Dopant patterning in three dimensions during molecular beam epitaxial growth using anin-situfocused ion gun

Conventional molecular beam epitaxial (MBE) growth of III-V semiconductor material systems use a thermal silicon effusion cell as the n-type dopant source. In the technique described here, the thermal source is replaced with a scanning Si focused ion gun. It is therefore possible to directly write dopant patterns into the semiconductor waferit as it is being grown. The precise control over the elemental composition in the growth (z) direction permitted by MBE, combined with high spatial resolution of the focused dopant ion beam in the lateral (xy) plane, allows direct registration of fully integrated, three-dimensional semiconductor structures and devices otherwise unobtainable via conventional lithographic techniques. In this paper, we present electrical measurements of high mobility GaAs/AlGaAs modulation doped heterostructures fabricated using this technique.Fabrication of novel undoped channel FET structures is also discussed, where the dopant beam is used to form extended contacts to the induced electron gas. FET action is demonstrated for the first time using this technique, eliminating the constraint for self-alignment in undoped structures.