Density of states evaluations from oscillating/moving grating techniques

Ventosinos, Federico; Longeaud, Christophe; Schmidt, Javier Alejandro

doi:10.1016/j.jnoncrysol.2011.12.046

Cited by 6 publications

(23 citation statements)

References 10 publications

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“…In turn, s 0 can be obtained from the photoconductivity-based techniques MGT/OPG. 12 To calculate E tn , the steady-state photoconductivity r measured under an illumination that produces a uniform generation of carriers within the material, should be used in the following formula:…”

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

“…To obtain s 0 from OPG/MGT, it is necessary that the conditions of the experiment situate the sample in the lifetime regime for a sufficiently large range of illuminations and/or temperatures, [11][12][13][14] which cannot be achieved for certain a-Si:H samples. In that case, it is difficult to get s 0 from OPG/MGT with good precision, and thus Eqs.…”

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

“…1 of Ref. 12. A laser light, linearly polarized in the vertical direction, is split into two coherent beams that finally interfere on the position of the sample.…”

Section: -6mentioning

confidence: 99%

“…A plot of this current as a function of Df results in a well-defined peak for a certain frequency, which can be used to obtain the small-signal recombination lifetime s 0 . 12,14 At the IFIS-Litoral Laboratory (Santa Fe, Argentina), we have measured s 0 for the same temperatures and in the same range of generation rates used for the SSPC and SSPG experiments, obtaining values between 2 Â 10 À5 and 10 À4 s. Therefore, we have most of the parameters needed to apply Eqs. (4), (5), 7, and (8); except for the capture coefficients, the mobilities, and the values of the DOS at the band edges.…”

Section: -6mentioning

confidence: 99%

“…In recent publications, we have proposed a simple and a more sophisticated formula for assessing the DOS in the conduction band tail (CBT) from measurements of OPG/MGT. 12,13 For a semiconductor under a spatially and temporally uniform generation rate G (steady state conditions), the total concentration of electrons n T should be equal to the total concentration of holes p T , as can be proved from Maxwell's first equation. Consequently, the partial derivatives with respect to the generation rate should also be equal: s n 0 ¼ @n T / @G should be equal to the corresponding time for holes, s p 0 ¼ @p T /@G. Therefore, this common small-signal recombination lifetime s 0 should provide information not only about the CBT but also about the valence band tail (VBT).…”

Section: Introductionmentioning

confidence: 99%

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Obtainment of the density of states in the band tails of hydrogenated amorphous silicon

Kopprio

Longeaud

Schmidt

2017

Journal of Applied Physics

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In this work, we present two new pairs of formulas to obtain a spectroscopy of the density of states (DOS) in each band tail of hydrogenated amorphous silicon (a-Si:H) from photoconductivity-based measurements. The formulas are based on the knowledge of the small-signal recombination lifetime s 0 , the characteristic decay time of the concentration of trapped carriers generated in excess by the illumination, and that can be measured by methods like the Oscillating Photocarrier Grating (OPG) or Moving Grating Technique (MGT). First, we deduce the formulas and test their accuracy by numerical simulations using typical a-Si:H parameters. Next, we characterize an a-Si:H sample using well-known methods, like Fourier transform photocurrent spectroscopy to evaluate the valence band tail and modulated photoconductivity to measure the conduction band tail. We also performed measurements of steady-state photoconductivity, steady-state photocurrent grating and MGT, for a range of generation rates. From these measurements-and taking typical values for the capture coefficients, the extended states mobilities and the DOS at the band edges-we apply the new formulas to get the band tails. We find that the results obtained from the application of our formulas are in good agreement with those found with the traditional methods for both band tails. Moreover, we show that MGT/OPG measurement to get s 0 can be avoided if one of the band tails is measured by one of the traditional methods, since the known band tail can be used to evaluate s 0 with one pair of equations, and then the other pair can be applied to get the other band tail. Published by AIP Publishing.

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Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

“…1 of Ref. 12. A laser light, linearly polarized in the vertical direction, is split into two coherent beams that finally interfere on the position of the sample.…”

Section: -6mentioning

confidence: 99%

Section: -6mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Obtainment of the density of states in the band tails of hydrogenated amorphous silicon

Kopprio

Longeaud

Schmidt

2017

Journal of Applied Physics

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Further insight into the oscillating photocarrier grating technique: influence of the oscillation amplitude

et al. 2021

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Allowing for the simultaneous determination of the photocarriers drift mobilities and their smallsignal recombination lifetime, the Moving photocarrier Grating Technique (MGT) is a useful characterization tool for photoconductive semiconductors. This technique is based on measuring the steady-state direct current induced by an interference pattern (IP) moving at a constant velocity between two coplanar ohmic contacts deposited on the semiconductor. The main drawback of the technique is the low level of the signal to be measured, which can be masked by noise. The Oscillating Photocarrier Grating technique (OPG), where the IP oscillates at constant speed, has been proposed as an alternating current version of MGT, providing a higher signal-to-noise ratio. The IP oscillation is produced by the phase modulation of one of the interfering beams. Using the multiple trapping model we deduce the expression of the current density generated by OPG in a photoconductor. We observed theoretically and experimentally that OPG is not equivalent to MGT for the previously used amplitude of oscillation, especially when the IP moves at high speeds. However, we show that the desired equivalence between both techniques could be recovered by increasing the amplitude of oscillation. A phase modulator capable of achieving such amplitudes is required for the correct implementation of OPG.

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Subgap density of states spectroscopy using steady-state photoconductivity-based experiments

Kopprio

Longeaud

Schmidt

2023

Journal of Non-Crystalline Solids

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Density of states evaluations from oscillating/moving grating techniques

Cited by 6 publications

References 10 publications

Obtainment of the density of states in the band tails of hydrogenated amorphous silicon

Obtainment of the density of states in the band tails of hydrogenated amorphous silicon

Further insight into the oscillating photocarrier grating technique: influence of the oscillation amplitude

Subgap density of states spectroscopy using steady-state photoconductivity-based experiments

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