventional light sources emit a large number of photons in a wide angular range and are mainly used for lighting and imaging. The ability to control light at the single-photon level is technologically challenging but tremendously interesting. If we can store information encoded on single photons, we can transfer it at the speed of light with a guaranteed secure communication. Single-photon emitters also find applications in imaging and medical sensing. Unfortunately, many single-photon sources operate at very low temperatures, which require the use of liquid helium, which is expensive and inconvenient for real-world applications. A material called Gallium Nitride (GaN) offers opportunities to overcome these limitations. GaN is a semiconductor crystal, and defects in that crystal can act as single-photon emitters, as can indium gallium nitride (InGaN) nanostructures embedded in a GaN matrix. Such nanostructures can emit single photons at room temperature, across a very wide range of wavelengths. However, incorporating these emitters into practical devices is very challenging. They tend to form at random locations in the crystal, which makes it hard to ensure that a device contains an optimally-positioned single emitter and that the light is emitted in the desired direction with high efficiency, as required for applications.In this project, we will develop technologies which allow us to control where an emitter forms, and integrate those site-controlled emitters with structures which extract the light from the device efficiently and channel it in a desired direction. We will create devices where the light extraction structures are integrated with the electrical injection of charge carriers into the emitter. That means that we will be able to use an applied voltage to either drive the single-photon emission or to alter the wavelength (or colour) of the emitted photon.The approach we will take to improving light extraction uses technologies that are easily incorporated into a standard manufacturing routine. We will put mirror-like structures underneath the single-photon emitters; above them, on the crystal surface, we will place tiny rings of metal, which can act like a lens, directing the light into the application system. In addition to being relatively easy to manufacture, relative to other possible technologies, this approach has additional advantages: it avoids etching the GaN crystal, which can damage device performance, and it also places less stringent requirements on achieving a very specific wavelength from the single-photon emitter. The metallic ring also doubles up as a contact for electrical injection. Overall, this provides a scalable, robust route to creating a new quantum technology - which addresses UK government priorities for advanced materials and manufacturing, and represents a crucial step forward in the implementation of quantum emitters in real-life devices.