ABSTRACT
Microdisks fabricated with III-nitride materials grown on GaN substrates are demonstrated, taking advantage of the high material quality of homoepitaxial films and advanced micro-fabrication processes. The epitaxial structure consists of InGaN/GaN multi-quantum wells (MQWs) sandwiched between AlGaN/GaN and InAlN/GaN superlattices as cladding layers for optical confinement. Due to lattice-matched growth with low dislocations, an internal quantum efficiency of â¼40% is attained, while the sidewalls of the etched 8 µm-diameter microdisks patterned by microsphere lithography are optically smooth to promote the formation of whispering-gallery modes (WGMs) within the circular optical cavities. Optically pumped lasing with low threshold of â¼5.2 mJ/cm2 and quality (Q) factor of â¼3000 at the dominant lasing wavelength of 436.8 nm has been observed. The microdisks also support electroluminescent operation, demonstrating WGMs consistent with the photoluminescence spectra and with finite-difference time-domain (FDTD) simulations.
ABSTRACT
Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440 mW/cm2 output power density at 20 mA from such microrings with diameters of 30 to 50 µm. The first steps towards achieving an integrated photonic circuit are demonstrated.
