Electron transport in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">TiO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>probed by THz time-domain spectroscopy

Hendry, Euan; Wang, Feng; Shan, Jie; Heinz, Tony F.; Bonn, Mischa

doi:10.1103/physrevb.69.081101

Cited by 220 publications

(145 citation statements)

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“…10. We extend previous THz-TDS conductivity measurements on doped 11 and photoexcited semiconductors 9,12 to study electron-hole plasmas in highly photoexcited semiconductors. We determine in the time domain the electric field of picosecond THz pulses transmitted through the unexcited sample E͑t͒, and the change on photoexcitation ⌬E͑t͒, as shown in Fig.…”

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confidence: 82%

“…21͒ and TiO 2 . 9 For TiO 2 , the deviation from linearity for f l Ͼ 1 J/m 2 suggests that the effective mass in this material is density dependent: these deviations occur for N av Ͼ 1 ϫ 10 25 m −3 ͑ p Ͼ 70 THz͒, 19 similar to zinc oxide. 22 For Si, band calculations 3 indicate that the electron effective mass is constant over the density range investigated here, partly due to the sixfold degenerate band structure in Si.…”

Section: Using 17mentioning

confidence: 99%

“…Indeed, for TiO 2 , electron-phonon interactions have been shown to suffice to account for the temperature-dependent scattering rate down to 10 K. 9 For Si, it has been shown that impurity scattering rates drop below phonon scattering rates as doping levels are decreased, also at 30 K. 23 We therefore analyze our data as a sum of contributions from charge-phonon scattering ͑1/ ph ͒ and charge-charge scattering ͑1/ eh ͒. Both rates are affected at high carrier concentrations: to a first approximation, 1 / eh will increase proportionally to the charge concentration N, while, due to band filling, 1 / ph will scale as N 1 3 .…”

Section: Using 17mentioning

confidence: 99%

“…The samples are cooled to 30 K in a helium cryostat to minimize effects of electron-optical phonon scattering that prevail at higher temperatures in TiO 2 . 9 The THz-TDS setup is similar to that described in Ref. 10.…”

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Reduction of carrier mobility in semiconductors caused by charge-charge interactions

et al. 2007

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We investigate the effect of charge-charge interactions on carrier mobility in titanium dioxide ͑TiO 2 ͒ and silicon ͑Si͒ using terahertz spectroscopy. Charge scattering times and plasma frequencies are directly determined as a function of charge density. In Si, a linear increase in scattering rate for densities exceeding 10 21 m −3 is attributed to electron-hole scattering. In contrast, in TiO 2 , charge-charge interactions are suppressed due to dielectric screening, highlighting the vastly different dielectric properties for these two materials. DOI: 10.1103/PhysRevB.75.233202 PACS number͑s͒: 72.40.ϩw, 72.10.Di, 72.20.Dp Charge-charge interactions determine many of the properties of highly doped or photoexcited semiconductors. Carrier-carrier collisions, for instance, can strongly affect the conductivity, and the decrease of electron and hole drift mobilities with increasing charge carrier densities is an important factor in determining the current-voltage characteristics of, for example, semiconductor diodes at increased current densities 1 and solar cells under strong illumination conditions. 2 Charge mobility depends on two quantities: its effective mass and scattering time ͑i.e., the average time in-between momentum-randomizing events, due to, e.g., electronphonon scattering͒. Theory has indicated that both of these quantities can be strongly dependent on the free charge density in semiconductors. [3][4][5] Experimental investigations of carrier-carrier interactions are, however, intrinsically more complex, as most experimental techniques ͑such as optical reflectivity measurements 6,7 ͒ cannot easily distinguish between changes in scattering time and effective mass. Terahertz time-domain spectroscopy ͑THz-TDS͒, with its ability to determine both the real and imaginary components of the complex conductivity, 8 allows us to differentiate between density-dependent changes in effective mass from changes in scattering time.Here, we compare the high-density photoconductivity of single crystal silicon ͑Si͒ and rutile-type titanium dioxide ͑TiO 2 ͒, two technologically relevant materials with low and high dielectric functions, respectively. By photoexciting with intense, femtosecond ultraviolet laser pulses and probing with THz pulses, we can generate and measure high-density plasmas in semiconductors on ultrafast time scales, accessing plasma densities spanning 5 orders of magnitude from 10 21 to 10 26 m −3 . In Si, we find that the scattering rate increases linearly for densities Ͼ10 21 m −3 , an effect characteristic of direct charge-charge scattering. For TiO 2 , the variation of the scattering rate with density is much weaker and is caused by band filling effects. The difference between these two materials is shown to originate from their vastly different dielectric screening properties.The TiO 2 ͑1 mm thick 001 rutile crystal grown commercially by the Verneuil method by Crystal-GmbH͒ and silicon ͑0.5 mm thick undoped Si wafer, grown by the Czochralski method with estimated impurity density Ͻ10 13 cm −3 ,...

