Ohmic nanocontacts to GaAs using undoped and p-doped layers of low-temperature-grown GaAs

Abstract

The development and characterization of high-performance nanocontacts to n-GaAs are reported. The nanocontacts can be made to both undoped and p-doped low-temperature-grown GaAs ͑LTG:GaAs͒ cap layers. The geometry of the nanocontact is well characterized and requires the deposition of a 4 nm single-crystalline Au cluster onto an ohmic contact structure which features a chemically stable LTG:GaAs surface layer prepared using an ex situ chemical self-assembly technique. A self-assembled monolayer of xylyl dithiol (HS-CH 2 -C 6 H 4 -CH 2 -SH) is required to provide mechanical and electronic tethering of the Au cluster to the LTG:GaAs surface. For the case of an undoped LTG:GaAs cap layer, a specific contact resistance of 1ϫ10 Ϫ6 ⍀ cm 2 and a current density of 1ϫ10 6 A/cm 2 have been measured from scanning tunneling microscopy. When a p-doped LTG:GaAs cap layer is used, the corresponding values are 1ϫ10 Ϫ7 ⍀ cm 2 and 1 ϫ10 7 A/cm 2 , respectively. Improved surface stability as evidenced by a lower oxidation rate for p-doped LTG:GaAs provides a natural explanation for the higher-quality ohmic contact properties of the nanocontact to the p-doped LTG:GaAs cap layer.

Interface and contact structures for nanoelectronic devices using assemblies of metallic nanoclusters, conjugated organic molecules and chemically stable semiconductor layers

“…2, values of ρ c of approximately 1 × 10 −7 cm 2 and the maximum current density of approximately 1 × 10 7 A cm −2 are obtained. Both of these values are comparable to the values achieved in high-quality large-area ohmic contacts to n-type GaAs [16]. In this case, the measurement system limits the minimum ρ c which can be resolved, so the contact resistance may be somewhat lower than this value.…”

“…The current-voltage characteristics of the nanocontact structures have been measured using ultra-high-vacuum (UHV) STM current-voltage spectroscopy in the near-contact regime, i.e. a regime in which the resistance between the STM tip and the cluster is reduced by bringing the tip in close proximity to the cluster [15,16]. STM tips used in this study have typical end shapes with diameters less than 15 nm, as observed from TEM micrographs.…”

“…In these studies, a controlled area nanocontact is formed by a single crystal, 4 nm diameter Au nanocluster deposited on the GaAs surface, which has previously been coated with a SAM of XYL. Details of the procedure have been presented elsewhere [15,16]. The area of the conducting path for the nanocontact (1 × 10 −13 cm 2 ) is defined by the area of a facet on the 4 nm diameter cluster.…”

Self-assembled metal/molecule/semiconductor nanostructures for electronic device and contact applications

“…27 Using this maximum current value, we determined an upper bound for r c of ~1 ¥ 10 -7 W·cm 2 and a lower bound for J max of ~1 ¥ 10 7 A/cm 2 for the nanocontact with the p-doped LTG:GaAs cap layer. 27 The difference in the contact properties between the samples can be qualitatively explained by the better surface stability of p-doped LTG:GaAs and the presence of mid-gap states near the Fermi level in this material.…”

“…27 Using this maximum current value, we determined an upper bound for r c of ~1 ¥ 10 -7 W·cm 2 and a lower bound for J max of ~1 ¥ 10 7 A/cm 2 for the nanocontact with the p-doped LTG:GaAs cap layer. 27 The difference in the contact properties between the samples can be qualitatively explained by the better surface stability of p-doped LTG:GaAs and the presence of mid-gap states near the Fermi level in this material. 26,27 The I(V) shape difference between measurements over the cluster and over the XYL-coated surface can also be qualitatively explained by the work function difference between the Au nanocluster and the Pt/Ir tip and the resulting surface barrier height difference between the two cases.…”