Investigation into semiconductor microcavity light emitting strucutres, and the assessment of InAs/GaAs quantum dots as sources for etched microstructures

Abstract

The spectral, spatial, and temporal characteristics of the spontaneous light emission process are dependent on the optical environment with which the emitter interacts. Cavity structures with dimensions of the order of the emission wavelength produce strong modifications of this optical environment and hence the spontaneous emission process of an internal emitter. Such microcavity structures possess the potential for the realisation light emitting diodes with increased efficiency, spectral purity, directionality and speed. In this thesis the emission properties of a planar microcavity LED emitting in the red region of the spectrum, and of a novel higher dimensional microcavity structure emitting in the infra-red are presented, together with an investigation into the ability of InAs/GaAs quantum dot emitters to reduce the impact of edge recombination effects in etched microcavity structures. We investigate the design and performance of planar microcavity LEDs whose emission wavelength is matched to the plastic optical fibre transmission window at 650nm. The measured electrical and optical characteristics of a fabricated device are presented, showing strong microcavity effects in the spatial and spectral emission properties. Carrier leakage, device heating, and non-optimised cavity design are all shown to play a role in determining the low efficiency (<1.5%) and low maximum output power (<1mW) of the device. We present simulation results showing the impact of cavity resonance wavelength position, source emission linewidth, and mirror properties on device efficiency. Optimised optical designs of microcavities emitting at 650nm for maximum emission efficiency into air and into a fibre with a numerical aperture of 0.5 are presented.