Condensed Matter Physics Seminar

Dr Tom Badcock, Manchester University

Friday 11 October 2013, 1500-1600
C1 Physics Building

"The remarkable optical properties of InGaN quantum wells"

Optoelectronic devices incorporating InGaN quantum wells are now firmly established in the marketplace, with 'white' LED torches and Blu-Ray DVD systems being two of the most well-known examples. The high optical efficiency (~70 %) of blue InGaN quantum wells is particularly surprising in view of the large (MV/cm) polarisation fields and relatively poor crystalline quality of the material. It is widely accepted that carrier localisation effects are instrumental in determining the optical performance of the material, yet the details of the localisation mechanism have received surprisingly little attention. In this talk, I will therefore focus on the spectroscopy and carrier dynamics of InGaN quantum well structures, with particular emphasis on those designed to emit at ~450 nm - the 'pump' wavelength for a 'white' LED. These measurements, which are performed over a wide range of excitation densities, provide insight into the recombination mechanisms and may therefore be useful in determining the physical origins of the 'efficiency droop' problem which plagues all InGaN-based LEDs.

LEDs emitting linearly polarised light may be achieved by growing the InGaN quantum well structures on non or semi-polar crystal planes. Like their polar counterparts, these structures have the potential to dramatically improve the efficiency of display technology. I will discuss our optical studies of a variety of non-polar quantum well structures, highlighting the advantages, disadvantages and puzzles that alternative growth orientations present.