Quantum GaN-O-Photonics

技术进步导致了诸如膝上型计算机、移动的设备和全球定位系统等电子设备的可用性。为了提高性能，现代技术已经遵循了将组件封装以减小商业设备的整体尺寸的路径。随着这一趋势的发展，我们现在已经达到了可以在最小尺度上控制物质的地步：单个原子。正是在这个新的物理学领域，非常规效应发生了：当我们处理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。一个全新的影响范围发生，并可以创建具有新功能的设备：量子信息革命似乎触手可及。一个非常令人兴奋的研究领域集中在纳米结构的研究上，其尺寸为0.000000001 m。这样的小结构可以用来控制光的单个粒子：单个光子。传统光源在很宽的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。如果我们能够存储编码在单光子上的信息，我们就可以以光速传输它，并保证安全通信。单光子发射器也可应用于成像和医学传感。不幸的是，许多单光子源在非常低的温度下工作，这需要使用液氦，这对于现实世界的应用来说是昂贵且不方便的。一种称为氮化镓（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，该晶体中的缺陷可以充当单光子发射器，嵌入GaN基质中的氮化铟镓（InGaN）纳米结构也可以。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，将这些发射器纳入实际设备是非常具有挑战性的。晶体中的发光体往往在晶体中的任意位置形成，因此很难确保器件中包含一个最佳位置的单个发光体，并且很难确保光按照应用要求以高效率向所需方向发射。在本项目中，我们将开发能够控制发光体形成位置的技术，并将这些位置控制的发射器与有效地从器件提取光并将其引导到期望方向的结构集成。我们将创建光提取结构与电荷载流子到发射器中的电注入集成的设备。这意味着我们将能够使用外加电压来驱动单光子发射或改变发射光子的波长（或颜色）。我们将采取的改善光提取的方法使用的技术很容易融入标准制造程序。我们将在单光子发射器下面放置类似镜子的结构;在它们上面的晶体表面上，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，相对于其他可能的技术，这种方法还具有额外的优点：它避免了蚀刻GaN晶体，这可能会损害器件性能，并且它还对从单光子发射器获得非常特定的波长提出了不太严格的要求。金属环还兼作电注入的触点。总的来说，这为创造新的量子技术提供了一条可扩展的、强大的途径，这解决了英国政府在先进材料和制造方面的优先事项，也是在现实生活中实现量子发射器的关键一步。

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.