Study of the carrier-induced optical properties in III-V quantum confined laser nano-structures

Nanostructures with electrons quantum confined in all three spatial dimensions such as quantum dots (QDs) are considered to be artificial atoms. The optical characteristics of the artificial atoms can be engineered to create new semiconductor laser materials with desired optical properties.; In this dissertation work, the carrier-induced optical properties of the semiconductor diode lasers with an active region composed of InAs QDs are investigated. Spectral dependence of the modal gain, carrier-induced refractive index change and linewidth enhancement factor in QD lasers are the main subject of this research. The comparison between the material parameters such as differential gain (dG/dN) and differential carrier-induced refractive index (dn/dN) of the QD laser and a conventional quantum well (QW) laser of the same design is performed.; Anisotropy of the optical properties in QD and quantum dash (QDash) nanostructures is explored. This anisotropy is due to the polarization dependence of the matrix transition element in these quantum confined nanostructures. Considerations of the QDash polarization properties made it possible to tune the modal gain peak in the QDash laser up to 10 nm by varying the dash orientation in the laser cavity. An experimental study of the dependence of laser characteristics (gain and carrier-induced refractive index) on quantum dash orientation with respect to the electric field of the cavity mode was performed.; Modification of the fundamental material parameters of the QD laser structures is demonstrated by engineering the dot shape and the chemical composition of the barrier material. This QD engineering significantly improved QD laser characteristics resulting in a more than two-fold increase in the differential gain and a decrease of the linewidth enhancement factor.; Finally, a comprehensive model has been proposed to describe the linear optical properties of the QD laser structures. This model includes inhomogeneous broadening arising from QD size fluctuations and incorporates the actual electronics states. The model was used to describe the spectral dependence of the material gain, the carrier-induced refractive index, the linewidth enhancement factor, and the spontaneous emission. Comparison with the experimental results has been made, revealing the key physical processes affecting the QD carrier-induced optical properties.