GAAS ALGAAS DEVICE FABRICATION USING MBE GROWTH AND IN-SITU FOCUSED ION-BEAM LITHOGRAPHY/

We describe a versatile technique for the fabrication of 3-D patterned III-V semiconductor devices, using molecular beam epitaxial (MBE) gro wth and high energy focused ion beam (FIB) lithography. Ohmic contacts can be made independently to a 2DEG and a closely separated n(+) GaAs backgate by first implanting regions of the backgate which will event ually lie directly below the ohmic contacts to the 2DEG, rendering the m highly resistive. Conventional technology can then be used to form o hmic contacts to the 2DEG, resulting in very high device yields (>80%) , compared to those utilising a shallow ohmic contacting process. Furt her, no deterioration of the 2DEG quality is observed, despite the gro wth interruption during ion beam patterning. This technique has been f urther developed to pattern the back-gate into multiple conducting and insulating regions, e.g. a split-gate geometry patterned on the back- gate or, using a combination of FIB patterned backgates and Schottky f ront-gates, the formation of independent contacts to two closely space d ( <10 nm) 2DEGs.