In 1994, Nichia Corporation of Japan broke through the key technology of nucleation growth of GaN materials. Soon, P-type GaN was realized by annealing technology, and then GaN LED was successfully developed. In recent years, through the enhancement of epitaxial technology, the internal quantum efficiency of GaN LED has been greatly improved. Combined with the techniques of improving the light output efficiency such as roughening, flip-chip, and PSS substrate, GaN-based LED has been widely used in full-color display and traffic signal lights. In the fields of automotive lamps, LCD backlights, indoor lighting and street lighting, semiconductor lighting has matured and entered thousands of households.
At present, most of the GaN-based LEDs are prepared using a relatively inexpensive sapphire as a substrate material. However, sapphire substrates have a lattice mismatch of up to 17% with GaN materials. Such large lattice mismatches result in high dislocation densities, resulting in an increase in non-radiative recombination centers in GaN LEDs, limiting Further improvement in quantum efficiency. The lattice fit of SiC substrate to GaN material is only 3%, which is much smaller than the lattice fit between sapphire substrate and GaN material, so the GaN material epitaxially grown on SiC substrate will have less dislocation density. The crystal quality will be higher, and the thermal conductivity (4.2W/cm.K) of SiC is much larger than that of sapphire, which is beneficial to the device operating at high current.
Fig.1 X-Ray half-width result of epitaxial GaN on SiC substrate
However, the preparation of SiC substrates is difficult, and the nucleation of epitaxially grown GaN is also difficult. Therefore, the technology for preparing GaN LEDs on SiC substrates is limited to a small number of companies that master SiC substrate preparation technology represented by CREE in the United States. At present, the GaN LED produced by Cree in the United States is packaged in white light, and the lumen efficiency has exceeded 200 lm/W, far exceeding that of other peer manufacturers.
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