GaN/mirror/Si light-emitting diodes for vertical current injection by laser lift-off and wafer bonding techniques

A p-side-up GaN/mirror/Si light-emitting diode (LED) for vertical current injection has been fabricated by laser lift-off and wafer bonding techniques. A variety of metallic mirrors (Au, Al, and Ag) were chosen to improve the optical reflectivity and contact resistance with n-GaN. The GaN/mirror/Si LED with a silver mirror achieved a maximum luminance intensity of 45mcd (20 mA) with a low forward voltage of 3.5V. This luminance intensity is over two times that of the original planar GaN/sapphire LED. Under high current injection, the GaN/mirror(Ag)/Si LED also showed a more stable emission wavelength than the planar GaN/sapphire LED. This can be explained by the fact that the Si substrate provides a good heat sink and alleviates the joule heating problem. On the basis of these results, the p-side-up structure confirms the possibility of the simultaneous realization of a lower contact resistance and higher reflectivity for GaN/mirror/Si LEDs.