Progress of InGaN Light Emitting Diodes on SiC

Abstract

We present brightness improvements of blue InGaN chips on SiC substrates. Chip shape, performance of the contacts, high structural quality of the InGaN quantum well layers are essential for an optical output as high as 9.5 mW at 470 nm and 20 mA. The external quantum efficiency is 18%. The light extraction out of the chip is increased to 55% as calculated by a ray trace simulation. This is the highest value ever reported on InGaN chips, which are conventionally mounted with epitaxial layers upside. The optimized chip side walls have vertical angles of 60°. The reflectivity at the p-contact is increased to 90% for flat angles of 0 to 20°. An internal quantum efficiency of 32% is estimated from the values of light extraction and external quantum efficiency. The epitaxial layers are improved by optimizing the growth parameters of the quantum wells interfaces. Electrical losses are reduced by better interface quality of epitaxial layers and by an improved p-contact resistance of 10—4 Ω cm2, respectively.