New research findings open door to zinc-oxide-based UV lasers, LED devices

Apr 23, 2013 by Matt Shipman

(Phys.org) —Researchers from North Carolina State University have solved a long-standing materials science problem, making it possible to create new semiconductor devices using zinc oxide (ZnO) – including efficient ultraviolet (UV) lasers and LED devices for use in sensors and drinking water treatment, as well as new ferromagnetic devices.

"The challenge of using ZnO to make these devices has stumped researchers for a long time, and we've developed a solution that uses some very common elements: nitrogen, hydrogen and oxygen," says Dr. Lew Reynolds, co-author of a paper describing the research and a teaching associate professor of at NC State. "We've shown that it can be done, and how it can be done – and that opens the door to a suite of new and LED technologies," says Dr. Judith Reynolds, a research scientist at NC State and lead author of the paper.

To make laser and LED technologies, you need both "n-type" and "p-type" materials. N-type materials contain an abundance of . P-type materials have "holes" that attract those free electrons. But the holes in the p-type materials have a lower , which means that electrons release their excess energy in the form of light as they travel from the n-type material to the p-type material. The shedding of excess energy at the so-called "p-n junction" is what produces light in lasers and LED devices.

Researchers have been interested in using ZnO to create these devices because ZnO produces UV light, and because ZnO can be used to make devices with relatively fewer unwanted defects than other UV emitters– which means the resulting lasers or LEDs would be more energy efficient.

However, researchers had been unable to consistently produce stable p-type materials out of ZnO. Now researchers have solved that problem by introducing a specific "defect complex," via a unique set of growth and annealing procedures, in the ZnO. The defect complex looks different from a normal ZnO molecule. The zinc atom is missing and a nitrogen atom (attached to a hydrogen atom) substitutes for the oxygen atom. These defect complexes are dispersed throughout the ZnO material and serve as the "holes" that accept the electrons in p-type materials.

Not only does the research illustrate how to create p-type materials from ZnO, but the defect complex allows the ZnO p-n junction to function efficiently – and produce UV light – at room temperature.

Explore further: Unexpected new mechanism reveals how molecules become trapped in ice

More information: The paper, "Shallow acceptor complexes in p-type ZnO, " is published online in Applied Physics Letters. apl.aip.org/resource/1/applab/v102/i15/p152114_s1

Abstract
We show that N-doped ZnO films grown on sapphire can exhibit significant (~1018 cm–3) room-temperature p-type behavior when sufficient nitrogen (N) is incorporated and the material is annealed appropriately. Substitutional N on the oxygen (O) sublattice is a deep acceptor; however, shallow acceptor complexes involve N, H and zinc vacancies (VZn). Combining secondary ion mass spectrometry, Raman-scattering, photoluminescence, and Hall-effect data, we establish the evolution of N from its initial incorporation on a Zn site to a final shallow acceptor complex VZn_NO_H+ with an ionization energy of ca. 130 meV. This complex is responsible for the observed p-type behavior.

Related Stories

Exposing ZnO nanorods to visible light removes microbes

May 12, 2011

The practical use of visible light and zinc oxide nanorods for destroying bacterial water contamination has been successfully demonstrated by researchers at the Asian Institute of Technology (AIT). Nanorods grown on glass ...

Research opens doors to UV disinfection using LED technology

May 14, 2012

Research from North Carolina State University will allow the development of energy-efficient LED devices that use ultraviolet (UV) light to kill pathogens such as bacteria and viruses. The technology has a wide array of applications ...

Nanowires exhibit giant piezoelectricity

Jan 26, 2011

Gallium nitride (GaN) and zinc oxide (ZnO) are among the most technologically relevant semiconducting materials. Gallium nitride is ubiquitous today in optoelectronic elements such as blue lasers (hence the blue-ray disc) ...

Recommended for you

'Pixel' engineered electronics have growth potential

Sep 29, 2014

(Phys.org) —A little change in temperature makes a big difference for growing a new generation of hybrid atomic-layer structures, according to scientists at Rice University, Oak Ridge National Laboratory, ...

2-D materials' crystalline defects key to new properties

Sep 24, 2014

Understanding how atoms "glide" and "climb" on the surface of 2D crystals like tungsten disulphide may pave the way for researchers to develop materials with unusual or unique characteristics, according to an international ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

dirk_bruere
not rated yet Apr 23, 2013
And the efficiency is...?