Specifications :

• UHV focused ion column with Ga⁺ source
• Beam Energy 10 - 50 kV
• Spot size < 100 nm
• Vibration isolated UHV sample chamber with UHV interconnects to MBE system
• Laser interferometer controlled stage with in-vacuo stepper motors
• Computer control allowing lithography of complex devices with stitching of fields for large devices and step and repeat across wafer

Operating Parameters:

• Typical sample current 100 pA
• Using a dose of ~10¹³ ions cm^-2 a 50 nm n⁺ layer becomes highly resistive
• A wafer of 36 devices takes approximately six hours to pattern

Typical Device Fabrication Procedure:

• A 50 nm n⁺ layer is grown on a S.I. GaAs substrate by MBE
• The wafer is transferred under UHV to the FIB system, where it is patterned into conducting and insulating regions
• The wafer is returned to the MBE chamber for growth of the remaining structure e.g. 2x2DEG
• The wafer is removed from the MBE system for normal processing

Devices Fabricated:

• Independent contacts to coupled gases using a combination of patterned back and front gates
• Split back-gated electron gases
• Hot electron transistors (HETs)