Multiterminal epitaxial tungsten nanostructures on MgO/GaAs(001) substrates: Temperature effects in ballistic electron transport

High-quality single-crystalline multiterminal tungsten nanostructures were fabricated on MgO/GaAs (001) substrates using subtractive lithography. Single-crystalline tungsten films with a thickness of d = 80 nm and low roughness were grown using sequential epitaxy of MgO (001) and W (001) layers on GaAs (001) via pulsed laser deposition. The temperature dependence of bridge-type nanostructure electron conductivity indicates that they are high-quality metal conductors. The electron mean free path reached 760 nm at low temperatures and was approximately an order of magnitude greater than the tungsten film thickness. Strong non-local effects resulting from ballistic electron transport were observed in the multiterminal cross-type W (001) nanostructures with an arm width Wc = 400 nm below T = 80 K. Such effects can be explained by the exponential damping of ballistic properties of nanostructures as a function of the electron mean free path in the wide temperature range 4.2–100 K. Simulations predict that the ballistic effects in such nanostructures can be significant even at room temperature with an arm width approaching 10 nm and a size ratio of Wc/d ∼ 1.