Bright ideas to improve LED lighting performance

Posted: January 29, 2018

In a preview of an article accepted by Nature's Light: Science & Applications journal, researchers from The Ohio State University, Wright State University and the Naval Research Laboratory describe a promising new semiconductor LED made with gallium nitride-based materials that could boost wall socket efficiency by reducing energy losses and self-heating.

If this new technology can be harnessed for large light output, the breakthrough could enhance LED solid-state lighting without a significant change to the existing LED manufacturing facility.

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The new LEDs could provide more light with less voltage and resistance than in conventional gallium nitride (GaN) LEDs, thereby boosting the overall lumens per watt output and avoiding the efficiency droop that plagues high brightness LEDs.

One way the researchers overcome this problem is by completely removing all p-type doping in GaN, which historically is hard to dope and leads to a high series resistance.

The team includes Ohio State Electrical and Computer Engineering Prof. Paul Berger and Postdoc Researcher Tyler Growden, Wright State's Elliott Brown and Weidong Zhang, and David Storm and David Meyer at the Naval Research Laboratory.

The key to the team's discovery is the ability to create "holes" for radiative recombination with electrons by quantum-mechanical tunneling, not by p-doping. The tunneling occurs by the Zener mechanism, delivering the holes to the zone of recombination, mitigating the need for clumsy p-type ohmic contacts and resistive p-type semiconductor injectors.

Their discovery was made while advancing resonant tunneling diodes (RTD) in the gallium nitride system for the Office of Naval Research under Program Officer Paul Maki. As reported in the August 2016 issue of Applied Physics Letters, their effort also established a stable GaN-based RTD platform for high microwave power generation and potentially terahertz sources.

The fundamental science behind this advancement is the utilization of the extremely high electric fields induced by the polarization effects within wurtzite GaN-based heterostructures. These high fields allow the new device to not only inject electrons across a classic RTD double-barrier structure in the conduction band, but also simultaneously inject holes by Zener tunneling across the GaN band gap into the valence band. Thus, the new LED uses only n-type doping, but includes bipolar tunneling charges to create the new LED light source.

To be useful for commercialization, the team is working to balance the injected electron and hole ratio to create and therefore deliver up to one emitted photon for each injected electron.

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