| Ⅲ-Ⅴ group In(Ga)As/GaAs semiconductor quantum dots(QDs)nanomaterials exhibit many unique physical properties and possess great application potential in the fields of optoelectronic devices.This research investigates the effects of morphology and structure on the optical properties and photo-generated carrier dynamics for InGaAs/GaAs quantum dot chain as well as InGaAs/GaAs surface quantum dot nanomaterials by using photoluminescence(PL),photoluminescence excitation(PLE)spectroscopy,and time-resolved photoluminescence(TRPL)measurements.The research results include:(1)The optical properties of a sample with single-layer one-dimensionally-ordered InGaAs/GaAs QD-chains were investigated.It is found that the neighboring QDs are closer along the chain direction,resulting carrier tunneling inside QD-Chains.Therefore,the PL spectra exhibit an asymmetry profile and polarization behavior.Meanwhile,the high energy shoulder of the PL spectra broadens with increasing the excitation power,while the measured carrier lifetime decreases rapidly at the high energy side of the PL spectra.(2)The InGaAs/GaAs surface quantum dots(SQDs)and buried quantum dots(BQDs)are comparatively studied.Their PL spectra indicate that SQDs have a more complicated carrier recombination mechanism due to surface states in comparison with BQDs.Moreover,SQDs have higher carrier collection efficiency than BQDs at room temperature.A wide absorption band signal corresponding to the SQDs wetting layer is observed in the PLE spectrum.The temperature-dependent PL spectra indicate that the SQDs have different carrier thermal activation and repopulation mechanisms from the BQDs due to the wide absorption band of the wetting layer.(3)The influence of GaAs spacer thickness on the optical properties of InGaAs SQDs are investigated to testify the vertical coupling and carrier transfer inside three bilayer structures of BQDs and SDQs.PL and TRPL results indicate that the thinner the spacer layer,the stronger the coupling of SQDs with BQDs.In addition,the luminescence signal from the wetting layer of SQDs is observed in the PL spectra of the samples with thin spacer layer.Thewetting layer signal for SQDs is further verified by the excitation power dependent PL spectra and PLE spectra.In summary of the above experimental results,the optical properties of InGaAs QDs nanomaterials have been testified to closely correlate with their morphology and structural characteristics.By dedicated spectroscopic measurements,this research reveals some novel optical features and implied carrier dynamics for InGaAs/GaAs quantum dot chain as well as InGaAs/GaAs surface quantum dot nanomaterials.These observations have enriched our understanding for physics properties of such QD nanomaterials and will help us to exploit their applications. |
