GaAs-Based Quantum Dot Emitters for Telecomms and Broadband Applications

This thesis details InAs/GaAs quantum dots (QD) as light emitting media for gallium arsenide (GaAs) based bilayer laser devices for optical communication and dot-in-well (DWELL) superluminescent devices for broadband applications.
The first three experimental chapters detail particular properties of QD bilayers, where the strain interactions between two closely stacked QD layers are engineered for the sole aim of extending the emission wavelength of QDs towards the 1550 nm of the telecom window. In view of this, the first experimental chapter compares laser devices utilising single QD layers with 5x InGaAs cap layers, 5x bilayer QDs with GaAs cap layers, in order to highlight the significantly better performance of bilayer laser devices in achieving long wavelength emission.
In the second experimental chapter, further optimization of the growth parameters of InGaAs capped sample is explored. Room-temperature ground-state lasing at 1420 nm and electroluminescence at 1515 nm are observed and discussed. Under high-bias conditions, asymmetric broadening of peaks in the laser gain spectra are observed, extending positive net modal gain from the devices to beyond 1500 nm. The origin of this broadening is discussed.
In the third experimental chapter, bilayer QD lasers operating in the excited state at wavelengths that span the O-band are demonstrated. An increase in K-factor limited modulation bandwidth from QD lasers operating in the excited state is predicted. This is due to a reduction in carrier transport and scattering times whilst maintaining high peak modal gain.
In the last experimental chapter, a comparison of growth conditions, photoluminescence measurements, atomic force microscopy measurements and device characteristics affecting 1200-1300 nm DWELL structures with a view to their optimization for broadband applications are explained.