This VG V80H growth chamber was manufactured in 1986, it has been comprehensively updated and modified with high uniformity K-cells, soft action shutters and a single foil substrate heater. It is pumped by a 400 l/s ion pump and a Leybold 1500 l/s cryopump, liquid nitrogen is continuously supplied to the cryopanel. It has conventional solid sources comprising Gallium, Aluminium, Indium, Arsenic and Antimony, a Silicon K-cell provides n-type doping. This chamber is also fitted with a novel focussed ion beam system which is used to dope the growing crystal in selected areas using silicon ions. The growth chamber shutters and K-cells are controlled by an Episoft computer system.

The molecular beam fluxes are measured by an ion gauge mounted on the sample manipulator. In addition oscillations in the apparant temperature of the growing substrate (as observed by an Ircon "V" series pyrometer) are used to accurately determine the growth rate.

Growth in the "C" chamber is divided amongst several projects. GaAs/AlGaAs heterostructures are grown for the programmes of work involving the high resolution ion beam system and the surface decontamination system. Low temperature electron mobilities of around 2E6 are routinely achieved. In addition the GaSb/AlSb/InAs material system is being used for the growth of novel electron-hole structures.

The in-situ focussed ion beam system is mounted in the central port opposite the growing wafer. It has a Au/Si/Be alloy source with a mass filter which is used to select the Si or Be species. These ions are emitted from the gun at 2keV and projected towards the growing wafer, the position of the focussed beam is controlled by scanning plates. The sample itself is floated at a voltage of 1.95keV which retards the ions and they impinge on the growing surface with an energy of 50eV. At energies of this magnitude the silicon or beryllium ions behave in a similar way to a convention thermal source. Using this focussed ion beam, which has a lateral resolution of around 50 microns, lateral dopant patterning is achieved. This system is curently being used to fabricate novel electronic devices.

Click here for close-up view of the focused ion gun.