Researchers at UC San Diego in collaboration with Peking University have successfully synthesized p-type zinc oxide (ZnO) nanowires using simple, low-cost chemical vapor deposition (CVD) techniques.
The paper's authors suggest this could pave the way to ZnO LEDs that are less expensive than today's blue, green and white LEDs that are fabricated using gallium nitride (GaN)-based materials. Of course, ZnO LEDs have many years of development ahead before they can match the performance of GaN devices.
LEDs require both p-type (positively-charged) and n-type (negatively-charged) material. The fabrication of n-type ZnO nanowires (nanometer-scale cylinders of material that transport negative charge) has not been a problem, but this is the first instance of successful fabrication of p-type nanowires.
Deli Wang, an electrical and computer engineering professor from UCSD’s Jacobs School of Engineering, said, "Zinc oxide is a very good light emitter. Now that we have p-type zinc oxide nanowires, the opportunities for LEDs and beyond are endless."
Other groups have demonstrated p-type conduction in ZnO thin films and made ZnO thin film LEDs. However, Wang claims that using ZnO nanowires rather than thin films to make LEDs would be less expensive and could lead to more efficient LEDs.
The starting materials and manufacturing costs for ZnO LEDs are far less expensive than those for GaN-based LEDs. To make the p-type ZnO nanowires, the engineers doped ZnO crystals with phosphorus using a simple CVD technique that is less expensive than the metal organic chemical vapor deposition (MOCVD) technique routinely used to synthesize GaN-based LEDs. In the future, Wang expects to cut costs even further by making p-type and n-type ZnO nanowires from solution.
Wang has filed a provisional patent for p-type ZnO nanowires and his lab at UCSD is currently working on a variety of nanoscale applications. Having both n- and p-type ZnO nanowires – complementary nanowires – could also be useful in a variety of applications including transistors, spintronics, UV detectors, nanogenerators, and microscopy. In spintronics applications, researchers could use p-type ZnO nanowires to make dilute magnetic semiconductors by doping ZnO with magnetic atoms, such as manganese and cobalt, Wang explained.
The research entitled "Rational Synthesis of P-type Zinc Oxide Nanowire Arrays Using Simple Chemical Vapor Deposition" was published online in Nano Letters on December 29, 2006. Funding was provided by the Office of Naval Research, the National Science Foundation and Sharp Labs of America.