Method of field-controlled diffusion and devices formed thereby
View Patent ↗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.
1. A method of fabricating a metal-semiconductor Schottky-barrier transistor structure, comprising:
providing a metal oxide structure having mobile p-type dopant ions introduced therein;
forming first, second, and third contact structures on the surface of said metal oxide structure wherein the second contact is located physically between, but spaced apart from, the first and third contact structures;
elevating the temperature of said metal oxide structure;
creating an electric field within a first region and a third region of said metal oxide structure by establishing a voltage potential between the first and second contact structures and the second and third contact structures, respectively, said electric field present while said metal oxide structure is at said elevated temperature, such that said mobile p-type dopant ions are caused to selectively migrate from a second region of said metal oxide structure which is substantially outside of said electric field toward said first and third regions of said metal oxide structure proximate said first and third contact structure; and
removing said electric field and lowering the temperature of the metal oxide structure such that the migrated dopant ions remain in the locations to which they have migrated;
whereby at least a portion of said second region becomes one portion of a Schottky barrier, and further whereby exposure of the structure to light in order to cause the mobile p-type dopant atoms to migrate is not performed.
2. The method of claim 1 wherein the step of creating an electric field in the metal oxide structure while the structure is at an elevated temperature results in the formation at the interface between the contact structures and the metal oxide structure at the first and third regions Ohmic contacts, and at the second region a Schottky contact.
3. The method of claim 1 wherein the first and third region provides a source region and a drain region of the transistor, respectively, and the second region provides a gate region for the transistor.