Researchers at Kansas State University (Manhattan, KS) have reported successful growth of high-quality crack-free gallium nitride (GaN) epilayers on 6-in.-diameter silicon (Si) substrates using metal-organic chemical-vapor deposition to fabricate blue-emitting nitride multiple-quantum-well light-emitting diodes (LEDs). Previously demonstrated nitride growth on Si substrates has been limited to 2 in. for photonic structures and 4 in. for heterojunction field-effect transistors.

For the growth of nitride materials on large-area Si substrates, however, problems associated with cracks and bowing can be severe because of the increased difficulty of maintaining temperature uniformity and mechanical strength over a larger area. The relatively small lattice constant of an aluminum nitride nucleation layer can serve to counterbalance the thermally induced tensile strains by inducing compressive strain on subsequent GaN layers, according to previous studies, thereby supporting the growth of crack-free and relatively thick GaN layers. The Kansas State team has exploited this potential to fabricate 492 nm blue LEDs on a silicon substrate and achieved an optical-power output of about 0.35 mW at 20 mA, measured from the top surface of unpackaged LED chips. Contact Hongxing Jiang at jiang@phys.ksu.edu.