Quasi one-dimensional transport in single GaAs/AlGaAs core-shell nanowires

Abstract

We present an original approach to fabricate single GaAs/AlGaAs core-shell nanowire with robust and reproducible transport properties. The core-shell structure is buried in an insulating GaAs overlayer and connected as grown in a two probe set-up using the highly doped growth substrate and a top diffused contact. The measured conductance shows a non-ohmic behavior with temperature and voltage-bias dependences following power laws, as expected for a quasi-1D system.Semiconductor nanowires (NWs) are promising candidates for the realization of innovative nano-devices for electronics as well as for photonics [1]. They also represent a new test bed system in semiconductor material science to explore the fundamental properties of 1D systems [2]. Usual fabrication of such nano-objects by lithography and etching techniques is limited by surface damage and roughness which, at very small sizes, have a dominant effect on their physical properties. In contrast, the metal particle-mediated vapor-liquid-solid (VLS) growth mechanism allows to obtain NWs of high crystalline quality with uniform nanometer-scale diameters. Moreover, this bottom-up approach gives the possibility to achieve heterostructure material combinations that are not possible in bulk semiconductors [3]. In particular core-shell heterostructures formed by the growth of crystalline overlayers around the initial NW reduces surface states which can act as scattering or recombination centers [4].The GaAs/AlGaAs material system, which presents very large band offsets and small lattice mismatches, has been studied and used extensively to fabricate heterostructures with complex band engineering along the growth direction of the crystal [5].The modulation-doping concept [6] was first implemented in this system and high electron mobility transistors were demonstrated [7]. Nowadays, a low-temperature electron mobility of several 10 6 cm 2 /V.s is currently obtained in 2D structures [8]. To achieve 1D carrier confinement it is thus of particular interest to use the wellknown GaAs/AlGaAs system and realize core-shell NW by wrapping a GaAs NW core with an AlGaAs shell layer. VLS technique has been used to produce such GaAs/AlGaAs core-shell NWs[9-11], but up to now these heterostructures have been mainly characterized by photoluminescence [11,12] due to difficulty in achieving good electrical contacts.The standard technique to contact a NW is to mechanically detach them from the growth substrate, and after dispersion on an insulating substrate, to evaporate contact pads by lithography. This technique may suffer from the random positioning of the wires, from the oxidation of the AlGaAs shell and from the presence of pinned charges in the insulating subtrate. In this letter, we present an original method using molecular beam epitaxy (MBE) and electron-beam lithography (EBL) to achieve modulation-doped GaAs/AlGaAs core-shell NWs embedded in a GaAs matrix. The NWs are individually connected directly on their growth substrate and show a small contact resistance enabling low-te...

Free standing modulation doped core–shell GaAs/AlGaAs hetero‐nanowires

“…If nanowires are combined with modulation doping further perspectives in nanoelectronics might be possible. Recently, a first report on modulation doping in core-shell nanowires buried in a GaAs matrix was published [6] with indications of the formation of a one-dimensional (1D) electron channel. However, only two terminal differential resistance was measured and gate control of the carrier density was not possible.…”

Preparation of Ohmic contacts to GaAs/AlGaAs-core/shell-nanowires

“…An elegant solution of this problem is to epitaxially coat the nanowire by a shell semiconductor with a higher energy band gap. [3][4][5][6][7][8][9][10] Here, AlGaAs is the perfectly suitable shell material as it supplies charge carriers to the GaAs core by modulation doping [10][11][12] as well as preserves the carriers from the direct influence of the surface defects without additionally introduced strain due to the lattice matching between GaAs and AlGaAs.…”

Properties and tailoring of the ubiquitous core–shell p–n junction in semiconductor nanowires by δ‐doping

“…Modulation‐doping was proposed by Dingle et al 14 as a way to improve the properties of semiconductors. More recently δ‐doped GaAs/AlGaAs core–shell NWs were grown by Lucot et al 15 who suggested that δ‐doping is the most promising way of controlling the carrier concentration in semicon‐ ductor NWs. A more complex, high‐performance, multiple core shell InGaAs/InP/InAlAs/InGaAs NW employing δ‐doping was also grown very recently on Si by Tomioka et al 16.…”