Wuhan team grows high-quality AlN films on sapphire
Dislocation filtering and strain relief achieved by deliberately introducing voids during the growth process
Researchers from Wuhan University in China have reported a solution to the growth of high-quality AlN films on sapphire substrate. They deliberately designed a growth modification process to introduce voids into the AlN films for dislocation filtering and strain relief, which they say has produced almost stress-free AlN films on a flat sapphire substrate.They published the results in Applied Surface Science.
AlGaN based LEDs that emit light in the UVC spectral range are attracting increasing attention, not least due to their potential for use in disinfection during the ongoing COVID-19 pandemic. “The realising of high-quality AlN films on cost-efficient substrate is the main challenge in pursuing commercially available high-efficiency AlGaN based UVC LEDs,” said Shengjun Zhou. “We put forward a cost-efficient strategy, which enables the growth of high-quality AlN films on flat sapphire substrate”
Generally, AlN films grown on sapphire substrates suffer from poor crystal quality and high residual stress due to the large mismatch in lattice constants and thermal expansion coefficients between AlN and sapphire. The researchers demonstrated that deliberately introduced voids significantly reduced underlying dislocations by inducing voids termination at the void-sidewalls. Furthermore, as an additional stress relief channel, the voids not only reduced the risk of cracking during growth but also reduced compression stress after cooldown, resulting in a nearly stress-free AlN film on the flat sapphire substrate.
“In comparison with the strategy of epitaxial lateral overgrowth on patterned substrates, which generated voids through costly photolithography and dry etching steps, our strategy is much more simple and cost-efficient,” said Zhou. “We believe that this strategy hold great promise for the commercialisation of AlGaN based UVC LED.”
'Growth of high-quality AlN films on sapphire substrate by introducing voids through growth-mode modification' by Bin Tang et al; Applied Surface Science, Vol. 518, 146218 (2020).