At the 2006 IEEE International Electron Devices Meeting (San Francisco, CA) last December, researchers from Matsushita Electric (Osaka, Japan) and the Nagoya Institute of Technology (Nagoya, Japan) described highly efficient gallium nitride (GaN)-based light-emitting diodes (LEDs) fabricated on silicon (Si) substrates. In the first half of a flip-chip growth process, the researchers formed a 2-D photonic-crystal pattern on a seed Si substrate prior to epitaxial growth of an aluminum nitride (AlN) and GaN/AlN multilayer buffer, followed by InGaN multiple-quantum-well (MQW) active layers and a reflective p-type electrode on the surface. The device was then flipped over and bonded onto a thermally conductive Si substrate. The seed Si substrate was removed, leaving a replication of the photonic-crystal pattern in the multilayer buffer.
The resulting LED achieved a 70% improvement in luminous intensity over LEDs grown without the patterning process due to the replicated photonic crystal. Moreover, the growth on patterning led to periodic reductions in dislocation density between the multilayer buffer and MQW layers along the sidewalls of the photonic-crystal pattern. The ability to use relatively inexpensive Si substrates is expected to cut manufacturing costs of GaN-based LEDs. Contact Kenji Orita at [email protected].