Integrated photonics on silicon with wide bandgap GaN semiconductor

Abstract

We report on GaN self-supported photonic structures consisting in freestanding waveguides coupled to photonic crystal waveguides and cavities operating in the near-infrared. GaN layers were grown on Si (111) by metal organic vapor phase epitaxy. E-beam lithography and dry etching techniques were employed to pattern the GaN layer and undercut the substrate. The combination of low-absorption in the infrared range and improved etching profiles results in cavities with quality factors as high as ∼5400. The compatibility with standard Si technology should enable the development of low cost photonic devices for optical communications combining wide-bandgap III-nitride semiconductors and silicon.

Efficient continuous-wave nonlinear frequency conversion in high-Q gallium nitride photonic crystal cavities on silicon

“…Additional enhancement can be introduced by high-Q cavities, such that nonlinearity is achieved with low photon count. Following the development of the GaN-on-Si platform 3 and further efforts that yielded improved figures for cavity Q-factors, 4 In this report, we present GaN slab PhC cavities on Si operating in the telecom range, with designs optimized for mode coupling and confinement. The characterization of fabricated cavities revealed record Q-factors, which has enabled enhanced second harmonic generation (SHG) and third harmonic generation (THG) by means of resonant far-field excitation.…”

“…Cavity Q-factors gradually dropped with increasing injector-hole radius, 13 down to a value of 2.7-4.4 × 10 4 for the largest considered injector sizes (∆r i = 8 nm and 10 nm for the L3 and H0 cavities, respectively). We have selected three injector sizes to be fabricated for each cavity (∆r i = [3,5,8] nm for the L3 cavity and ∆r i = [5,7,10] nm for the H0 cavity) to cover a coupling efficiency (η) range from approximately 2% to 20%. The PhC cell was chosen to be 65a by 39 √ 3a units in size, with the cavity residing at the center.…”

“…The grown gallium-face layer is c-axis oriented, with similar epitaxial properties to previous reports. 3 Fabrication of the PhCs was initiated by depositing a SiO 2 layer using plasma-enhanced chemical vapor deposition, to function as a hard etch mask. ZEP520A positive resist was spun on the SiO 2 layer, then patterned by a 100 keV electron beam (Vistec EBPG5000).…”

“…22 Amongst the relevant tensor elements of GaN 17 with regard to the cavity mode and crystallographic orientation, the ones with the principal contribution are χ (3) xxxx and χ (3) yyyy . For the L3 cavity shown earlier, the emission was fiber-coupled at the output port to a single-mode fiber and sent to a monochromator (600 lines/mm grating) with a cooled Si detector to monitor the intensity count.…”

“…While there is a clear trade-off theoretically between the coupling efficiency and Q-factor for a given cavity design, the upper limit on the Q-factor that is imposed by loss channels, given the disorder figure of current fabrication technology, makes room for introducing improved far-field coupling to enhance nonlinear processes without sacrificing the experimentally achievable light confinement. In contrast to commonly used semiconductors, the transparency of GaN for all participating frequencies of χ (2) and χ (3) processes enables the utilization of compact diode lasers as pumps. The platform's capability for integration and the fact that the demonstrated nonlinearity has been achieved under continuous-wave operation is promising for on-chip low-power applications, particularly integrated optical networks that can benefit from the generation of non-classical light states, frequency upconversion for improved near-IR detection, and all-optical switching to support emerging optical computing architectures.…”