11 September 2020
Green and orange LEDs on porous GaN
University of California Santa Barbara (UCSB) in the USA has been using a gallium nitride porosification process to increase the wavelength of indium gallium nitride (InGaN) micron-scale light-emitting diodes (μLEDs) [Shubhra S. Pasayat et al, Appl. Phys. Lett., vol117, p061105, 2020]. The porous GaN is less rigid, allowing overlying InGaN ‘pseudo-substrate’ (PS) layers to be less strained.
The relaxed InGaN in turn increases indium uptake during regrowth processes through the ‘composition pulling effect’, creating higher-indium-content layers and hence longer emission wavelengths. Composition pulling is ascribed to the reduced lattice mismatch between the InGaN growth front and the underlying InGaN pseudo-substrate, compared with InGaN grown directly on GaN. The work resulted in green (500-565nm)- and even orange (590-625nm)-emitting devices.
The researchers see the potential for applications from near-eye head-mounted to large-area self-emitting displays. Also, smaller device sizes often allow for faster switching speeds for GHz-level modulation bandwidth in visible light communications (VLC). “Owing to their small form factors, μLEDs are also being considered to possess immense potential in medical applications and mask-free lithography,” the team adds.
The UCSB group has also recently reported on use of the same concept for producing high-aluminium-content AlGaN pseudo-substrate films, which may lead to better-performing very-short-wavelength deep-ultraviolet-emitting devices [Shubhra S. Pasayat et al, Appl. Phys. Lett., vol117, p062102, 2020].
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