Scientists Create Building Blocks For Future GaN Power Switches

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Gallium nitride (GaN) power diodes capable of serving as the building blocks for future GaN power switches are recently created by a team of engineers from Cornell University, the University of Notre Dame and the semiconductor company IQE. Nearly all electronics and electricity distribution infrastructures, including electric motors, power adapters, solar power plants and smart grids, can benefit from a gallium nitride (GaN) power diode

Power-semiconductor devices are a critical part of the energy infrastructure, all electronics rely on them to control or convert electrical energy. Silicon based semiconductors are rapidly approaching their performance limits within electronics, so materials such as GaN are being explored as potential replacements that may render silicon switches obsolete.

Many researchers around the globe are working to find ways to make GaN materials reliable for use within future electronics. Due to the presence of defects with high concentrations in typical GaN materials today, GaN based devices often operate at a fraction of what GaN is truly capable of.

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So the team zeroed in on devices based on GaN with record-low defect concentrations to probe GaN’s ultimate performance limits for power electronics. They describe their results in a paper in the journal Applied Physics Letters, from AIP Publishing.

“Our engineering goal is to develop inexpensive, reliable, high-efficiency switches to condition electricity from where it’s generated to where it’s consumed within electric power systems, to replace generations-old, bulky, and inefficient technologies. GaN-based power devices are enabling technologies to achieve this goal”, said Zongyang Hu, a postdoc at Cornell University.

The team examined semiconductor p-n junctions, made by joining p-type (free holes) and n-type (free electrons) semiconductor materials, which have direct applications in solar cells, light-emitting diodes (LEDs), rectifiers in circuits, and numerous variations in more complex devices such as power transistors. “For our work, high-voltage p-n junction diodes are used to probe the material properties of GaN,” Hu said.

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To describe how much the device’s current-voltage characteristics deviate from the ideal case in a defect-free semiconductor system, the team uses a ‘diode ideality factor.’ This is an extremely sensitive indicator of the bulk defects, interface and surface defects, and resistance of the device.

Researchers used a parameter “Shockley-Read-Hall (SRH) recombination lifetime” to effectively describe the defect level in a material . SRH lifetime is the averaged time it takes injected electrons and holes in the junction to move around before recombining at defects. The lower the defect level, the longer the SRH lifetime. It’s also interesting to note that for GaN, a longer SRH lifetime results in a brighter light emission produced by the diode.

For making breakthrough contributions to the field of GaN-based LEDs, scientists were awarded Nobel prize in 2014. Though operating at compromised conditions, GaN LEDs are helping to shift the global lighting industry to a much more energy-efficient, solid-state lighting era.

The work led by Xing at Cornell University is said to be the first report of GaN p-n diodes with near-ideal performance in all aspects simultaneously: a unity ideality factor, avalanche breakdown voltage and about a two-fold improvement in device figure-of-merits over previous records.

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