Oxide Electronics

Oxides are a very large class of materials that demonstrate almost every known electromagnetic property known to science – giant magnetoresistance (GMR), ferroelectricity, ferromagnetism, superconductivity, and ofcourse semiconductivity. Yet, oxide thin-films have been primarily used only as insulators in traditional devices. With Moore’s law coming to an end, one way to increase performance and functionality is to exploit oxides for novel properties.

Oxide semiconductors have been very succesfully demonstrated for thin-film transistors and as transport layers for solar cells. Unfortunately, most of the promising oxide materials conduct only electrons. Very few metal-oxides with reasonable hole-mobility have been demonstrated. The reasons for low hole-mobility are hypothesized to be fundamental – valence bands of most oxides are inherently dispersive. However there are some examples of oxides which show reasonable hole-mobility, e.g. Cu2O and its derivatives. Using a combinaion of chemical vapor deposition and novel precursors, we are attempting to demonstrate better p-type oxide films.

While most oxides are wide bandgap materials, some oxides do have bandgap small enough to absorb visible light (1.5-2.0 eV). Yet, all-oxide solar cells are woefully inefficient; state-of-the-device, using epitaxial Bi$_2$FeCrO$_6$ on STO substrates, is only 8%. For thin-film all-oxide solar cells the record is 5.38%, achieved by a Ga2O3-Cu2O heterojunction fabricated on oxidized Cu sheet. Using a combination of first-principle calculations, better thin-film deposition, and innovative device design, we hope to attain efficiency of >10% in oxide thin-film PV.

Finally, ferroelectric oxides have been shown for non-volatile memory applications. Unfortunately, almost all demonstrations use oxide-substrates that are expensive and incompatible with traditional CMOS manufacturing. Our collaborators have recently demonstrated technology to grown BTO and STO epitaxial on silcon. Using this platform we are trying to demonstate ferroelctric memory on Si wafers.

Publications

All-oxide solar cells are attractive due to their stability, low cost and ease of fabrication. Very few oxide-absorbers are known and …

Metal-oxide semiconductors are attractive as solar absorbers because they are abundant, stable, environmentally-safe, and low-cost. …

Talks

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