Spectroscopic studies of III-V semiconductors in two, one and zero dimensions
Sammanfattning: In this thesis, spectroscopic studies of quantum wells (QWs), quantum wires (QWRs) and quantum dots (QDs) in III-V semiconductors are presented. The electronic structure of these low-dimensional structures have been studied by absorption, photocurrent, electroreflectance, photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. The band alignment of GaAs pseudomorphically grown on InP is investigated. The absorption of a single GaAs/InP QW is measured and compared to a calculated spectrum obtained with the effective mass theory (EMT). The results are consistent with a type II alignment. Both theory and experiment give an absorption of the order of 1%. The formation of interface layers during the growth of single bi-layers of GaAs and GaInAs in InP is studied by PL and EMT calculations. Incorporation of As gives a red- shift of the PL, interpreted as an increased effective QW width. The As adsorbed on the growing surface is shown to be the primary source for the As incorporation at the second interface. An AlGaAs/GaAs QWR structure grown on a V-grooved substrate is characterised using transmission electron microscopy (TEM) and cathodoluminescence (CL). The different quantum structures in the sample give spectrally separated luminescence peaks, which are identified by CL. This allows PLE and time-resolved PL studies of the carrier transfer involved in the excitation of the QWR. The vertical QW connected to the QWR is found to be the main channel for the excitation. QDs produced in the Stranski-Krastanow growth mode are studied in different materials systems : InAs in GaAs, InAs in InP and InP in GaInP. Controlled positioning of the QDs is achieved by selective nucleation on pre-growth patterned substrates. The electronic structure of one single InP QD is investigated by micro PL techniques: PL, PLE and TRPL. The single QD is shown to emit several PL lines, due to a reduced relaxation rate. The different spectral components have line widths of about 1 millielectronvolt, to be compared with the life time broadening which is 1 microelectronvolt.
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