MBE Regrowth over a Patterned ∂-doped backgate

Using in situ hydrogen radical decontamination we have successfully grown a 2DEG 160 Å from an ex situ patterned GaAs interface with a mobility of 390,000 cm²/Vs at a carrier concentration of 8.2 10¹¹ cm^-2. For a regrowth interface/2DEG separation of 300 Å, mobilities >1x10⁶ cm²/Vs are achieved. We can modulate the potential within the regrown 2DEG by applying biases to delta-doped layers incorporated into the first growth. The lengthscale of this modulation is controlled by the projected width of the doped layer (<600 Å). We demonstrate that this technique can be used to create FET structures with very short gate lengths. And finally we present electron transport data from a quasi-ID wire device which show conductance plateaux which are interpreted in terms of quantised ballistic conductance.