Top-down, in-plane GaAs nanowire MOSFETs on an Al2O3 buffer with a trigate oxide from focused ion-beam milling and chemical oxidation.

The top-down fabrication of an in-plane nanowire (NW) GaAs metal-oxide-semiconductor field-effect transistor (MOSFET) with a trigate oxide implemented by liquid-phase chemical-enhanced oxidation (LPCEO) is reported. A 2 µm long channel having an effective cross section ∼70 × 220 nm(2) is directly fabricated into an epitaxial n (+)-GaAs layer. This in-plane NW structure is achieved by focused ion beam (FIB) milling and hydrolyzation oxidation resulting in electronic isolation from the substrate through a semiconductor-on-insulator structure with an n (+)-GaAs/Al2O3 layer stack. The channel is epitaxially connected to the µm-scale source and drain within a single layer for a planar MOSFET to avoid any issues of ohmic contact and LPCEO to the NW. To fabricate a MOSFET, the top and the two sidewalls of the in-plane NW are oxidized by LPCEO to relieve the surface damage from FIB as well as to transform these surfaces to a ∼15 nm thick gate oxide. This trigate device has threshold voltage ∼0.14 V and peak transconductance ∼35 µS µm(-1) with a subthreshold swing ∼150 mV/decade and on/off ratio of drain current ∼10(3), comparable to the performance of bottom-up NW devices.