| The development of small, power-efficient lasers underpins many of the technologies that we utilise today. Semiconductor nanowires are promising for miniaturising lasers to even smaller dimensions. III-V semiconductors, such as Gallium Arsenide (GaAs) and Indium Phosphide (InP), are the most widely used materials for optoelectronic devices and so the development of nanowire lasers based on these materials is expected to have technologically significant outcomes.;This PhD dissertation presents a comprehensive study of the design of III-V semiconductor nanowire lasers, with bulk and quantum confined active regions. Based on the design, various III-V semiconductor nanowire lasers are demonstrated, namely, GaAs nanowire lasers, GaAs/AlGaAs multi-quantum well (MQW) nanowire lasers and InP nanowire lasers. These nanowire lasers are shown to operate at room temperature, have low thresholds, and lase from different transverse modes. The structural and optoelectronic quality of nanowire lasers are characterised via electron microscopy and photoluminescence spectroscopic techniques. Lasing is characterised in all these devices by optical pumping. The lasing characteristics are analysed by rate equation modelling and the lasing mode(s) in these devices is characterised by threshold gain modelling, polarisation measurements and Fourier plane imaging.;Firstly, GaAs nanowire lasers that operate at room temperature are demonstrated. This is achieved by determining the optimal nanowire diameter to reduce threshold gain and by passivating nanowires to improve their quantum efficiency (QE). High-quality surface passivated GaAs nanowires of suitable diameters are grown. The growth procedure is tailored to improve both QE and structural uniformity of nanowires. Room-temperature lasing is demonstrated from individual nanowires and lasing is characterised to be from TM01 mode by threshold gain modelling.;To lower threshold even further, nanowire lasers with GaAs/AlGaAs coaxial multi-quantum well (MQW) gain regions are investigated. The TE01 mode, due to its polarisation and excellent overlap with the gain region, is predicted to lase in these nanowire heterostructures. Through gain/loss calculations, important design criteria, such as the optimal well thickness to minimise the threshold carrier density and the optimal number of QWs to minimise the threshold fluence are determined. Based on the design, MQW nanowire heterostructures containing eight uniform coaxial GaAs/AlGaAs MQWs are grown. Room-temperature lasing is demonstrated from individual nanowires at a threshold fluence that is two times lower compared to the bulk GaAs nanowire lasers. Lasing is also verified to be from TE01 mode by polarisation measurements.;Lastly, a mode characterisation technique based on imaging the polarisation dependent far-field emission pattern of nanowire lasers is presented. To demonstrate this technique, InP nanowire lasers are used, because of their excellent structural characteristics. The InP nanowire lasers are designed to lase from different guided modes by varying the nanowire diameter. The experimentally obtained polarisation dependent far-field profiles match very well with numerical simulations and enable unambiguous identification of the lasing mode(s) in nanowire lasers.;Overall, this thesis presents extensive modelling of nanowire lasers, which is supported by experimental results. The modelling will provide a useful reference for developing novel nanoscale lasers and improving the performance of current nanowire lasers. |