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confidence: 82%

Section: Using 17mentioning

confidence: 99%

Section: Using 17mentioning

confidence: 99%

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confidence: 99%

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Reduction of carrier mobility in semiconductors caused by charge-charge interactions

et al. 2007

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“…So far, the charge carrier dynamics in TiO 2 has intensely been studied by ultrafast broadband transient absorption (TA) spectroscopy from the terahertz to the visible [27][28][29][30][31][32][33][34][35]. In these studies, the photoexcited electrons and holes in the system were treated as uncorrelated, an approximation that is valid only when the pump photons are non-resonant with the excitons [21].…”

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Clocking the Ultrafast Electron Cooling in Anatase Titanium Dioxide Nanoparticles

et al. 2018

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The recent identification of strongly bound excitons in room temperature anatase TiO 2 single crystals and nanoparticles underscores the importance of bulk many-body effects in samples used for applications. Here, for the first time, we unravel the interplay between many-body interactions and correlations in highly-excited anatase TiO 2 nanoparticles using ultrafast two-dimensional deepultraviolet spectroscopy. With this approach, under non-resonant excitation, we disentangle the optical nonlinearities contributing to the bleach of the lowest direct exciton peak. This allows us to clock the ultrafast timescale of the hot electron thermalization in the conduction band with unprecedented temporal resolution, which we determine to be < 50 fs, due to the strong electronphonon coupling in the material. Our findings call for the design of alternative resonant excitation schemes in photonics and nanotechnology.1 arXiv:1703.07818v2 [cond-mat.mes-hall] 13 Jan 2018In the last decades, anatase TiO 2 has attracted huge interest as one of the most promising materials for a variety of challenging applications, ranging from photocatalysis [1,2] and photovoltaics [3] to sensors [4,5]. Since these technologies involve charge transport, thermalization and localization, they call for studies of the fast electron and hole dynamics, which provide a deep knowledge of the nature of the photogenerated/injected charge carriers and of the energy balance therein. These processes intimately depend on the details of the electronic structure and the presence of many body-effects in the material. Since anatase TiO 2 is a d 0 transition metal oxide, strong electron-electron correlations do not play a substantial role in the electronic structure [6]. Hence, this solid can be classified within the simple band insulator scheme, in which the forbidden energy gap arises as a result of band theory and is not a consequence of the strong on-site Coulomb interaction. However, different to conventional band insulators, anatase TiO 2 represents a peculiar example in which electron-phonon interaction and electron-hole correlation become relatively strong and influence the optical spectra. On the one hand, the presence of a moderately large electron-phonon coupling in anatase TiO 2 has often been invoked to interpret experimental results naturally pointing to the polaronic (self-trapped) picture [7][8][9][10][11][12][13]. Notable examples include the low temperature green photoluminescence (PL) due to self-trapped excitons [14][15][16][17][18][19][20] and the room temperature electron mobilities whose values are limited by strong scattering with phonons [10]. On the other hand, many-body correlations have been thought to be negligible in this material and, as such, they remained widely unexplored. Recently, by employing state-of-the-art experimental [21] and computational techniques [21][22][23][24][25], the substantial role of electron-hole Coulomb correlations was unravelled in the anatase polymorph of TiO 2 . Strongly bound direct excitons were...

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Self‐Cleaning Materials for Plastic and Plastic‐Containing Substrates

Yaghoubi¹

2013

Self‐Cleaning Materials and Surfaces

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Electron transport inTiO2probed by THz time-domain spectroscopy

Cited by 220 publications

References 26 publications

Reduction of carrier mobility in semiconductors caused by charge-charge interactions

Reduction of carrier mobility in semiconductors caused by charge-charge interactions

Clocking the Ultrafast Electron Cooling in Anatase Titanium Dioxide Nanoparticles

Self‐Cleaning Materials for Plastic and Plastic‐Containing Substrates

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