Soraa Inc of Fremont, CA, USA, which develops solid-state lighting technology built on ‘GaN on GaN’ (gallium nitride on gallium nitride) substrates, has received an award from the US Department of Energy for its work in the development of high-efficiency m-plane LEDs grown on low-defect density bulk GaN substrates. The firm demonstrated a very high peak internal quantum efficiency (IQE of 88%), low efficiency droop (10% from 10A/cm2 to 100A/cm2) and perfect wavelength stability (up to 200A/cm2) at a wavelength of 450nm LEDs.
“Research and development of LEDs on bulk GaN substrates is one of the critical approaches to the technological development of Solid State Lighting — a sentiment recently echoed by the National Academy of Sciences,” says Jim Brodrick, manager of the US Department of Energy’s Solid State Lighting Program. “We are pleased to recognize Soraa's pioneering work in this area,” he adds.
Soraa reckons that its GaN-on-GaN LEDs handle more current and emit substantially more light (about ten times) per area of LED wafer material than the conventional approach of depositing GaN layers on cheaper foreign substrates such as sapphire, silicon carbide (SiC) or silicon. Its GaN-on-GaN technology leverages the advantages of the native substrate, including lower crystal defect densities (by more than a 1000 times), that allow reliable operation at very high current densities (the same principle that enabled Blu-ray laser diodes). Also, the native substrate advantages of optical transparency and high electrical and thermal conductivities enable a very robust, simple LED design for maximum performance. Another advantage of GaN-on-GaN is the flexible choice of crystal growth plane, which has demonstrated advantages in high peak IQE and low-droop LED performance.
