Broadening of submonolayer CdSe sheets in CdSe/ZnSe superlattices studied by x-ray diffraction

Kyutt, R. N.; Торопов, А. А.; Sorokin, S. V.; Shubina, T. V.; Ivanov, S. V.; Karlsteen, M.; Willander, Magnus

doi:10.1063/1.124379

Cited by 52 publications

(25 citation statements)

References 13 publications

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“…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. From the widely studied system InAs/GaAs, which has a similar lattice mismatch, the importance of surface segregation for intermixing is well known.…”

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confidence: 99%

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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“…Original Paper based matrices has been studied extensively [7][8][9][10]. Both material combinations have a strong lattice mismatch: ∆a/a = +7.9% for CdSe with respect to BeTe, and 6.8% with respect to ZnSe.…”

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Raman analysis of embedded monolayers and quantum dots

Geurts

Wagner

2005

Physica Status Solidi (b)

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We demonstrate the potential of resonant Raman spectroscopy from vibration modes for the analysis of embedded monolayers and quantum dots. As representative systems, we present results for CdSe, embedded either in BeTe or in ZnSe. The vibration spectra reflect a distinctly different behaviour. For CdSe in BeTe, they reveal atomically sharp interfaces, especially when the interface bonds are chosen to be Cd -Te. In addition, the vibration modes reflect the onset of quantum dot formation. They are described by ab initio calculations. In contrast, in case of CdSe quantum dots in ZnSe, the vibration spectra are explained in terms of ternary (Cd,Zn)Se modes with increasing Cd content for increasing nominal CdSe coverage. Thus, they reveal a noticeable interfacial intermixing on the scale of a few monolayers.

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“…The following assumptions were employed: CdSe QDs were considered as a Zn 1−x Cd x Se QW of Gaussian prole with x = 0.85−0.95 at maximum (QW bottom) and the broadening parameter was chosen within 57 MLs in analogy with CdSe QDs in ZnSe matrix, studied accurately by using X-ray diraction [10] and transmission electron microscopy [11]. Zn 1−x Cd x Se/ZnSe band osets were determined based on a model-solid theory [12], taking account of ≈ 40% elastic stress accommodation that occurs during CdSe QDs formation [13].…”

Section: Theoretical Calculationsmentioning

confidence: 99%

CdSe/ZnCdSe Quantum Dot Heterostructures for Yellow Spectral Range Grown on GaAs Substrates by Molecular Beam Epitaxy

Gronin¹,

Sorokin²,

Kazanov

et al. 2014

Acta Phys. Pol. A

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This paper reports on theoretical calculations and fabrication by molecular beam epitaxy of wide-gap IIVI heterostructures emitting in the true yellow range (560600 nm) at room temperature. The active region of the structures comprises CdSe quantum dot active layer embedded into a strained Zn1−xCdxSe (x = 0.2−0.5) quantum well surrounded by a Zn(S,Se)/ZnSe superlattice. Calculations of the CdSe/(Zn,Cd)Se/Zn(S,Se) quantum dot quantum well luminescence wavelength performed using the envelope-function approximation predict rather narrow range of the total Zn1−xCdxSe quantum well thicknesses (d ≈ 2−4 nm) reducing eciently the emission wavelength, while the variation of x (0.20.5) has much stronger eect. The calculations are in a reasonable agreement with the experimental data obtained on a series of test heterostructures. The maximum experimentally achieved emission wavelength at 300 K is as high as 600 nm, while the intense room temperature photoluminescence has been observed up to λ = 590 nm only. To keep the structure pseudomorphic to GaAs as a whole the tensile-strained surrounding ZnS0.17Se0.83/ZnSe superlattice were introduced to compensate the compressive stress induced by the Zn1−xCdxSe quantum well. The graded-index waveguide laser heterostructure with a CdSe/Zn0.65Cd0.35Se/Zn(S,Se) quantum dotquantum well active region emitting at λ = 576 nm (T = 300 K) with the 77 to 300 K intensity ratio of 2.5 has been demonstrated.

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Broadening of submonolayer CdSe sheets in CdSe/ZnSe superlattices studied by x-ray diffraction

Cited by 52 publications

References 13 publications

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

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

Raman analysis of embedded monolayers and quantum dots

CdSe/ZnCdSe Quantum Dot Heterostructures for Yellow Spectral Range Grown on GaAs Substrates by Molecular Beam Epitaxy

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