Size-Dependent Absorption and Defect States in CdSe Nanocrystals in Various Multilayer Structures

Nesheva, D.; Levi, Z.; Aneva, Z.; Zrinscak, I.; Main, C.; Reynolds, S.

doi:10.1166/jnn.2002.148

Cited by 7 publications

(17 citation statements)

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“…An alternative approach to measure the stationary photoconductivity spectral response of a photoconductor is the constant photocurrent method (CPM). It is based on illumination of the photoconductor with a monochromatic light, varying the incident photon energies, while adjusting the number of incident photons so that the photocurrent in the sample is kept constant …”

Section: Resultsmentioning

confidence: 99%

“…The reference value of the absorption coefficient was taken from the optical spectroscopy measurements performed in our previous study . For more detailed description of the constant field and the constant photocurrent method, their physical bases, and the working equations for analysis of experimental data, the reader is referred to original and reference works and and references therein. In this context, it is of certain physical significance to test the agreement between the two methodologies with respect to the derived conclusions concerning the band structure parameters of the investigated material.…”

Section: Resultsmentioning

confidence: 99%

“…Temperature dependences of the photocurrent were obtained in the temperature range from 77 to 390 K by a Keithley 6487 Picoammeter under illumination with white light (400−750 nm, ∼30 mW/cm 2 ). Spectral photoelectrical measurements were carried out employing either the constant field method or the constant photocurrent method (CPM). ,− , The CPM method allows precise exploration of the absorption spectrum of thin films, and thus important conclusions about size-induced changes in the electronic structure of photoconductive nanocrystalline materials could be derived. The CPM measurements were carried out at room temperature.…”

Section: Methodsmentioning

confidence: 99%

“…Spectral photoelectrical measurements were carried out employing either the constant field method or the constant photocurrent method (CPM). 34,[46][47][48][49]51 The CPM method allows precise exploration of the absorption spectrum of thin films, and thus important conclusions about size-induced changes in the electronic structure of photoconductive nanocrystalline materials could be derived. The CPM measurements were carried out at room temperature.…”

Section: Sample Characterizationmentioning

confidence: 99%

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Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS₂ Quantum Dots

et al. 2010

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The transport properties of nonequilibrium (photoexcited) charge carriers in sonochemically synthesized threedimensional (3D) assemblies of AgBiS 2 quantum dots (QDs) deposited as thin films were studied. To characterize the photoconduction of quantum-confined nanocrystals close packed in thin film form, both stationary and time-resolved experiments were performed. Besides by interband electronic transitions in the bulklike part of the nanocrystals, the photoresponse of nanocrystalline films was found to be also affected to a greater extent by the crystal boundary barrier height modulation upon illumination. The surface and bulk recombination velocities were found to be comparable. Good agreement was obtained between the band gap energy determined by analysis of the photoconductivity data measured by the constant field and the constant photocurrent method (∼1.18 eV). This value is in agreement with the optical spectroscopy data. It is higher than the optical band gap of a bulk specimen of this semiconductor, due to 3D confinement effects on the charge carrier motions within individual QDs. The nonequilibrium conductivity was found to relax exponentially with a time constant of 1.67 ms, which corresponds to average lifetime of minority charge carriers (holes).

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Sample Characterizationmentioning

confidence: 99%

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Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS₂ Quantum Dots

et al. 2010

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“…By using ] on a log-log plot as a function of t, β and τ can be directly determined. The other type of non-exponential PL decay, the power-law decay has been extensively studied in amorphous and porous silicon [30][31][32][33], and it is characterized by I(t) ~ t -p . On a log-log plot of I(t) as a function of t, a power law decay results in a straight line.…”

Section: Theorymentioning

confidence: 99%

Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED

et al. 2006

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Ultrafast spectroscopy, in particular time-resolved photoluminescence, can help in the development of InGaN/GaN heterostructures for long wavelength visible emitters. In this paper, we present recent results that underscore the current understanding of two approches to achieve desired emission characteristics and recombination mechanisms in InGaN/GaN MQWs for green LEDs. Specifically, the photoluminescence decay of samples grown using two different design approaches is discussed. In one approach, samples, with high indium incorporation, were grown on a high quality AlN substrate to achieve green emission. The resulting photoluminescence decay of the green luminescence is long-lived and non-exponential. Quantitative analysis showed that the decay is non-exponential and consists of a stretched-exponential decay component, at short times, followed by a power law decay component at longer times. This non-exponential decay, resulting in significant elongation of the radiative lifetime, is indicative of inhomogeneity in the quantum wells. Thus carrier localization, in a structure with low defect density, proves to be an effective means to achieve green emission. In another approach, a piezoelectric Stark-like ladder effect is used. In this case, a methodical layer-by-layer growth homogeneity optimization process was adopted to achieve an optical transition below the electron to heavy-hole (e 1 hh 1 ) transition when the quantum well is subjected to the presence of the strong piezoelectric polarization dipole. An advantage of this approach is that it has proven successful in achieving green luminescence on conventional sapphire substrates. The resulting photoluminescence decay at 14 K of a sample grown by this approach is single exponential and shorter in duration than the decay observed in the first approach. This exponential decay further supports previous AFM studies that revealed a homogeneous active region.

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Defect states in CdSe nanocrystalline layers

Nesheva

Reynolds

Main

et al. 2005

Physica Status Solidi (a)

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Defect states and recombination processes are investigated in SiOx/nanocrystalline CdSe multilayer and composite films, and CdSe single films, using steady‐state and transient photoconductivity and thermally‐stimulated current measurements. A reduction in mobility‐lifetime product as layer thickness is reduced is assigned to increased deep defect density at the nanocrystal surface. Transient photocurrent falls rapidly at typically 0.1 µs as carriers are trapped in deep states, and then continues to fall as a power law of index close to –1. At elevated temperatures, the transient current in multilayer films falls below the steady‐state dark current. This is explained by the effect of potential barrier profiles on recombination. The density of states distribution obtained is fairly broad in multilayers and composite films while in single layer films it is noticeably peaked. Two defect bands located at 0.55 and 0.7 eV below the conduction band edge are identified, the former associated with the nanocrystal bulk and the latter with the CdSe–CdSe interface. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Size-Dependent Absorption and Defect States in CdSe Nanocrystals in Various Multilayer Structures

Cited by 7 publications

References 0 publications

Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS₂ Quantum Dots

Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS₂ Quantum Dots

Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED

Defect states in CdSe nanocrystalline layers

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Size-Dependent Absorption and Defect States in CdSe Nanocrystals in Various Multilayer Structures

Cited by 7 publications

References 0 publications

Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS2 Quantum Dots

Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS2 Quantum Dots

Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED

Defect states in CdSe nanocrystalline layers

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Product

Resources

About

Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS₂ Quantum Dots

Photoconductivity and Relaxation Dynamics in Sonochemically Synthesized Assemblies of AgBiS₂ Quantum Dots