Abstract
In this thesis, the surface morphologies and optical characteristics of quantum dot (QD) samples grown under different conditions are investigated. Similar surface morphologies and photoluminescence (PL) spectra are observed for the InAs/GaAs QDs grown with both the As shutter always-opened and initially-opened procedures, while no uniform QD formation are observed with the As shutter initially-closed procedure. The phenomenon is attributed to the In droplet formation at the GaAs surface under the As-deficient condition. Additionally, compared with the standard QD growth mode on the device performance of the InAs/GaAs quantum-dot infrared photodetectors (QDIPs), better QD size uniformity is obtained for the QDs grown by migration-enhanced (ME) growth mode. Longer QDIPs detection wavelengths and reduced normal incident absorption are observed for the device with QDs grown by ME growth mode. For InGaAs QDs with different In compositions, larger QD sizes are observed with decreasing In compositions. Also observed is the PL peak energy blue shift with decreasing In composition, which is attributed to the increase of bandgap with increasing Ga composition. Uniform InGaAs QDs with dot densities up to 7x1010 cm-2 are observed for the samples with InGaAs coverage 5 and 6 ML. For the sample with 7 ML InGaAs coverage, QD density reduction and PL wavelength blue shift are observed. Finally, with proper growth condition, high-quality QD structure could be obtained with mere 50 nm GaAs buffer. Compared with GaAs regrown layer, the regrowth of GaAsSb material on patterned GaAs substrates has demonstrated much smooth surfaces.