Industrial production of GaN and InGaN-light emitting diodes on SiC-substrates

Blue light emitting diodes (LEDs) based on GaN or InGaN have a large market , e.g. for communication, industry and automotive applications. Since 1998, OSRAM Opto Semiconductors has been producing blue LEDs on a large scale, c oncentrating on the automotive market. LEDs in the wavelength range 450-480 nm are grown by metalorganic vapour phase epitaxy (MOVPE) on SiC. This sub strate material offers many advantages from the epitaxial and device proces sing points of view. To fulfil the strong consumer recommendations not only do the epitaxial processes have to be developed, but also improvements in chip technology and package design help to stabilise electrical and optical properties on these high level demands. For example, low forward voltages, high light output powers at 20 mA, low reverse currents, long term stabili ty and high electrostatic discharge robustness have to be guaranteed in a t emperature range of -55-+85 degreesC and at a maximum humidity of 85%. Elec trical and optical parameters were tested on every produced chip not only t o remove LEDs before packaging, which do not meet the specifications, but t o control and optimise the applied technological steps. As an example we de monstrate a testing method for controlling the process and optimising the p -contact. Optimisation of n- and p-contact as well as the improvement of ep itaxy helped to increase the light output power from 1 mW in 1998 to more t han 6 mW at present when mounted in a 5 mm radial lamp. All electrical para meters of these high brightness LEDs could also be improved or at least kep t in the demanded specification range. (C) 2001 Elsevier Science B.V. All r ights reserved.