Grating-assisted resonant-cavity LEDs: toward thin film devices for heterogeneous integration

Design and fabrication of thin film GaAs Grating-Assisted Resonant-Cavity LEDs (GA-RCLED) emitting at 980 nm are reported. The devices are fabricated by gluing the sample and a transfer substrate with benzocyclobutene (BCB) and consequently thinning the sample. The design is optimised for a high extraction efficiency. The efficiency of substrate emitting planar RCLEDs is limited by leaky DBR modes. This quasi continuum of modes does not fall in the DBR stop band and is internally reflected at the semiconductor-air interface. Consequently, the leaky modes are absorbed in the substrate and are lost. The use of a thin film device can avoid this loss term. The laterally propagating mode can be recuperated by the use of a grating. The diffractive properties of the periodic grating can redirect the resonant guided mode to the extraction cone. The 2-D grating is defined on the surface of the thin film RCLED by means of holographic exposure. As the devices are thinned they are more compatible with wafer scale integration with electronic devices.