Cheaper LEDs from nanowire breakthrough
IN A Light Emitting Diode (LED), when an electron meets a `hole,' it falls into a lower energy level and releases energy in the form of a photon of light.
Now, Deli Wang, an electrical and computer engineering professor from the University of California, San Diego (UCSD)'s Jacobs School of Engineering, and colleagues at UCSD and Peking University, report synthesis of high quality p-type zinc oxide nanowires in a paper published online by the journal Nano Letters.
These nanoscale cylinders transport positive charges, according to a UCSD press release. To build an LED, you need both positively and negatively charged semiconducting materials.
The synthesised so-called `p-type ZnO nanowires' are endowed with a supply of positive charge carrying `holes' that, for years, have been the missing ingredients that prevented engineers from building LEDs from ZnO nanowires.
Relative overabundance
For years, researchers have been making electron-abundant n-type ZnO nanowire crystals from zinc and oxygen.
Conductive properties
Missing oxygen atoms within the regular ZnO crystal structure create relative overabundances of zinc atoms and give the semiconductors their n-type, conductive properties.
The lack of accompanying p-type ZnO nanowires, however, has prevented development of a wide range of ZnO nanodevices.
To make the p-type ZnO nanowires, the engineers doped ZnO crystals with phosphorus using a simple chemical vapour deposition technique that is less expensive than the metal organic chemical vapour deposition (MOCVD) technique often used to synthesize the building blocks of gallium nitride LEDs.
Adding phosphorus atoms to the ZnO crystal structure leads to p-type semiconducting materials through the formation of a defect complex that increases the number of holes relative to the number of free electrons.
A variety of applications
The starting materials and manufacturing costs for ZnO LEDs are far less expensive than those for gallium nitride LEDs.
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. — Our Bureau
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