Low-Droop LED Structure on GaN Semi-polar Substrates

Brief Description

An LED structure of GaN thin films grown by metal organic chemical vapor deposition (MOCVD) on (20-2-1) semi-polar GaN substrates that demonstrate low efficiency droop.

Background

When III-nitride-based LEDs are grown on nonpolar and semi-polar planes, unbalanced in-plane biaxial strain causes the curvature of the highest valence band to increase. The result is an increase in symmetry between the valence band and conduction band curvatures. For wide bandgap materials, symmetric conduction and valence bands may suppress Auger recombination, which is the mechanism widely accepted as being responsible for efficiency droop. Particularly in high indium composition layers, it has been observed that quantum wells grown on certain semi-polar planes may have superior alloy uniformity to devices grown on c-plane; this difference should lead to reduced alloy scattering and the devices should demonstrate reduced efficiency droop in general. 

Description

Researchers at UC Santa Barbara have developed an LED structure of GaN thin films grown by metal organic chemical vapor deposition (MOCVD) on (20-2-1) semi-polar GaN substrates that demonstrate low efficiency droop. These devices provide a pathway to nitride-based devices that are free from the droop effect. The structure incorporates n-type superlattice layers located below the quantum wells (QW), a QW active region of at least three periods, and p-type superlattice layers above the QWs. Devices grown on the (20-2-1) plane have shown that they have superior alloy uniformity, reduced alloy scattering, and thus diminished efficiency droop. 

Advantages

·         Superior alloy uniformity

·         Greatly reduced alloy scattering

·         Reduced efficiency droop 

Applications

·         Solid state lighting systems

Patent Status