Indium : Light emitting diodes and beyond

Rachel A. Oliver Department of Materials Science and Metallurgy, University of Cambridge

Light emitting diodes (LEDs) exploiting (InGaN) quantum wells for light emission in the green, blue and near ultra-violet regions of the spectrum have been a huge commercial success. However, their effectiveness remains something of a mystery to researchers, since the GaN pseudo-substrates on which they are typically grown are riddled with threading dislocations which act as non-radiative recombination centres and should thus quench light emission. Some microstructural feature of the quantum wells is believed to prevent exciton diffusion to dislocation cores. In this presentation, I will explore various attempts to identify the key microstructural feature, including the problems which arise in using TEM to examine InGaN, due to the damage wrought on the sample by the electron beam. We have attempted to overcome these problems by using an alternative technique: three-dimensional atom probe (3DAP), and I will present the first 3DAP pictures of nitride samples, and show how they provide insights into the nano- and meso- scale microstructure of the InGaN quantum wells.

Whilst InGaN-based LEDs are widely available, there may be other opportunities for this material in novel devices. In the second part of my talk, I will introduce our recent work on single photon sources based on InGaN quantum dots, and discuss the challenges that the nitride materials system brings to the construction of such devices. I will demonstrate the application of InGaN quantum dots in an optically pumped blue-emitting single photon source, and discuss the potential advantages of such a source and the hurdles which still need to be overcome before a commercially viable device can be developed.