Monolithic LEDs tunable from 460 to 650nm
One step in that direction comes in the shape of monolithically integrated full colour LED arrays, where each individual LED can be driven to output just any colour including a full white mix. This is no small feat in the world of LED design was achieved by researchers at Ostendo Technologies and was the topic of a recent publication in AIP Advances under the title “Growth of monolithic full-color GaN-based LED with intermediate carrier blocking layers”.
In this paper, lead author Dr. Hussein S. El-Ghoroury who also happens to be Ostendo Technologies’ Founder and CEO shares a novel tricolour InGaN-based LED design obtained through a common metal-organic chemical deposition (MOCVD) process.
His team relied on specially designed intermediate carrier blocking layers (ICBLs) to control the carrier injection distribution across the active regions of multiple quantum wells stacked one upon another, effectively guiding the majority of carriers into the designed quantum wells so they would recombine and generate light at the QW’s specific wavelengths depending on the current-densities running throughout the device.
The monolithic InGaN-based LED they designed is able to achieve three primary colours of light from one device at selected current densities, starting at 650nm and then decreasing to 460nm or lower as the injection current increases.
The epitaxial structures of these monolithic LEDs were grown on c-plane (0001) sapphire substrates and in the MQW active region, a variety of AlGaN-based alloy layers were incorporated to control carrier distribution as well as improving material quality. The ICBL between the blue and green wells was composed of 10nm Al0.07Ga0.93N sandwiched between 5nm GaN layers. The ICBL between the green and red wells was composed of 10nm Al0.20Ga0.80N sandwiched between 5nm GaN layers.
Under varying injection currents the light emission changed from red (650nm) to green (530nm) and then to blue (460nm) at 15, 200 and 400mA, respectively.
blue) from a tricolour LED wafer.
At low currents (around 5mA), the device first emits a red light and then the colour shifts to amber, yellow, green and blue as currents are increased. All colours can be combined and mixed by using different combinations of current pulse intensity and width, write the researchers in their paper and Ostendo Technologies is now busy refining such colour mixing techniques to achieve other colours, including white light, with correlated colour temperature across adjacent different pixels.
Visit Ostendo Technologies at www.ostendo.com
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