Nonpolar and semipolar GaN LEDs show great improvement

Record performance figures for nonpolar and semipolar LEDs have been reported by researchers at the Solid State Lighting & Display Center (SSLDC) at UC Santa Barbara (UCSB), and the Japan Science & Technology Agency’s Exploratory Research for Advanced Technology program (JST ERATO), according to LEDs magazine.

Nonpolar and semipolar LEDs are a new class of gallium nitride (GaN) based devices based on non-standard GaN material orientations. Compared with conventional GaN-based LEDs, the nonpolar and semipolar versions are expected to exhibit higher external quantum efficiency (EQE) at high current densities, as well as emitting polarized light.

The new non-polar LEDs have an external quantum efficiency of 41% and radiant powers as high as 25 mW for standard size (300 x 300 µm) and operating current (20 mA).

Semipolar LEDs of the same size exhibited external quantum efficiency of 30% and radiant powers as high as 18 mW, also at 20 mA.

The UCSB groups have also reported conventional c-plane LEDs with EQE of 66% and 35 mW radiant power. These LEDs have been used to make white LED lamps which boast a luminous efficacy of 116 lm/W.

While high efficiency is desirable in many applications, the polarized emission is also likely to prove important. 'The nearest term application [for these devices] is LCD backlighting using polarized light from non-polar LEDs,' says DenBaars.

Research funding was provided by JST ERATO and also by SSLDC, which is focused on advancing new semiconductor-based energy efficient lighting and display technologies through partnerships with industry leaders.