Advanced epiready template on silicon for low-defect-density GaN thin film – EASY-GaN

The EASY-GaN project proposes to develop an advanced epiready substrate to produce thin (< 2 micromètre), high-quality (threading dislocation density < 5x10E8 cm-2) GaN layers on silicon substrates. This product allows addressing the challenging issue of fabricating low-cost GaN-based LEDs on silicon substrates for lighting. Indeed, fabricating high-quality GaN epilayers on large and low-cost silicon substrates in a very short time epitaxial run, a strong reduction of the cost of LEDs is expected compared to those fabricated on sapphire. Moreover, the advanced substrate is said “epiready” because it could be used by epitaxial growers as it is, that is to say that with no special attention to the fact that it is mainly a silicon substrate. This aspect is particularly important because it would allow companies well established in the field of GaN-based devices, as well as new comers potentially interested to come into this business, to easily access the technology of GaN on Si. From a technical point of view, the advanced epiready substrate relies on a specific surface treatment (patent pending) of an AlN buffer layer epitaxially grown on a silicon substrate. This surface treatment allows growing GaN in a 3D growth mode reducing efficiently the threading dislocation density. Actually the reduction of the dislocation density is even stronger than the one observed for other surface treatments usually used. Also, the surface treatment allows coalescing more rapidly than usual which allows fabricating device-quality GaN layers thinner than usual. Last but not least, it allows to passivate the surface of AlN buffer layers preventing any oxidation reaction under air exposure. This aspect allows to store and to maintain the remarkable properties of the advanced epiready substrate along the time. Finally, the advanced epiready substrate on which is based the present project, is a silicon substrate overgrown by an epitaxial AlN buffer layer terminated by a specific surface treatment. The objectives of the EASY-GaN project are to strengthen the original product, to acquire a strong intellectual propriety and to assess the best development strategy possible.