Fabrication of in situ Ohmic contacts patterned in three dimensions using a focused ion beam during molecular beam epitaxial growth

Focused ion beam doping during molecular beam epitaxial (MBE) growth is a novel technique that allows the in situ fabrication of unique three-dimensional semiconductor structures with doping profiles unobtainable using standard planar lithography. Conventional MBE growth uses a thermal Si effusion cell as the dopant source during two-dimensional layer growth of III–V semiconductor material. In the technique described here, a scanning Si focused ion beam (FIB) has been added onto the growth chamber to introduce the dopant atoms selectively in a maskless lithographic process. As the FIB is rastered in the xy plane under computer control during crystal growth in the z direction, it is possible to generate specific three-dimensional dopant patterns embedded within the semiconductor. Furthermore, the patterned semiconductor crystal requires no post growth anneal as the dopant ions are decelerated by a retarding electric field on the sample. The dopant is thus deposited on the epilayer surface rather than impin...