New deposition process makes LEDs brighter

Researchers at North Carolina State University (NCSU) say they have developed a new gallium nitride (GaN) deposition process that purifies high-energy semiconductor materials and reduces defect concentrations by a factor of 1000 relative to typical levels. They predict that LEDs, power transistors and other devices made from GaN process will be able to double their outputs with the new process.

The process, co-invented by electrical engineering professor Salah Bedair and materials science professor Nadia El-Masry, intentionally introduces voids into the GaN layer near its interface with a sapphire substrate. This causes thousands of defects typically present in the semiconductor material to be sucked into the voids.

The GaN film in the tests was around two microns thick with ellipsoidal voids around 0.25 micron in diameter, surrounded by a film with 1000 times fewer defects. Instead of degrading the performance of the film, the voids apparently enabled it to nearly double its output.

According to Bedair, the voids act as sinks for defects and dislocations near the interface, as well as acting as expansion joints for lattice mismatches. Bedair discovered the technique by chance when his graduate student, Pavel Frajtag, complained that nanowires had formed in bulk-grown GaN films formed using a maskless inductively coupled plasma/reactive ion etching technique. Bedair asked to try to eliminate the nanowires by using epitaxial overgrowth, which resulted in the void formation and dislocation trapping effect.


Currently the researchers are working on further characterisation of the material, as well as using the process to fabricate LEDs and other devices order to test its ability to boost the output of GaN devices.

 

Image: APL

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NCSU news itemAPL publication



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