Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs

Lloyd‐Hughes, James; Merchant, S.K.E.; Feng, Lan; Tan, Hark Hoe; Jagadish, Chennupati; Castro-Camus, E.; Johnston, Michael B.

doi:10.1063/1.2398915

Cited by 103 publications

(77 citation statements)

References 21 publications

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“…The surface recombination velocity, S, which is 1000 cm/ s in InP, 3,4 is three orders of magnitude larger ͑10 6 cm/ s͒ for GaAs. 5,6 Recent time-resolved pump-probe terahertz spectroscopy showed that the carrier lifetime in bare GaAs wires is approximately 1 ps, consistent with the expected nonradiative lifetime of NR Ϸ d / 2S Ϸ 1.5 ps for a NW diameter of 30 nm and S =10 6 cm/ s. 7 In addition, the low temperature hole mobility in GaAs is an order of magnitude larger than for InP, which results in a diffusion length which is three times larger than for InP; this increases the sensitivity of carriers to defects within the bulk of the NW core. The recombination lifetime in GaAs is also particularly sensitive to bulk defects such as vacancies and arsenic-antisite defects.…”

Section: Nearly Intrinsic Exciton Lifetimes In Single Twin-free Gaas/mentioning

confidence: 99%

Nearly intrinsic exciton lifetimes in single twin-free GaAs∕AlGaAs core-shell nanowire heterostructures

Perera

Fickenscher

Jackson

et al. 2008

Applied Physics Letters

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130

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CW and time-resolved photoluminescence measurements are used to investigate exciton recombination dynamics in GaAs∕AlGaAs heterostructure nanowires grown with a recently developed technique which minimizes twinning. A thin capping layer is deposited to eliminate the possibility of oxidation of the AlGaAs shell as a source of oxygen defects in the GaAs core. We observe exciton lifetimes of ∼1ns, comparable to high quality two-dimensional double heterostructures. These GaAs nanowires allow one to observe state filling and many-body effects resulting from the increased carrier densities accessible with pulsed laser excitation.

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Section: Nearly Intrinsic Exciton Lifetimes In Single Twin-free Gaas/mentioning

confidence: 99%

Nearly intrinsic exciton lifetimes in single twin-free GaAs∕AlGaAs core-shell nanowire heterostructures

Perera

Fickenscher

Jackson

et al. 2008

Applied Physics Letters

Self Cite

114

130

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“…However, it was found that surface-passivated (SP) GaAs PCS emitters tend to show a degraded performance over time, which was attributed to the oxidation of the treated surfaces under continued exposure to air [4].…”

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confidence: 99%

Improved Performance of GaAs-Based Terahertz Emitters via Surface Passivation and Silicon Nitride Encapsulation

Headley

Parkinson

et al. 2011

IEEE J. Select. Topics Quantum Electron.

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Abstract-We have improved the stability and performance of terahertz (THz) photoconductive (Auston) switches using a combination of (NH 4 ) 2 S surface passivation (SP) and silicon nitride (Si 3 N 4 ) encapsulation. The influences of SP and encapsulation on the ultrafast electron dynamics in GaAs were examined using THz emission spectroscopy and optical pump-THz probe spectroscopy. The power of THz radiation from the surface of photoexcited GaAs increased by a factor of 5 after passivation and encapsulation, while the process lengthened the trapping time for photoexcited charge carriers. By fabricating and assessing the performance of photoconductive switches, we found that passivation and encapsulation increased the average THz power generated fourfold.

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“…3,12 Control of the surface chemistry is therefore essential in order for these objects to be implemented successfully in nanoscale devices. Chemical surface passivation of GaAs surfaces has previously been shown to reduce both the surface trap density 13 and potentially also the surface recombination velocity. 14 The latter has been attributed to a change in surface potential, and a subsequent reduction in the thickness of the surface depletion region.…”

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confidence: 99%

Carrier Lifetime and Mobility Enhancement in Nearly Defect-Free Core−Shell Nanowires Measured Using Time-Resolved Terahertz Spectroscopy

et al. 2009

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We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.Semiconductor nanowires are promising new materials for implementation in nanoscale electronic and optoelectronic devices. Of particular interest are III-V semiconductor nanowires, which can exhibit a direct bandgap and a high electron mobility.1 However, the large surface-to-volume ratio inherent to nanowires results in the presence of surface traps offering easy access to carrier and exciton recombination pathways.2,3 In addition, one-temperature growth techniques have been shown to cause a significant twin-defect (stacking-defect) density within the nanowires. 4 Refinements in the epitaxial growth of these nanowires are therefore essential in order for their optoelectronic and crystallographic standards to approach those of bulk material.2,6,7 Such efforts are complicated by the fact that electrical measurements conducted on nanowires to determine charge-carrier mobility are often obscured by properties of the electrical contacts. Most contactless spectroscopic probes of nanowires to date have relied upon low-temperature photoluminescence measurements to characterize optoelectronic quality by measuring excitonic dynamics and radiative quantum efficiency. 2,6However, for use of these materials in nanoelectronics and optoelectronics, it is essential to determine charge-carrier mobility and lifetime at room temperature.In this study, we have conducted transient photoconductivity measurements on an ensemble of nanowires in order to assess the effect of nearly defect-free (two-temperature) growth and core-shell encapsulation technologies on charge-carrier trapping and mobility. Optical-pump terahertz-probe spectroscopy was employed as a noncontact ultrafast probe of the room-temperature photoconductivity with subpicosecond resolution. We demonstrate that both two-temperature growth and encapsulation of the GaAs nanowires with a higher band gap material lead to significant increases in the lifetime of free charge carriers. Encapsulation of the nanowires is shown to be highly effective, reducing the areal density of surface traps to one-seventh of that for the untreated wires. Importantly, we find that moving from one-temperature growth to a two-temperature procedure (comprising a brief high-temperature step for nucleation and a longer lower-temperature phase for prolonged growth 4 ) increases the intrinsic carrier mobility of the wires from 1200 cm 2 /(V s) to 2250 cm 2 /(V s).All nanowire samples were initially grown onto a GaAs substrate as shown in a representative scanning electron microscopy ...

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Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs

Cited by 103 publications

References 21 publications

Nearly intrinsic exciton lifetimes in single twin-free GaAs∕AlGaAs core-shell nanowire heterostructures

Nearly intrinsic exciton lifetimes in single twin-free GaAs∕AlGaAs core-shell nanowire heterostructures

Improved Performance of GaAs-Based Terahertz Emitters via Surface Passivation and Silicon Nitride Encapsulation

Carrier Lifetime and Mobility Enhancement in Nearly Defect-Free Core−Shell Nanowires Measured Using Time-Resolved Terahertz Spectroscopy

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