Abstract
In this thesis, the surface morphologies and optical characteristics of type-II GaSb quantum ring (QR) structures and its related device applications are investigated. By changing Sb/background As flux ratios during the post-growth Sb soaking procedure, either fully quantum-dot (QD) or QR morphologies can be obtained. The intense luminescence of GaSb QR structures is observed due to the increasing electron-hole wave function overlapping and more surrounding electron shells over the QRs. To further improve the luminescence intensities of the type-II QRs, coupled QRs separated by thin GaAs spacer layers are proposed. With 5 nm GaAs spacer layers, both stronger photoluminescence (PL) intensity and larger PL blue shift are observed, which are attributed to the larger number of electrons accumulated in the thin GaAs spacer layer resulted from improved electron confinement. With further reducing the GaAs spacer layer to 2 nm, the PL intensity of the sample is even more intense than a single-period type-I InAs quantum dots (QDs). Similar with coupled QRs, InGaAs-capped QR structures have provided additional electron confinement to enhance the luminescence intensity. By using In0.15Ga0.85As capped QRs embedded in GaAs PIN diode, a wavelength-tunable light-emitting device from 1332 to 1252 nm is fabricated, which demonstrates room-temperature 1.3 u electroluminescence can be easily achieved by using the type-II InGaAs-capped GaSb QR structure.