Post-growth annealing of CdS crystals grown by physical vapor transport

Chen, K.-T.; Zhang, Y.; Egarievwe, Stephen U.; George, M. A.; Bürger, A.; Su, Ching‐Hua; Sha, Yi‐Gao; Lehoczky, S. L.

doi:10.1016/0022-0248(95)00513-7

Cited by 13 publications

(6 citation statements)

References 25 publications

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“…16À18,52À54 Other defects, such as Cd I with an energy level of 1.68 eV above the valence band, S I with 2.18 eV from the conduction band, and two anti-site defects with energy levels of 1.5 and 2.0 eV above the valence band, form the deep levels in CdS and contribute mainly to the red band luminescence which was observed by Yasuhiro et al and was probably inaccurately attributed to cadmium interstitial. 55 Chen et al also found that a cadmium-rich sample showed a peak centered around 2.07 eV, 56 which was attributed to sulfur vacancies, but based on our calculations, this peak could actually originate from the cadmium interstitials. Chen et al also performed annealing under a cadmium atmosphere and reported a 1.48 eV emission, which likely arises from the anti-sites, in agreement with our calculations.…”

Section: Resultsmentioning

confidence: 99%

Dynamics of Bound Exciton Complexes in CdS Nanobelts

et al. 2011

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Intrinsic defects such as vacancies, interstitials, and anti-sites often introduce rich luminescent properties in II-VI semiconductor nanomaterials. A clear understanding of the dynamics of the defect-related excitons is particularly important for the design and optimization of nanoscale optoelectronic devices. In this paper, low-temperature steady-state and time-resolved photoluminescence (PL) spectroscopies have been carried out to investigate the emission of cadmium sulfide (CdS) nanobelts that originates from the radiative recombination of excitons bound to neutral donors (I(2)) and the spatially localized donor-acceptor pairs (DAP), in which the assignment is supported by first principle calculations. Our results verify that the shallow donors in CdS are contributed by sulfur vacancies while the acceptors are contributed by cadmium vacancies. At high excitation intensities, the DAP emission saturates and the PL is dominated by I(2) emission. Beyond a threshold power of approximately 5 μW, amplified spontaneous emission (ASE) of I(2) occurs. Further analysis shows that these intrinsic defects created long-lived (spin triplet) DAP trap states due to spin-polarized Cd vacancies which become saturated at intense carrier excitations.

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Section: Resultsmentioning

confidence: 99%

Dynamics of Bound Exciton Complexes in CdS Nanobelts

et al. 2011

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“…Their simultaneous presence fixes the Fermi level position in the upper part of the NC band gap. It is commonly recognized that the sulfur vacancy is a dominant defect in CdS because of the lowest formation energy among the intrinsic defects. , During the evaporation of the LB matrix by annealing, the sulfur vacancies can be partly filled with excess cadmium atoms; i.e., the antisite defects are formed.…”

Section: Discussionmentioning

confidence: 99%

Scanning Tunneling Spectroscopy of Free-Standing CdS Nanocrystals Fabricated by the Langmuir–Blodgett Method

Svit

Журавлев

2015

J. Phys. Chem. C

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The energy spectrum and tunneling transport through ensembles of closely packed CdS nanocrystals (NCs) obtained by the Langmuir−Blodgett (LB) method have been investigated using the scanning tunneling spectroscopy (STS) technique at room temperature. NC ensembles were obtained by annealing the solid LB matrix in a vacuum or in an ammonia atmosphere. The STS data indicate the formation of point defects attributed to an excess of Cd atoms in NC capturing tunneling electrons and the effect of the ammonia atmosphere on the defect formation process. A high density of defects arising as a result of sintering NCs that lost a protective organic shell during the migration on the substrate surface is likely to cause a band gap narrowing in NCs located near the ensemble edge. The analysis of a dependence of the zeroconduction gap value on the NC size gives evidence of a strong effect of the Coulomb interaction between the carriers located in NCs and their polarization charges in the shells on the NC energy spectrum. A dielectric constant of the shell (ε out = 10−16.5) and the energy barrier height for electrons (V 0 = 0.6−0.8 eV) were determined. The shell comprises ammonia and organic molecules, the ammonia molecules making a major contribution to the shell dielectric constant and the organic molecules determining the barrier height.

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“…CdS is a visible‐range direct semiconductor, with applications in light‐emitting diodes, photoresistors, solar cells, optically active waveguides, etc. Most research on developing new CdS‐based devices is aimed at tuning the optical properties through doping1, 2 or spatial confinement (when at least one crystalline dimension is kept below the exciton Bohr radius2, 3) but the optical properties have also been reported to change on grinding4 or annealing5–9 in undoped CdS crystals with dimensions above the confinement limit. A relationship between the optical properties and CdS polymorphism has already been suggested10, 11 and the purpose of this paper is to investigate the impact of grain size and structural defects on CdS optical properties.…”

Section: Introductionmentioning

confidence: 99%

Off‐resonance Raman analysis of wurtzite CdS ground to the nanoscale: structural and size‐related effects

Gouadec

Colomban

et al. 2011

J Raman Spectroscopy

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Different techniques were used to follow the transformation of CdS platelets during grinding and under hydrostatic pressure. X-ray diffraction and transmission electron microscopy revealed that the platelets included zinc blende (cubic) CdS nanodomains dispersed in a wurtzite (hexagonal) single-crystalline matrix. Extended grinding led to a decrease of the grain size and to a progressive transformation of the hexagonal stacking into a cubic one. The same phase transition was observed up to 9 GPa under hydrostatic pressure.Off-resonance Raman spectra collected at different stages of the transition led us to connect band groups that were usually overlooked (in resonance conditions) or considered separately. They all probe the stacking disorder and their intensity can be related to the density of stacking faults. Off-resonance Raman spectroscopy offers a way of probing the optical properties of CdS (and, more generally, layered semiconductors) as a function of the structure and of the confinement of vibrations by structural defects.

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Post-growth annealing of CdS crystals grown by physical vapor transport

Cited by 13 publications

References 25 publications

Dynamics of Bound Exciton Complexes in CdS Nanobelts

Dynamics of Bound Exciton Complexes in CdS Nanobelts

Scanning Tunneling Spectroscopy of Free-Standing CdS Nanocrystals Fabricated by the Langmuir–Blodgett Method

Off‐resonance Raman analysis of wurtzite CdS ground to the nanoscale: structural and size‐related effects

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