Electron-hole recombination on ZnO(0001) single-crystal surface studied by time-resolved soft X-ray photoelectron spectroscopy

Yukawa, Ryu; Ozawa, K.; Emori, Masato; Ogawa, M.; Yamamoto, Shûji; Fujikawa, K.; Hobara, Rei; Kitagawa, S.; Daimon, Hiroshi; Sakama, Hiroshi; Matsuda, Iwao

doi:10.1063/1.4897934

Cited by 36 publications

(20 citation statements)

References 30 publications

(61 reference statements)

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“…A detailed analysis of the time traces around zero delay results in an upper limit of 10 fs for the electron lifetime in the UHB (Supplementary Note 1). We emphasize that the observed electron lifetime at the bottom of the (undoped) UHB is three orders-of-magnitude shorter than the value expected at the conduction band minimum of conventional semiconductors with a similar band gap [18][19][20] .…”

Section: Resultsmentioning

confidence: 63%

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

et al. 2020

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Charge excitations across an electronic band gap play an important role in opto-electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund’s physics in strongly correlated photoexcited NiO. By combining time-resolved two-photon photoemission experiments with state-of-the-art numerical calculations, an ultrafast (≲10 fs) relaxation due to Hund excitations and related photo-induced in-gap states are identified. Remarkably, the weight of these in-gap states displays long-lived coherent THz oscillations up to 2 ps at low temperature. The frequency of these oscillations corresponds to the strength of the antiferromagnetic superexchange interaction in NiO and their lifetime vanishes slightly above the Néel temperature. Numerical simulations of a two-band t-J model reveal that the THz oscillations originate from the interplay between local many-body excitations and antiferromagnetic spin correlations.

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Section: Resultsmentioning

confidence: 63%

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

et al. 2020

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“…It is well known that the recombination time for photo-induced charge carriers in indirect band semiconductors as TiO 2 , is very long [25], this being one of the causes of the very good photocatalytic activity of this material. However, the recombination time of charge carriers in a direct gap semiconductor as ZnO is much shorter, but it increases exponentially with the energy band bending at grain interfaces [26]. On the other hand, ZnN has been identified as an indirect band-gap semiconductor [27], so that an increase in the recombination time of charge carriers with the increase of nitrogen content in ZnO x N y thin films is expected.…”

Section: Photo-current Characterizationmentioning

confidence: 99%

High visible light photocatalytic activity of nitrogen-doped ZnO thin films deposited by HiPIMS

Tiron

Velicu

Stanescu

et al. 2017

Surface and Coatings Technology

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International audienceReactive High Power Impulse Magnetron Sputtering (HiPIMS) of a pure Zn target in Ar/N$_2$/O$_2$ gas mixture was used to synthesize ZnO$_x$N$_y$ thin films with nitrogen content and optical band-gap energy values ranging over 0–6.2 at.% and 3.34–1.67 eV, respectively. The fine control of the nitrogen content in the deposited ZnO$_x$N$_y$ thin films composition was possible through the stabilization of the reactive HiPIMS discharge in the transition region, between the metallic and compound target sputtering modes. Various analytical techniques such as AFM, XPS, XRD, UV–Vis and Raman spectroscopy have been employed to characterize the properties of the deposited thin films. The photocatalytic activity, light excitation efficiency and life time of photo-generated charge carriers in the ZnO$_x$N$_y$ films were investigated by photo-electrochemical and photo-current measurements during visible light on/off irradiation cycles. The as-deposited films showed poor visible-light photocatalytic activity and photo-current response. Post-deposition annealing of the films in nitrogen atmosphere resulted in a slight enhancement of crystalline order. However, the thermal treatment improved considerably the film photocatalytic activity and stability for water splitting under visible light irradiation. The optimum photo-current response and photocata-lytic activity have been obtained for the annealed ZnO$_x$N$_y$ films with a nitrogen content of 3.4 at.% (photon-to-current efficiency up to 33% at λ = 370 nm and 0.5 V biasing potential vs. Ag/AgCl). Increasing the nitrogen content above this value, in spite of lowering the energy band-gap, worsened the visible light photocatalytic activity of the films due to deterioration of the crystalline order

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“…We expected the HfO 2 /n-ZnO/p-Si or ‘hole source' MOSCAP to operate primarily at inversion, because the p-Si would inject its majority hole carriers into n-ZnO. Also critical to this function, the n-ZnO film thickness was designed to be significantly lesser than its hole diffusion length 15 . A HfO 2 /n-ZnO control (null hypothesis) or ‘no holes source' MOSCAP was also fabricated consisting of just HfO 2 /n-ZnO grown on sapphire for comparison ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Sustained hole inversion layer in a wide-bandgap metal-oxide semiconductor with enhanced tunnel current

et al. 2016

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Wide-bandgap, metal-oxide thin-film transistors have been limited to low-power, n-type electronic applications because of the unipolar nature of these devices. Variations from the n-type field-effect transistor architecture have not been widely investigated as a result of the lack of available p-type wide-bandgap inorganic semiconductors. Here, we present a wide-bandgap metal-oxide n-type semiconductor that is able to sustain a strong p-type inversion layer using a high-dielectric-constant barrier dielectric when sourced with a heterogeneous p-type material. A demonstration of the utility of the inversion layer was also investigated and utilized as the controlling element in a unique tunnelling junction transistor. The resulting electrical performance of this prototype device exhibited among the highest reported current, power and transconductance densities. Further utilization of the p-type inversion layer is critical to unlocking the previously unexplored capability of metal-oxide thin-film transistors, such applications with next-generation display switches, sensors, radio frequency circuits and power converters.

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Electron-hole recombination on ZnO(0001) single-crystal surface studied by time-resolved soft X-ray photoelectron spectroscopy

Cited by 36 publications

References 30 publications

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

High visible light photocatalytic activity of nitrogen-doped ZnO thin films deposited by HiPIMS

Sustained hole inversion layer in a wide-bandgap metal-oxide semiconductor with enhanced tunnel current

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