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.
We have fabricated a device which includes two lateral p-n junctions on an n-type GaAs/Al0.33Ga0.67As heterostructure. A section of the n-type material has been converted to p-type by removing dopants and applying a voltage to a gate placed in this region. Controlled electroluminescence from both of the p-n junctions has been demonstrated by varying the applied bias voltages. An emission peak with a width of ∼ 8 nm is observed around 812 nm. The electroluminescence seen from both junctions is considered to originate from the GaAs quantum well layer in the device. The lithographic techniques that we have developed are compatible for further integration of gated quantum devices such as single-electron pumps to build on-demand single-photon sources.
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