Development of fabrication technology for the permeable base transistor

Efforts during the first year of this contract have concentrated on the development of the key processes required for fabrication of the permeable base transistor: sub-micrometer lithography and epitaxial overgrowth. Electron beam lithography was used, with a dry-process resist and ion milling, to produce 0.25 micrometer lines. The arsenic trichloride epitaxial process was used to embed metal structures in a single crystal of gallium arsenide. High-resolution electron microscopy revealed that the epitaxial overgrowth was imperfect, leaving voids in the single crystal which are often too small to be resolved using conventional electron microscopy.