Date of Award

2019

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Department

Physical Sciences

First Advisor

Dr Tomasz Ochalski

Abstract

Nanowires (NW) /nanopillars (NP) offer the possibility of reducing the mismatch of III-V semiconductor materials grown on different substrates such as Si, SiN, SiO2 and are hence being considered potential candidates for coherent light sources in optoelectronics technologies. The difference between NPs and NWs lies in the growth process. The NPs are site-controlled using a patterned mask, while the NWs use a self-catalysed such as gold or Ga-droplet.. In this dissertation, the emission properties of GaAs/AlGaAs (core-shell and core-multishell) and InGaAs (unpassivated and passivated with InGaP) nanolasers have been studied with excitation powers above and below the lasing threshold at different temperatures. Both nanolasers showed a reduction of carrier decay time with excitation power. On the other hand, the spectral intensity increased with the excitation power, suggesting transition from spontaneous to stimulated emission. In particular, time-resolved photoluminescence spectra for GaAs/AlGaAs NWs reported a shift towards longer wavelength of the longitudinal modes for temperatures below 225 K. This phenomenon is caused by the increment of the material refractive index during the recombination process. Finally, the physical properties of the lasing modes have also been analysed for both samples. Helical modes are propagating inside InGaAs NPs, while multiple longitudinal and transverse modes are resonating inside the GaAs/AlGaAs NWs. Helically propagating modes allow high refractive index between interface with low refractive contrast due to the near-90 degree angle of the incident light at the interface NP-Si.

Comments

Thesis prepared in association with Tyndall National Institute.

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Access Level

info:eu-repo/semantics/openAccess

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