Optical Properties Of InAs/AaAs Self-Organized Quantum Dot Molecule Nanomaterials

Semiconductor quantum dot?QD?nanomaterials not only have unique physical properties,but also have huge potential for many novel optoelectronic device applications.In this dissertation research,the optical properties of a series of InAs QD molecule?QDM?are studied by photoluminescence?PL?and time-resolved photolumenescence?TRPL?spectroscopy.The research includes three sections.?1?The optical properties of bilayer InAs/GaAs QDs is studied as a functin of the GaAs spacer layer thickness of 30 ML,40ML,and 50 ML respectively.The PL spectra measured at low temperature show bimodal profile for all samples,indicating an effective carrier transfer from SQDs to TQDs.The PL peak position?Emax?,the full width at half maximum?FWHM?,and the integral intensity of the TQDs are measured for three samples with respect to the excitation intensity and the temperature.The results indicate that the carrier transfer efficiency becomes lower as the GaAs spacer thickness becomes larger.It is further confirmed by the TRPL measurement.?2?The QDM structure composed of bilayer InAs/GaAs QD-pairs with a thin Al_0.5Ga_0.5As barrier insertion in the middle is investigated.The small SQDs PL intensity of the InAs QDM indicates an effective carrier transfer from SQDs to TQDs.After inserting the thin Al_0.5Ga_0.5As barrier layer,both SQDs and TQDs show blue-shifted emission,and the SQDs PL intensity increase relatively.Therefore,the Al_0.5Ga_0.5As barrier layer reduce the carrier transfer.The variations of the PL peak energy,FWHM,integral intensity,and intensity ratio with respect to the temperature and the excitation intensity indicate that the carrier transfer in this coupled QDM structure depended on temperature as well as excitation intensity.The TRPL measurements show that the carrier tunneling time increases from 0.38 ns to 0.77 ns after inserting the Al_0.5Ga_0.5As barrier layer.This agrees well with the theoretical calculation by using the semiclassical WKB equation.?3?Optical properties of InAs/GaAs+InAs/GaAsSb QDMs are investigated for the GaAs0.85Sb0.15 and GaAs0.75Sb0.25 capping layer,respectively.First,the type II band alignment for InAs/GaAs0.85Sb0.15 and InAs/GaAs0.75Sb0.25 QDs is verified.Then,at the temperature of T=10K,PL spectra of the QDMs show a multimodal behavior with increasing the excitation laser intensity.The multimodal peaks in the PL spectra are corresponding to different carrier recombination channels,indicating that the hybrid QDM structures have different internal carrier generation,transfer,and recombination dynamics from ordinary InAs/GaAs QDMs.