LEDs grown on semi-polar InGaN emit green and amber colors
Long wavelength emitters such as green/yellow are not only important for the fabrication of solid-state lighting with ultra energy efficiency but also crucial for increasingly demanding opto-genetics applications (especially yellow emitters). The LEDs were grown on an overgrown semipolar (11-22) GaN on micro-rod array templates, which were fabricated on GaN grown on m-plane sapphire.
Compared to commercial LEDs grown on the c-Plane, the research team’s green LEDs grown on the semipolar material showed reduced blue-shift in the emission wavelength with increasing driving current. The same observations were made in blue-shifts for the yellow-green and yellow LEDs, which the researchers noted suggested an effective suppression in quantum confined Star effect in their LEDs.
Electroluminescence emission photos of (a) green, (b) yellow-green, (c) yellow, and (d) amber LEDs, taken at 5, 20, and 100mA. (Photo courtesy of Applied Physics Letter)
On-wafer measurements yielded a linear increase in the light output with the current, and external quantum efficiency demonstrated a significant improvement in the efficiency-droop compared to commercial c-plane LED. Electro-luminescence polarization measurements showed a polarization ratio of about 25% in the semipolar LEDs.
The researchers claim the preliminary results suggest that the overgrowth technology is a potentially cost-effective approach to achieving semipolar GaN emitters with high performance in a long wavelength region. For more, see the study published in the journal Applied Physics Letters: "(11-22) semipolar InGaN emitters from green to amber on overgrown GaN on micro-rod templates."