Imaging ambipolar diffusion of photocarriers in GaAs thin films

Paget, D.; Cadiz, Fabian; Rowe, A. C. H.; Moreau, F.; Arscott, S.; Peytavit, E.

doi:10.1063/1.4730396

Cited by 26 publications

(31 citation statements)

References 16 publications

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“…Equation (B2) is approximate since, as justified in Ref [18], it assumes charge neutrality [n = δp]. Further, it neglects for simplicity the spatial dependences of electron and hole conductivities.…”

Section: Discussionmentioning

confidence: 99%

“…Here, we present a theoretical and experimental investigation of the effect of degeneracy on spin transport in p + GaAs using a polarized microluminescence method in which the spin polarization is measured as a function of distance from a local, diffraction-limited excitation spot [17][18][19]. This study reveals that the dominant effect of degeneracy is the spin dependence of diffusion.…”

Section: Introductionmentioning

confidence: 99%

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Effect of the Pauli principle on photoelectron spin transport inp+GaAs

et al. 2015

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In p + GaAs thin films, the effect of photoelectron degeneracy on spin transport is investigated theoretically and experimentally by imaging the spin polarization profile as a function of distance from a tightly-focussed light excitation spot. Under degeneracy of the electron gas (high concentration, low temperature), a dip at the center of the polarization profile appears with a polarization maximum at a distance of about 2 µm from the center. This counterintuitive result reveals that photoelectron diffusion depends on spin, as a direct consequence of the Pauli principle. This causes a concentration dependence of the spin stiffness while the spin dependence of the mobility is found to be weak in doped material. The various effects which can modify spin transport in a degenerate electron gas under local laser excitation are considered. A comparison of the data with a numerical solution of the coupled diffusion equations reveals that ambipolar coupling with holes increases the steady-state photo-electron density at the excitation spot and therefore the amplitude of the degeneracy-induced polarization dip. Thermoelectric currrents are predicted to depend on spin under degeneracy (spin Soret currents), but these currents are negligible except at very high excitation power where they play a relatively small role. Coulomb spin drag and bandgap renormalization are negligible due to electrostatic screening by the hole gas.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of the Pauli principle on photoelectron spin transport inp+GaAs

et al. 2015

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“…[8][9][10][11][12][13][14] However, the density of photoexcited carriers can strongly influence the measured diffusion coefficients. 8,13,14 Experiments on n-type semiconductors give a consistent result: D a is either an increasing or a flat function of photocarrier density. For instance, recent work on n-GaAs quantum wells has shown D a (or the related "ambipolar spin diffusion") to be increasing in lightly doped wells 15 and flat in nominally undoped wells.…”

Section: Introductionmentioning

confidence: 99%

Diffusion of degenerate minority carriers in a p-type semiconductor

Weber

Kittlaus

2013

Journal of Applied Physics

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We report ultrafast transient-grating experiments on heavily p-type InP at 15 K. Our measurement reveals the dynamics and diffusion of photoexcited electrons and holes as a function of their density n in the range 2 × 10 16 to 6 × 10 17 cm −3 . After the first few picoseconds the grating decays primarily due to ambipolar diffusion. While at low density we observe a regime in which the ambipolar diffusion is electron-dominated and increases rapidly with n, at high n it appears to saturate at 34 cm 2 /s. We present a simple calculation that reproduces the main results of our measurements as well as of previously published measurements that had shown diffusion to be a flat or decreasing function of n. By accounting for effect of density on charge susceptibility we show that, in p-type semiconductors, the regime we observe of increasing ambipolar diffusion is unique to heavy doping and low temperature, where both the holes and electrons are degenerate; in this regime the electronic and ambipolar diffusion are nearly equal. The saturation is identified as a crossover to ambipolar diffusion dominated by the majority carriers, the holes. At short times the transient-grating signal rises gradually. This rise reveals cooling of hot electrons and, at high photocarrier density, allows us to measure ambipolar diffusion of 110 cm 2 /s in the hot-carrier regime.

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“…4. The carrier diffusion length in the sample over this time window is ∼140 nm [29]. This is much shorter than the characteristic length scale in the experiment, i.e.…”

Section: Thz Diffraction Measurementsmentioning

confidence: 94%

Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films

Steinbusch¹,

Tyagi²,

Schaafsma³

et al. 2014

Opt. Express

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Abstract:We demonstrate active beam steering of terahertz radiation using a photo-excited thin layer of gallium arsenide. A constant gradient of phase discontinuity along the interface is introduced by an spatially inhomogeneous density of free charge carriers that are photo-generated in the GaAs with an optical pump. The optical pump has been spatially modulated to form the shape of a planar blazed grating. The phase gradient leads to an asymmetry between the +1 and -1 transmission diffracted orders of more than a factor two. Optimization of the grating structure can lead to an asymmetry of more than one order of magnitude. Similar to metasurfaces made of plasmonic antennas, the photo-generated grating is a planar structure that can achieve large beam steering efficiency. Moreover, the photo-generation of such structures provides a platform for active THz beam steering.

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Imaging ambipolar diffusion of photocarriers in GaAs thin films

Cited by 26 publications

References 16 publications

Effect of the Pauli principle on photoelectron spin transport inp+GaAs

Effect of the Pauli principle on photoelectron spin transport inp+GaAs

Diffusion of degenerate minority carriers in a p-type semiconductor

Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films

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