Determination of hydrogenated amorphous silicon electronic transport parameters and density of states using several photoconductivity techniques

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

doi:10.1063/1.4737790

Cited by 10 publications

(19 citation statements)

References 17 publications

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“…Ventosinos et al 11 deduced a simpler version of Eq. (1) for the first time, while Longeaud et al 14 proposed the actual Eq. (1) as a way of gaining precision.…”

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%

“…It is important to mention that the new pairs of formulas presented above, as well as the formula presented by Longeaud et al, 14 have to be used recursively, since the band tails' characteristic temperatures and the DOS at the band edges are present in the expressions. So, it is necessary to have an initial estimate of these two parameters, which are then refined by the recursive application of the formulas.…”

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

“…The last equalities in Eqs. (14) and (16) are strictly valid only for T < T C , but they are actually good approximations of the first integral for temperatures T 0.75T C . Replacing Eqs.…”

Section: B Deduction Of the Formulasmentioning

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%

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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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“…Ventosinos et al 11 deduced a simpler version of Eq. (1) for the first time, while Longeaud et al 14 proposed the actual Eq. (1) as a way of gaining precision.…”

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

Section: A New Equations For Band Tail Spectroscopymentioning

confidence: 99%

“…The last equalities in Eqs. (14) and (16) are strictly valid only for T < T C , but they are actually good approximations of the first integral for temperatures T 0.75T C . Replacing Eqs.…”

Section: B Deduction Of the Formulasmentioning

confidence: 99%

Section: -6mentioning

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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Photoconductivity in Materials Research

Reynolds

Brinza

Benkhedir

et al. 2017

Springer Handbook of Electronic and Photonic Materials

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Electrical transport through materials is a large and complex field, and in this chapter we cover only a few aspects that are relevant to practical applications. We start with a review of the semi-classical approach that leads to the concepts of drift velocity, mobility and conductivity, from which Matthiessen's Rule is derived. A more general approach based on the Boltzmann transport equation is also discussed. We review the conductivity of metals and include a useful collection of experimental data. The conductivity of nonuniform materials such as alloys, polycrystalline materials, composites and thin films is discussed in the context of Nordheim's rule for alloys, effective medium theories for inhomogeneous materials, and theories of scattering for thin films. We also discuss some interesting aspects of conduction in the presence of a magnetic field (the Hall effect). We present a simplified analysis of charge transport in semiconductors in a high electric field, including a modern avalanche theory (the theory of lucky drift). The properties of low-dimensional systems are briefly reviewed, including the quantum Hall effect.

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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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Determination of hydrogenated amorphous silicon electronic transport parameters and density of states using several photoconductivity techniques

Cited by 10 publications

References 17 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

Photoconductivity in Materials Research

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

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