Near-field optical spectroscopy of localized excitons in strained CdSe quantum dots

Flack, F.; Samarth, N.; Nikitin, V.; Crowell, P. A.; Shi, Jianwei; Levy, Jeremy; Awschalom, D. D.

doi:10.1103/physrevb.54.r17312

Cited by 181 publications

(77 citation statements)

References 17 publications

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“…The system CdSe/ZnSe is in the center of interest because of its high lattice mismatch of about 7%, which is expected to result in self-assembled quantum dots during epitaxial growth [1][2][3][4] and its possible application for optoelectronic devices in the yellow/green/blue spectral range. Recently, a strong intermixing leading to broadened ternary quantum structures was reported by different groups, [5][6][7][8][9][10][11] but the origin of this intermixing is still under discussion.…”

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Segregation-enhanced etching of Cd during Zn deposition on CdSe quantum dots

et al. 2001

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CdSe/ZnSe quantum structures grown on GaAs͑001͒ by molecular-beam epitaxy were systematically investigated by high-resolution x-ray diffraction and high-resolution transmission-electron microscopy. Half of the initial Cd deposit redesorbs when migration-enhanced epitaxy is used instead of conventional molecular-beam epitaxy for the overgrowth of the CdSe by ZnSe. This result is explained by a segregation model accounting for an enhanced redesorption of Cd due to Cd segregation and replacement of Cd by Zn in the topmost surface layers. The observed intermixing of CdSe/ZnSe can be explained by this model. DOI: 10.1103/PhysRevB.64.193311 PACS number͑s͒: 68.35.Dv, 68.35.Fx, 81.05.Dz The system CdSe/ZnSe is in the center of interest because of its high lattice mismatch of about 7%, which is expected to result in self-assembled quantum dots during epitaxial growth 1-4 and its possible application for optoelectronic devices in the yellow/green/blue spectral range. Recently, a strong intermixing leading to broadened ternary quantum structures was reported by different groups, 5-11 but the origin of this intermixing is still under discussion. From the widely studied system InAs/GaAs, which has a similar lattice mismatch, the importance of surface segregation for intermixing is well known.12 Surface segregation was also observed in the system CdSe/ZnSe ͑Refs. 5 and 10͒ but the rather symmetrical depth profiles of composition found by highresolution transmission-electron microscopy ͑HRTEM͒ are commonly interpreted in terms of interdiffusion.11 However, this results in Cd diffusion constants, which are orders of magnitude higher than those determined by annealing experiments. 9,11 In order to clarify the role of surface segregation, we have varied the method of ZnSe-cap-layer deposition under controlled conditions. Conventional molecularbeam epitaxy ͑MBE͒ and migration-enhanced epitaxy ͑MEE͒ have been used for cap-layer growth. The situation at the growing surface is changed drastically in the latter case due to alternate supply of group-II and -VI elements. The influence of the overgrowth parameters is systematically studied by high-resolution x-ray diffraction ͑HRXRD͒, grazing incidence x-ray diffraction ͑GIXRD͒, and HRTEM.HRXRD as well as HRTEM give information about the incorporated amount of CdSe. Additionally, HRTEM provides knowledge on the depth distribution of Cd, which is hardly accessible by HRXRD due to the small scattering volume of CdSe quantum-dot structures. Structural information on extremely thin layers at the sample surface can be obtained by GIXRD despite the small scattering volume. This enables to investigate the structural properties of CdSe quantum dots before overgrowth by ZnSe.The samples were grown at 280°C on GaAs͑001͒ substrates in a twin-chamber MBE system ͑EPI 930͒ equipped with Zn, Se, and Cd elemental sources for II-VI layer growth. The CdSe layers were deposited by MEE at 0.029 ML per second and are embedded in a 40-50-nm-thick ZnSe buffer layer and a 20-25-nm ZnSe cap layer. The intend...

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Segregation-enhanced etching of Cd during Zn deposition on CdSe quantum dots

et al. 2001

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“…Further modulation of the electronic structures and control of the transport dynamics of carriers in CdSe nanostructures are very important to optimize the optoelectronic properties. It has been demonstrated that the carrier and exciton transport dynamics can be effectively tuned in CdS/CdSe superlattices and core/shell nanostructures such as CdTe/ CdSe [4] and ZnSe/CdSe [5], due to the alignment of their band structures and bandgap offset. Most recently, it has been experimentally illustrated that the colloidal core/ crown CdSe/CdS nano-platelet based heterostructures can act as efficient exciton concentrators [6].…”

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Outermost tensile strain dominated exciton emission in bending CdSe nanowires

Liao

et al. 2014

Sci. China Mater.

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Artificial modulation of electronic structures and control of the transport dynamics of carriers and excitons in CdSe nanowire are important for its application in optoelectronic nanodevices. Here, we demonstrate the aggregative flow of excitons by bending CdSe nanowires. The bending strain induces spatial variance of bandgap, and the energy bandgap gradient will result in the flow of excitons towards the bending outer edge of CdSe nanowire. The exciton emission energy shows a uniform redshift in the bending region due to the aggregative flow of excitons, and the energy redshift increases linearly with increasing the strain at the outer edge of the CdSe nanowire. Our results show an effective method to drive, concentrate, and utilize the excitons in CdSe nanowires, which provides a guide for the design of high performance and flexible optoelectronic nanodevices.

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“…[1][2][3] The optical properties of such islands have been mainly studied by incoherent methods. [4][5][6][7] Driven by the search for blue-green-emitting semiconductor materials, the fabrication [8][9][10][11][12][13] and optical characterization [14][15][16][17][18] of self-assembled II-VI islands have recently been the subject of intensive research. Only little is known about the coherent properties of these structures, giving information about exciton scattering and biexciton formation.…”

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