Ultrafast Electron and Hole Dynamics in Germanium Nanowires

Prasankumar, R. P.; Choi, Sukgeun; Trugman, S. A.; Picraux, S. T.; Taylor, Antoinette J.

doi:10.1021/nl080202+

Cited by 56 publications

(85 citation statements)

References 39 publications

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“…It is not surprising as the previous reports on ultrafast pump-probe studies of Ge nanowires also showed the decrease in s 1 with decreasing nanowire diameter due to the carrier trapping at the nanowire surface. 50,54 The s 2 scarcely depends on the size and the surface of the structure but is mainly due to electron-hole pair recombination. The s 2 value is larger for porous nanowalls obtained on 30 Hz grown sample.…”

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confidence: 99%

Structural, optical and electronic properties of homoepitaxial GaN nanowalls grown on GaN template by laser molecular beam epitaxy

et al. 2015

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aWe have grown homoepitaxial GaN nanowall networks on GaN template using an ultra-high vacuum laser assisted molecular beam epitaxy system by ablating solid GaN target under a constant r.f. nitrogen plasma ambient. The effect of laser repetition rate in the range of 10 to 30 Hz on the structural properties of the GaN nanostructures has been studied using high resolution X-ray diffraction, field emission scanning electron microscopy and Raman spectroscopy. The variation of the laser repetition rate affected the tip width and pore size of the nanowall networks. The z-profile Raman spectroscopy measurements revealed the GaN nanowall network retained the same strain present in the GaN template. The optical properties of these GaN nanowall networks have been studied using photoluminescence and ultrafast spectroscopy and an enhancement of optical band gap has been observed for the nanowalls having a tip width of 10-15 nm due to the quantum carrier confinement effect at the wall edges. The electronic structure of the GaN nanowall networks has been studied using X-ray photoemission spectroscopy and it has been compared to the GaN template. The calculated Ga/N ratio is largest ($2) for the GaN nanowall network grown at 30 Hz. Surface band bending decreases for the nanowall network with the lowest tip width. The homoepitaxial growth of porous GaN nanowall networks holds promise for the design of nitride based sensor devices.

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confidence: 99%

Structural, optical and electronic properties of homoepitaxial GaN nanowalls grown on GaN template by laser molecular beam epitaxy

et al. 2015

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“…7−10 Although such sophisticated devices have been demonstrated, the investigation of the fundamental ultrafast carrier dynamics of semiconductor nanowire (NW) assemblies is so far limited to a small group of materials 11−13 and to qualitative analysis. 14,15 A quantitative translation of the photon response of NW assemblies to carrier dynamics in these structures is essential to exploit them in the design of nanoscale optoelectronic devices.…”

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confidence: 99%

“…This finding is generally consistent with several prior reports on surface recombination in semiconductor NWs. 13,14,16 Here we present the first quantitative analysis of a Ge NW−air metamaterial using the photon response of the assemblies to determine carrier dynamics. This analysis enables us to identify three time regimes for ultrafast recombination processes: Auger recombination (0−5 ps after photoexcitation), recombination via carrier trapping at fast surface states on the nanowires (5− 20 ps), and recombination via both fast and slow surface traps (20−200 ps).…”

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confidence: 99%

Ultrafast Carrier Dynamics of a Photo-Excited Germanium Nanowire–Air Metamaterial

Li¹,

Clady

Marshall³

et al. 2015

ACS Photonics

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Ultrafast carrier dynamics in arrays of single crystal and relatively uniform-diameter Ge nanowires (NWs) are investigated by transient absorption measurements and effective medium simulations. We present the first quantitative analysis of a Ge NW−air metamaterial, translating the photon response of the assemblies to carrier dynamics. Three time regimes of the ultrafast recombination process are identified: Auger recombination dominant (0−5 ps), "fast" surface trapping and recombination dominant (5−20 ps), and a mix of "fast" recombination and "slow" surface trapping (20−200 ps). The rates of surface recombination and their dependences on pump fluence are determined, highlighting the different interactions of electrons and holes with Ge NW surface and interface states. Structural and excitation conditions can be engineered to extend the photogenerated electron and hole lifetimes. Small wire diameters and low pump powers enhance the electron lifetime because charging of defect states in the surface oxide layer produces a potential barrier for electrons to be trapped at Ge/GeO x interface. This phenomenon simultaneously causes an enhancement of hole lifetime for relatively large wire diameters and large pump powers.

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“…The electron relaxation dynamics upon band-gap excitation in germanium have been investigated by several femtosecond pump-probe studies in the visible [1][2][3]. However, none of those studies addressed the fastest time scales of the excitation process itself or the carrier-carrier scattering dynamics in the first few fs after excitation.…”

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confidence: 99%