Variable range hopping conductivity in molecular beam epitaxial InSb

Abstract

A Variable Range Hopping-VRH transport mechanism can be induced in molecular beam epitaxial, n-type doped InSb wafers with focussed Ga+ ion beam damage. This technique allows areas of wafer to be selectively damaged and then subsequently processed into gated MISmetal-insulator-semiconductor devices where a disordered, two-dimensional device can be established. At high levels of damage (dose > 1016 Ga+ ions/cm2) amorphous crystalline behaviour results with activated conductivity characteristic of a three-dimensional system with VRH below 150 K. At lower doses (1014 to 1016 Ga+ ions/cm2) a thermally activated conductivity is induced at ~ 0.9 K, characteristic of Mott phonon-assisted VRH. At 1 K the devices either conduct with conductivity > ~ (e2/h) where e is the fundamental charge and h is Planck’s constant, or are thermally activated depending on the dose level. The lightly damaged devices show weak antilocalization signals with conductivity characteristic of a two-dimensional electronic system. As the Ga+ dose increases, the measured phase coherence length reduces from ~ 500 nm to ~ 100 nm. This provides a region of VRH transport where phase-coherent transport processes can be studied in the hopping regime with the dimensionality controlled by a gate voltage in an MIS-device.