Development of Advanced GaAs Based Quantum Dot Devices

This thesis details research on the development of ~1.3μm quantum dot (QD) devices. QD devices which are theoretically ideal for the realisation of temperature insensitive lasers. A method to measure the recombination coefficients in a semiconductor laser is developed, and the role of Auger recombination in the realisation of temperature insensitive lasers is discussed.
Moreover, due to a broad spectral linewidth and strong state-filling effects, QD structures are promising for application as broadband light sources.
It is reported that the Auger recombination coefficient decreases with increasing device temperature, as measured by several complicated experimental techniques. In chapter 2, a simple analysis method (small signal modulation) to measure all of the recombination coefficients is introduced and discussed. In chapter 3, experimental data based on the small signal modulation technique is analysed. Which shows that all of the recombination coefficients, including the Auger coefficient, are a function of temperature and modulation doping in QD lasers.
Following on from chapter 3, in chapter 4 the dynamic characteristic (differential carrier lifetime) of a 3μm-ridge QD laser device fabricated from commercial QD material is investigated. The modelled GS peak gain as a function of current density is determined based on the recombination coefficients, the random population model and the measured gain (via the
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Hakki-Paoli method). Then, by comparing the modelled GS gain to the experimental results, the carrier thermal escape parameter is determined. Finally in chapter 4, the variation of the Auger coefficient is explored to investigate the possibility of a temperature independent current density.
The selective intermixing technique can be used in order to achieve broadband light source devices. In chapter 5, the intermixing method is introduced based on both quantum well and quantum dot structures. Then, a number of different capping materials on samples with different active region structures are discussed based on photoluminescence measurements from intermixed structures. The potential for selective area intermixing of an integrated device with a TiO2 and SiO2 cap annealed on a p-doped sample is demonstrated at the end of the chapter.
Finally, in chapter 6, two integrated devices are fabricated based on this TiO2 and SiO2 cap. These devices demonstrate a broad emission bandwidth, and by applying a fast Fourier transform to the spectra in order to determine the point spread function of the instrument, and application of the Rayleigh criterion for resolution, an estimation of the resolution in an OCT system is made.