Spectroscopic ellipsometry, photoluminescence and Kelvin probe force microscopy studies of CdSe nanoparticles dispersed on ZnS thin film

Sharma, Intu; Batra, Y.; Mehta, B. R.

doi:10.1063/1.4923219

Cited by 12 publications

(9 citation statements)

References 33 publications

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“…As the single crystal transforms to polycrystalline and amorphous, its permittivity changes . Note that the phenomenon of changes in permittivity corresponding to crystallographic changes has been reported for nanoparticle CdSe, nanocrystal CdSe, and nanocrystalline PbSe film …”

Section: Realization Of the Broadband Perfect Absorbermentioning

confidence: 72%

“…As the single crystal transforms to polycrystalline and amorphous, its permittivity changes. [21,22] Note that the pheno menon of changes in permittivity corresponding to crystallographic changes has been reported for nanoparticle CdSe, [23] nanocrystal CdSe, [24] and nanocrystalline PbSe film. [25] To change the permittivity of thin film PbSe by its amorphousness, we varied the sputtering power used in the PbSe deposition.…”

Section: Realization Of the Broadband Perfect Absorbermentioning

confidence: 77%

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Maximal Visible Light Energy Transfer to Ultrathin Semiconductor Films Enabled by Dispersion Control

Jung

Yoo

Kim

et al. 2019

Advanced Optical Materials

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dielectric and semiconductor [2] nanostructures. In addition, to extend absorption over a broader range of the solar spectrum, multiple semiconducting layers with different absorption bands have been used to create multijunction solar cells. [11,12] Despite such efforts, the high efficiency thin-film semiconductor absorber is still a topic of active research. The classical Yablonovitch limit [13] of maximum achievable absorption, which is based on geometrical optics, does not apply to ultrathin semiconductor absorbers. Attempts have been made to overcome the Yablonovitch limit using wave optics rather than geometrical optics. [14,15] For example, the enhancement of local density of states (LDOS) using optical resonators can exceed the Yablonovitch limit with the upper bound determined by the LDOS sum rule. [16] However, the performance of ultrathin semiconductor absorbers based on the LDOS enhancement can be limited by Ohmic losses and narrow working frequency band in optical resonators.Here, we propose a new dispersion control scheme for maximal light absorption by ultrathin semiconducting absorbers. We analyze the typical configuration of a thin-film absorber deposited on a metal substrate coated with a dielectric spacer layer and find the condition for maximal light energy transfer to the thin absorber over the entire visible spectrum. Specifically, we show that the near perfect absorption of visible light by an ultrathin film is possible when the permittivity of the absorber satisfies the ideal dispersion relation. We explain how the ideal dispersion relation can be achieved with semiconductor bandgap materials by controlling resonances. The inevitable loss, arising only from the absorption by the reflector possessing finite conductivity, can be minimized by controlling the thicknesses of dielectric spacer and absorber, resulting in typically less than 5% loss from the aluminum reflector and less than 1% from the silver reflector. As experimental verification, we fabricated ultrathin lead selenide (PbSe) absorbers on an aluminum reflector with SiO 2 spacers and controlled the dispersion of PbSe permittivity by changing the sputtering condition. We find that dispersion-controlled 9 nm thick PbSe film can reduce the reflectance averaged over the entire visible range to less than 4% and the aluminum absorption to 8% so that the absorption of visible light by an ultrathin PbSe film reaches 88% which is close to the theoretical maximum value of 95%.Increasing light absorption in an ultrathin semiconductor is critical for developing thin-film photovoltaic devices. Here, it is shown that a maximal absorption of visible light is possible through controlling the dispersion of thin-film materials. The ideal dispersion relation is determined for the permittivity of a thin film placed on a reflector with a dielectric spacer, and it is explained how the ideal dispersion relation can be realized for semiconductor materials possessing bandgaps. To experimentally verify dispersion control and maximal absorption, the permitti...

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Section: Realization Of the Broadband Perfect Absorbermentioning

confidence: 72%

Section: Realization Of the Broadband Perfect Absorbermentioning

confidence: 77%

Maximal Visible Light Energy Transfer to Ultrathin Semiconductor Films Enabled by Dispersion Control

Jung

Yoo

Kim

et al. 2019

Advanced Optical Materials

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“…The obtained spectra for real (ε 1 ) and imaginary (ε 2 ) parts of dielectric constants for ZnTe, ZnTe:O (0.02%), and ZnTe:O (0.2%) samples deposited at RT and substrate temperature of 300 °C are shown in Figure a,b and c,d, respectively. For crystalline materials, energy dependence of dielectric constant spectra, that is, ε( E ) is an exact replica of the Brillouin Zone (BZ) associated with crystal structure. , …”

Section: Resultsmentioning

confidence: 99%

“…For crystalline materials, energy dependence of dielectric constant spectra, that is, ε(E) is an exact replica of the Brillouin Zone (BZ) associated with crystal structure. 20,47 Features observed in ε(E) spectra of ZnTe are due to the edge excitons and interband critical points (CPs) and are denoted by…”

Section: Resultsmentioning

confidence: 99%

Oxygen Induced Enhanced Photoanodic Response of ZnTe:O Thin Films: Modifications in Optical and Electronic Properties

et al. 2017

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In the present work, photoanodic response of ZnTe thin films is enhanced by incorporating oxygen, which is explained by analyzing oxygen-induced modifications in structural, optical, and electronic behavior of ZnTe thin films, using detailed experimental characterizations and density functional theory (DFT) based calculations. On incorporating oxygen, the nanocrystalline character of ZnTe is increased with a change in optical properties due to absorption through sub band states and an increase in fundamental absorption edge. From DFT analysis, origin of these sub band gap states is attributed to oxygen incorporation induced electronic states and Te vacancies. Photoelectrochemical (PEC) performances of ZnTe with and without oxygen have been investigated where a change over from photocathodic response for ZnTe to enhanced photoanodic response for ZnTe:O thin films along with increased response for low energy photons is observed. These findings are explained in terms of oxygen induced modification in visible light absorption, enhanced surface area due to increased nanocrystalline character and modified electronic properties of ZnTe:O thin films. Modifications in optical properties and enhancement in PEC performance by oxygen incorporation shown in the present study may be useful for developing ZnTe-based photovoltaic devices.

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“…As NRs in the present work are fabricated using dry ICP-RIE followed by wet etching in HF, their surface properties are expected to be different in comparison to as-grown GaN epitaxial film. Any small modification in surface can alter surface potential which in turn changes the Fermi level position in the semiconductor 32 33 34 . We have performed surface potential measurements on GaN epitaxial film and NRs using KPFM technique.…”

Section: Resultsmentioning

confidence: 99%

Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes

Kumar

Heilmann

Latzel

et al. 2016

Sci Rep

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The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained.

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Spectroscopic ellipsometry, photoluminescence and Kelvin probe force microscopy studies of CdSe nanoparticles dispersed on ZnS thin film

Cited by 12 publications

References 33 publications

Maximal Visible Light Energy Transfer to Ultrathin Semiconductor Films Enabled by Dispersion Control

Maximal Visible Light Energy Transfer to Ultrathin Semiconductor Films Enabled by Dispersion Control

Oxygen Induced Enhanced Photoanodic Response of ZnTe:O Thin Films: Modifications in Optical and Electronic Properties

Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes

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