研究目的
To explore the evolution of the topographical and optical properties of InAs QDs and the corresponding wetting layer (WL) on the GaAs surface near the onset of QD formation.
研究成果
The evolution of InAs QDs and WL near the onset of QD formation was investigated, revealing the coexistence of QD, WL, and precursor peaks in PL spectra. The precursor peak is attributed to 2D InAs islands small enough to localize excitons, while the WL peak is due to larger InAs islands under high compressive strain. The sudden transfer of material from WL to QDs near the onset of QD formation was observed, contradicting the understanding of constant WL thickness during QD formation.
研究不足
The study focuses on the subcritical region of InAs coverage for transition from a 2D to a 3D growth mode, which may not fully represent the behavior at higher coverages. The very low growth rate used may also limit the generalizability of the findings to other growth conditions.
1：Experimental Design and Method Selection:
InAs QDs were grown on a GaAs (001) substrate using molecular beam epitaxy (MBE) with a very low growth rate of InAs to observe the evolution of QDs and WL near the onset of QD formation.
2：Sample Selection and Data Sources:
Samples were named based on the InAs coverage, e.g., a sample where 1.52 ML InAs was deposited has been named S1.52. AFM and PL measurements were performed to study the surface morphology and optical properties.
3：52 ML InAs was deposited has been named SAFM and PL measurements were performed to study the surface morphology and optical properties.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: RIBER32 MBE UHV chamber, arsenic valve cracker source, epiready semi-insulating GaAs (001) substrates, atomic force microscope (AFM), continuous-wave diode-pumped solid-state 532 nm excitation laser, TE-cooled silicon photodetector.
4：Experimental Procedures and Operational Workflow:
InAs QDs were grown at 460 °C with a 0.005 ML/s growth rate. The substrate was not rotated and the growth stage was tilted by 5° from its optimum position. Postgrowth annealing was performed after each layer of InAs QD growth.
5：005 ML/s growth rate. The substrate was not rotated and the growth stage was tilted by 5° from its optimum position. Postgrowth annealing was performed after each layer of InAs QD growth.
Data Analysis Methods:
5. Data Analysis Methods: PL spectra were deconvoluted into Gaussian components to analyze the QD, WL, and precursor peaks. The power dependence of the PL peaks was also analyzed.
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