title: Modulation doping of GaAs/AlGaAs core-shell nanowires with effective defect passivation and high electron mobility.
abstract: Reliable doping is required to realize many devices based on semiconductor nanowires. Group III-V nanowires show great promise as elements of high-speed optoelectronic devices, but for such applications it is important that the electron mobility is not compromised by the inclusion of dopants. Here we show that GaAs nanowires can be n-type doped with negligible loss of electron mobility. Molecular beam epitaxy was used to fabricate modulation-doped GaAs nanowires with Al0.33Ga0.67As shells that contained a layer of Si dopants. We identify the presence of the doped layer from a high-angle annular dark field scanning electron microscopy cross-section image. The doping density, carrier mobility, and charge carrier lifetimes of these n-type nanowires and nominally undoped reference samples were determined using the noncontact method of optical pump terahertz probe spectroscopy. An n-type extrinsic carrier concentration of 1.10 ± 0.06 × 10(16) cm(-3) was extracted, demonstrating the effectiveness of modulation doping in GaAs nanowires. The room-temperature electron mobility was also found to be high at 2200 ± 300 cm(2) V(-1) s(-1) and importantly minimal degradation was observed compared with undoped reference nanowires at similar electron densities. In addition, modulation doping significantly enhanced the room-temperature photoconductivity and photoluminescence lifetimes to 3.9 ± 0.3 and 2.4 ± 0.1 ns respectively, revealing that modulation doping can passivate interfacial trap states.
authors.affiliation: Department of Physics, University of Oxford , Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Boland
authors.forename: Sonia
authors.initials: S
authors.lastname: Conesa-Boj
authors.forename: Patrick
authors.initials: P
authors.lastname: Parkinson
authors.forename: Gözde
authors.initials: G
authors.lastname: Tütüncüoglu
authors.forename: Federico
authors.initials: F
authors.lastname: Matteini
authors.forename: Daniel
authors.initials: D
authors.lastname: Rüffer
authors.forename: Alberto
authors.initials: A
authors.lastname: Casadei
authors.forename: Francesca
authors.initials: F
authors.lastname: Amaduzzi
authors.forename: Fauzia
authors.initials: F
authors.lastname: Jabeen
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Davies
authors.forename: Hannah J
authors.initials: HJ
authors.lastname: Joyce
authors.forename: Laura M
authors.initials: LM
authors.lastname: Herz
authors.forename: Anna
authors.initials: A
authors.lastname: Fontcuberta i Morral
authors.forename: Michael B
authors.initials: MB
authors.lastname: Johnston
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D001152:Arsenicals / Q000737:chemistry*; D004583:Electrons; D005708:Gallium / Q000737:chemistry*; D017348:Microscopy, Electron, Scanning Transmission; D053770:Nanowires
chemical_list: D001152:Arsenicals; C043055:gallium arsenide; D005708:Gallium; D000535:Aluminum
keywords: GaAs; mobility; modulation doping; photoconductivity; photoluminescence; surface plasmon; terahertz spectroscopy