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March 9th, 2012

New era in oxide electronics? Single oxide p-n junction demonstrated

Published on March 9th, 2012 | By: pwray@ceramics.org

Schematic of laser induced pn junctions in nickel oxide single crystal films integrated with silicon or sapphire substrates by domain matching epitaxy. Credit: J. Narayan, U.S. Patent # 6,955,985)

A group at North Carolina State University led by Jagdish Narayan, an ACerS member and well-known expert in advanced materials processing, says it has accomplished a major milestone by producing p-type conduction and n-type conduction in a single oxide material, an achievement that may open the door to power-tolerant oxide-based functional electronic devices.

In a new paper in Journal of Applied Physics, Narayan’s group reports on some of the “systematic changes in structural, electrical and optical properties of NiO thin films on c-sapphire introduced by nanosecond ultraviolet excimer laser pulses.” The paper is titled, “Controlled p-type to n-type conductivity transformation in NiO thin films by ultraviolet-laser irradiation” (doi:10.1063/1.3671412).

If I understand their work correctly, they first built a nickel oxide single crystal thin film on the sapphire. NiO naturally acts as a p-type semiconductor. Then, using a pulsed ultraviolet excimer laser with a specific energy density, they were able to convert the top layer of the NiO to have n-type behavior, effectively creating a custom-crafted pn interface. They believe the laser induces Ni0-type defects in the film. The conversion of the n-type material can be reversed by annealing in the presence of oxygen.

In an NCSU news release, Narayan explained the significance of this ability, noting, “This spatial and temporal selectivity provides unprecedented control to ‘write’ pn junctions by laser beams and create ultra high-density device features for oxide electronics. … This is a new era in oxide electronics.”

Narayan, who also serves as director the the NSF Center for Advanced Materials and Smart Structures, says previous attempts to build pn heterojunctions with oxides (e.g., p-type NiO/n-type ZnMgO) were not very successful because they were based on using different oxides. “We avoided this problem by using the same material for p– and n-type conduction,” he says.

The authors say in their paper that the ability to convert  p-NiO to n-type by controlled high power pulsed laser irradiation “brings in the possibilities for the next-generation of efficient pn junction and complemen- tary oxide-based transistor applications in oxide electronics. Some of the features expected for oxide devices include:

  • Higher voltage tolerances;
  • More stability at high temperatures;
  • Oxygen tolerance, opening up gas and air monitoring applications;
  • The ability to make transparent electronics.

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