Optical Properties Of Semiconductor Quantum Dots With The Type-? Band Alignment

Semiconductor quantum dots?QDs?have been investigated extensively due to the unique properties and the enormous potential for versatile electronic and photonics devices.In this research,the optical properties of type-? semiconductor QDs have been studied by photoluminescence?PL?,photoluminescence excitation spectrum?PLE?,and time-resolved photoluminescence?TRPL?technologies.The research include:1.The optical properties of In_0.46Al_0.54As/Al_0.54Ga_0.46As QDs have been investigated.At low temperature,the PL peak has a fast blueshift with increasing laser intensity,which indicates the type-? band alignment for the QDs.The broadening of QDs emission with increasing laser intensity indicates the lateral electronic coupling effect for the high density QDs.This lateral electronic coupling enables the QD PL peak to have a fast redshift and a linewidth narrowing,both beginning from the quite low temperature?35 K?.The PL decay curves show a special double exponential decay behavior,indicating the coexistence of type-? and type-? band alignment in this QD sample.2.In order to investigate continuum state of the type-? In_0.46Al_0.54As/Al_0.54Ga_0.46As QDs,PL,PLE,and TRPL have been measured.The continuum state signal is directly observed in both PL and PLE spectra.The TRPL results reveal that the carrier dynamics strongly depend on the continuum state.The long rise time of QD emission indicate that the carriers efficiently relax from AlGaAs barrier into QDs through the continuum state.The observed narrowing and fast redshift of QDs emission with increasing temperature also testify that the carrier relaxation and redistribution are through the continuum state.3.The GaAs/AlxGa1-xAs quantum dots-ring?QDR?hybrid structures,which consist of four closely spaced GaAs/AlxGa1-xAs QDs in each QDR,have been investigated as a function of the Al-composition in the AlxGa1-xAs barrier to achieve the transition from type-? to type-? band alignment.The fluctuation in QD height leads to an abnormal blueshift for the PL peak with increasing laser intensity.Therefore,long lifetime from TRPL measurement become an important feature to characterize the type-? band alignment.When Al composition increases to x=0.6,the measured lifetime and rise time are ⁶ ns and ¹70 ps,respectively.These results indicate that the type-? GaAs/AlxGa1-xAs QRs is realized at x=0.6,and the transition point from type-? to type-? band alignment is between x=0.45 and x=0.6.