Integrated high reflectivity silicon substrates for GaN LEDs



Growth of GaN on epitaxial distributed Bragg reflectors (DBR) capable of 80% reflectivity at typical III-N based LED operating wavelengths is presented. Such structures are formed by growing single crystal multilayers of gadolinium oxide-silicon stacks on silicon (111) substrates. The large refractive index difference between gadolinium oxide and silicon (Δn = 2.2) allows highly reflective DBR mirrors to be achieved at as little as three periods. Growth of GaN is demonstrated on the DBR mirrors making these structures suitable for GaN based LED growth. DBR mirrors embedded in this engineered substrate act as a reflecting mirror for incident light from a LED grown on top of this substrate. This potentially allows increased light extraction and higher output power from these LEDs compared to that of similar LEDs grown on silicon substrates. Performance of DBR mirrors with GaN top layers as a function of the incident angle of a 488 nm laser is investigated. X-ray diffraction and TEM are used for structural characterization of these grown structures. This engineered substrate, Mirrored SiliconTM, is suitable for high volume manufacturing at 150 and 200 mm wafers sizes. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)