The type-I to type-II band alignment transition in InAlAsAs/AlGaAs/GaAs self-assembled quantum dots (QDs) is investigated when the Al-composition in QDs and barrier are changed. In particular, the In0.46Al0.54As/Ga0.46Al0.54As/GaAs QDs show unique optical properties. The PL peak energy has a blue-shift of >40 meV when the laser intensity increases by four orders of magnitude, indicating a type-II band alignment of the QDs. The formation of the type-II band alignment is explained by that the quantum-confinement effect pulls up the minimum electron energy level in the QDs and the Γ→X transition in the Ga0.46Al0.54As barrier. The time-resolved PL (TRPL) spectrum of QDs at peak wavelength exhibits a double-component decay behavior, suggesting the possibility of type-I and type-II band alignment coexistence in this QD sample. The continuum state of the QDs is also investigated. Emission associated with the continuum states of the QDs is directly observed in PL spectra. The PL excitation (PLE) and TRPL spectra reveal an efficient carrier relaxation from the AlGaAs barrier into the InAlAs QD ground state via the continuum states. The carrier recombination in the continuum states can compete with that in the QDs due to the long recombination lifetime in the type-II QDs. This feature of continuum state emission can not be observed for normal InGaAs/GaAs QDs with the type-I band structure.
Baolai Liang, Diana L. Huffaker, Yuriy I. Mazur, Morgan Ware, Gregory J. Salamo, Linlin Su, Ying Wang, and Qinglin Guo, "Optical characteristics of InAlAs/GaAlAs/GaAs quantum dots (Conference Presentation)," Proc. SPIE 10114, Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XIV, 101140N (Presented at SPIE OPTO: January 31, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2251605.5395679969001.
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