A technique for creating high quality Schottky barrier devices in doped (e.g., Li+) crystalline metal oxide (e.g., ZnO) comprises field-controlled diffusion of mobile dopant atoms within the metal oxide crystal lattice. When heated (e.g., above 550 K) in the presence of an electric field (e.g., bias to ground of +/−50 V) the dopant atoms are caused to collect to form an ohmic contact, leaving a depletion region. The size of the depletion region controls the thickness of the Schottky barrier. Metal-semiconductor junction devices such as diodes, photo-diodes, photo-detectors, MESFETs, etc. may thereby be fabricated.