Ohmic contacts for GaAs based nanocolumns

Abstract

Nonalloyed ohmic contacts with lateral dimensions in the sub‐100 nm range have been processed and characterized. The contacts are suitable for the fabrication of GaAs/AlGaAs nanocolumns designed in a ‘top down’ approach. They are realized on n‐type GaAs using a thin low‐temperature grown GaAs cap layer and Ti/Au metallization. For the lateral patterning of the nanoscaled ohmic contacts, electron‐beam lithography based on Hydrogen Silsesquioxan (HSQ) negative resist is used, followed by sputtering and plasma etching of the metals. The I –V characteristics show ohmic contact behavior and demonstrate the scaling of the proposed contacts down to 50 nm lateral dimension. The specific contact resistance is situated in the range of 1–2 × 10–5 Ω cm2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanoscale charge transport measurements using a double-tip scanning tunneling microscope

“…This asymmetry between positive and negative voltages can be explained by an increasing non-Ohmic behavior of the nanocontact on top of the RTD. 26 The current peaks on the positive voltage side are highly pronounced. The device quality of a RTD is expressed by a peak-to-valley current ratio ͑PVR͒.…”

“…On top of the devices, a layer combination of low-temperature-grown GaAs, titanium, and 30 nm gold provides an Ohmic contact to the GaAs-based nanocolumn. 26 In Fig. 2͑a͒, a SEM image of the columns with a lateral width of 100 nm and a height of 200 nm is shown.…”

“…It was found that the contact resistance becomes negligible with respect to the intrinsic resistance of the nanocolumn if a penetration depth of 10-20 nm has been reached. 26 For the presented measurements, the penetration depth of 30 nm was used, i.e., the complete thickness of the gold layer. After establishing the Ohmic contact, a voltage ramp between the STM tip and the backside contact of the sample was applied.…”

Gate-controlled quantum collimation in nanocolumn resonant tunneling transistors

“…Even if the specific contact resistance (1 × 10 −5 cm −2 ) does not reach the low value of standard ohmic contacts on GaAs, the value is independent of the contact area. This means that the contact is fully scalable with the feature size even in the nanometer range [12]. The processing of the RTT necessitates accurate alignment during the electron-beam (EB) lithographic steps.…”