Quantum light emitting diodes

 

The importance of the development of solid-state lighting was recognised in 2014 by the Nobel Prize in Physics. The next generation of this technology harnesses the quantum nature of the light they emit, facilitating many new applications; provably secure communications, sub-diffraction limit imaging and lithography, and low-impact microscopy of biological systems, amongst others. We are currently investigating 2D material heterostructures, produced by the National Graphene Institute, as quantum light emitting diodes (QLEDs). Success will deliver a disruptive technology providing a practical quantum light source for a variety of applications.

 

Nanoscale properties of materials are often radically different from those that we witness at the macroscopic level. This opens exciting avenues of research exploiting these new behaviours. The discovery of graphene is perhaps the most famous example of this; isolating single atomic sheets of carbon produces a material with unprecedented mechanical and electronic properties. In the last few years research into atomically-thin materials has moved beyond graphene, investigating analogous systems with other advantages, such as semiconducting systems.

 

Quantum LED

Semiconducting two dimensional materials have the potential to revolutionise modern optoelectronics. Light emitting diodes that are just a few atoms thick have already been made, and a whole range of different devices that interface light and electronics is expected to follow. These include photodiodes, lasers, optical memories and signal processors. There is an outstanding problem present that is preventing advancement of these technologies, which is the efficiency with which light can be extracted from and fed into these new materials. Light radiated from these materials travels in all directions, with only a small fraction directed in a useful manner. On the other hand, their extreme thinness means that they are mostly transparent, letting the majority of light incident on them pass through unimpeded. The solution to both of these problems is the same; to place the material at the centre of an optical cavity, made using a photonic crystal.

Photonic crystals are arrays of reflective nanostructures, best known for being responsible for the vibrant colours on a butterfly’s wings. They can be used to guide light in specific directions, or trap it in a particular location. We are producing photonic crystals that have been carefully designed to optimise the optical properties of two dimensional materials. The primary challenge is that these materials are usually applied to the surface of a device, and most photonic crystals require the optically active element to be embedded in the centre of them. We are pursuing novel designs of crystals providing a platform for these materials to be applied on to.

 

The technology resulting from this work has the potential to have impact on a number of fields, and to seed the development of a whole range of new device structures. Information communications technologies are moving towards all-optical solutions; information is encoded on light, which can then be routed, processed and sent over long distances along fibres without converting it back into electronically encoded information. The all-optical approach has huge bandwidth and power saving advantages and devices containing two dimensional materials could dominate this market. There is also a potential to create photonic circuits, in which light is directed around microprocessors, with these materials used both as light sources and detectors. Such circuits are finding a wide variety of important applications, from lab-on-a-chip medical diagnostic devices, to efficient signal processors.