Dynamics of electronic transitions and frequency dependence of negative capacitance in semiconductor diodes under high forward bias

Bansal, Kanika; Henini, M.; Alshammari, Marzook S.; Datta, Shouvik

doi:10.1063/1.4896541

Cited by 8 publications

(7 citation statements)

References 16 publications

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“…The signal output from the impedance analyzer is therefore the ratio of the complex EL intensity (magnitude and phase) to the complex current density or, in other words, a frequency‐dependent complex quantum efficiency. This technique has previously been used to study defect and tail states in inorganic LEDs, [ 27–29 ] but has yet to be applied to organic solar cells.…”

Section: Resultsmentioning

confidence: 99%

“…Here, we apply modulation electroluminescence spectroscopy (MELS) [ 27–29 ] to demonstrate that CT EL from both bulk and planar heterojunction small molecule OPV cells is dispersive. That is, CT emission on the high energy side of the electroluminescence (EL) spectrum exhibits a different modulation response (i.e., magnitude and phase as a function of modulation frequency, in direct analogy to impedance spectroscopy) than CT emission on the low‐energy side of the EL spectrum.…”

Section: Introductionmentioning

confidence: 99%

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Dispersive Charge Transfer State Electroluminescence in Organic Solar Cells

Lampande

Pizano

Gui

et al. 2023

Advanced Energy Materials

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The notion of quasi-equilibrium is central to most solar cells; however, it has been questioned in organic photovoltaics (OPVs) owing to strong energetic disorder that frustrates efficient relaxation of electrons and holes within their respective density of states (DOS). Here, modulation electroluminescence (EL) spectroscopy is applied to OPVs and it is found that the frequency response of charge transfer (CT) state EL on the high energy side of the spectrum differs from that of the low energy side. This observation confirms that static disorder contributes substantially to the linewidth of the steady-state EL spectrum and is unambiguous proof that the distribution of CT states formed by electrical injection in the dark is not in quasi-equilibrium. These results emphasize the need for caution when analyzing OPV cells on the basis of reciprocity models that assume quasi-equilibrium holds, and highlight a new method to study this unusual aspect of OPV operation.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dispersive Charge Transfer State Electroluminescence in Organic Solar Cells

Lampande

Pizano

Gui

et al. 2023

Advanced Energy Materials

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“…The calculated average energy of this bound transitional state matches well with the binding energy of the weakly confined excitons in both the laser diodes. We emphasize that such occurrence of "negative activation energy" was not observed 37 in ordinary silicon diodes which do not show electroluminescence and perhaps are non-excitonic in nature.…”

Section: Discussionmentioning

confidence: 99%

“…Estimated f Max values initially decrease when forward bias (V dc ) slowly increases from zero. We must emphasize that observations of similar dynamic behavior of a small signal impedance response are also reproduced 37 in non-light emitting silicon diodes. We have mentioned that the defect response can be seen in capacitance measurements when modulation frequency (f) range matches with the transition rate (R).…”

Section: Experimental Results and Analysesmentioning

confidence: 99%

Negative activation energy and dielectric signatures of excitons and excitonic Mott transitions in quantum confined laser structures

Bhunia

Bansal

Henini

et al. 2016

Journal of Applied Physics

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Mostly, optical spectroscopies are used to investigate the physics of excitons, whereas their electrical evidences are hardly explored. Here, we examined a forward bias activated differential capacitance response of GaInP/AlGaInP based multi-quantum well laser diodes to trace the presence of excitons using electrical measurements. Occurrence of "negative activation energy" after light emission is understood as thermodynamical signature of steady state excitonic population under intermediate range of carrier injections. Similar corroborative results are also observed in an InGaAs/GaAs quantum dot laser structure grown by molecular beam epitaxy. With increasing biases, the measured differential capacitance response slowly vanishes. This represents gradual Mott transition of an excitonic phase into an electron-hole plasma in a GaInP/AlGaInP laser diode. This is further substantiated by more and more exponentially looking shapes of high energy tails in electroluminescence spectra with increasing forward bias, which originates from a growing non-degenerate population of free electrons and holes. Such an experimental correlation between electrical and optical properties of excitons can be used to advance the next generation excitonic devices. Published by AIP Publishing. [http://dx

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“…[14], [22] This happens due to the faster consumption of free charge carriers than their replenishment and the induced compensatory current, which lags behind the voltage and tries to establish equilibrium. [27] Mathematically, this is expressed as a positive-valued time derivative of the transient current response to a voltage step. [14], [28] Changes in the capacitance signal reveal changes in the carrier and the trap state density, leading to negative capacitance in QD devices.…”

mentioning

confidence: 99%

Revealing the Negative Capacitance Effect in Silicon Quantum Dot Light-Emitting Diodes via Temperature-Dependent Capacitance-Voltage Characterization

et al. 2022

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In this study, quantum dot light-emitting diodes based on non-toxic silicon quantum dots functionalized with hexyl and dodecyl organic ligands showed a negative capacitance effect. Current density-voltage (J −V ) measurements revealed the charge transport mechanisms in the QLEDs. The capacitancevoltage (C − V ) characteristics were measured with an LCR meter over a wide range of frequencies (200 Hz to 1 MHz) and at temperatures from −40 • C to 60 • C. The classical heterojunction theory can describe the operation of quantum LEDs, but an effect not predicted by Shockley's theory was observed. Negative capacitance values were recorded in both fabricated LEDs, which were not observed in SiQD-LEDs before. Hence, we investigate the negative capacitance origin and its influence on the device performance. We attribute the negative capacitance to trapmediated recombination, where charges at defect sub-bandgap states contribute to the recombination but cannot be replenished fast enough. As a result, a current flows to re-establish the equilibrium, which lags behind the applied voltage, and the NC appears. By comparing the two functionalizations, we also observed a different temperature dependence of the positive capacitance peak and a stronger negative capacitance effect for dodecyl functionalized SiQDs. This effect is attributed to their improved charge carrier confinement abilities.Index Terms-Silicon quantum dot (SiQD), light-emitting diode (LED), negative capacitance (NC). I. INTRODUCTIONQ ANTUM dot light-emitting diodes (QLEDs) are highly researched as promising electroluminescence (EL) devices. QDs itself combine the advantages of inorganic and organic materials by offering size-tunable emission, [1] high color purity, [2] easy processibility, [3] and high photoluminescence quantum efficiency. [4] Additionally, QLEDs are expected to have improved stability compared to OLEDs because of their inorganic crystalline materials. [5] Many conventional QDs consist of toxic or heavy metal materials, such as Cd or Pb, and therefore, alternative materials are researched. A promising alternative is nanosized silicon,

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Dynamics of electronic transitions and frequency dependence of negative capacitance in semiconductor diodes under high forward bias

Cited by 8 publications

References 16 publications

Dispersive Charge Transfer State Electroluminescence in Organic Solar Cells

Dispersive Charge Transfer State Electroluminescence in Organic Solar Cells

Negative activation energy and dielectric signatures of excitons and excitonic Mott transitions in quantum confined laser structures

Revealing the Negative Capacitance Effect in Silicon Quantum Dot Light-Emitting Diodes via Temperature-Dependent Capacitance-Voltage Characterization

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