Nov 20 2017
As concerns about changing to green energy for renewables and electric vehicles is mounting globally, the energy that we expend, or rather that we do not expend, is as significant as the produced renewable energy.
Therefore, solid state lighting, which is more cost-effective when compared to fluorescent and incandescent bulbs, developed by using light emitting diodes (LEDs) is hailed as the best solution. Yet, one drawback is that LEDs cannot provide greater brightness for the shorter wavelength end of lighting requirements. Moreover, the emitted short wavelengths enable the passage of white light through the familiar phosphor downconverters.
Researchers from the Ohio State University researchers, in collaboration with researchers from Wright State University and Naval Research Laboratory, have proposed a propitious and innovative semiconductor LED formed of GaN-based materials that can enhance wallsocket efficiency by minimizing self-heating and thus energy losses. The study has been published in the now online journal Light: Science & Applications October 24, 2017.
In the event that the innovative technology is adopted for higher light output, the advancement can lead to improvement in LED solid state lighting, without the need for making extensive modifications to current LED manufacturing facilities.
The innovative LEDs will be able to deliver more light at lesser voltage and resistance when compared to traditional GaN LEDs, thus increasing the overall lumens output per watt and preventing the dip in efficiency that affects high-brightness LEDs.
One method used by the researchers to solve this problem is by entirely eliminating all p-type doping in gallium nitride, which has been very difficult to dope and results in a high series resistance.
The most important factor that resulted in the findings of the researchers is the potential to develop “holes” for radiative recombination with electrons by adopting quantum-mechanical tunneling, instead of p doping. The tunneling is carried out by the Zener mechanism, carrying the holes to the recombination zone, thereby avoiding the need for using unwieldy p-type ohmic contacts as well as resistive p-type semiconductor injectors.
Paul R. Berger and Tyler A. Growden from Ohio State University; Elliott R. Brown and Weidong Zhang from Wright State University; and David F. Storm and David J. Meyer from the Naval Research Laboratory were the researchers involved in the study.
The team made their discovery while developing resonant tunneling diodes (RTDs) in the gallium nitride system for the Office of Naval Research while working under program manager Dr Paul Maki. As the team noted in the August 2016 issue of Applied Physics Letters, their work also resulted in the development of a stable GaN-based RTD platform for potential terahertz sources and high microwave power generation.
The basic science governing this breakthrough is the adoption of the exceptionally high electric fields initiated by the polarization effects within wurtzite GaN-based heterostructures. Apart from enabling the new system to inject electrons into a classic RTD double-barrier structure in the conduction band, the high fields also enable the system at the same time to inject holes across the GaN band gap, through Zener tunneling, into the valence band. Consequently, the innovative LED adopts only n-type doping and yet has bipolar tunneling charges to develop the innovative LED light source.
In order to transform the technology for commercialization, the researchers are striving to balance the ratio between the injected electron and hole to develop and hence provide one emitted photon for every injected electron.