3C-Silicon Carbide Photonics
Cubic silicon carbide (3C-SiC) combines the merits of other well known optical and quantum optical materials (e.g. Si, diamond, and III-V semiconductors such as GaP) in a single CMOS-compatible platform. The unique combination of material properties of 3C-SiC include: a wide band gap (2.4 eV), which is advantageous for generating optically-active and even room-temperature quantum emitters based upon impurities (color centers); planar device layer possessing a high index of refraction (2.55 at telecommunications wavelengths) and grown on a sacrificial substrate (Si), which enables strong optical confinement and strong light-matter interaction; and finally wide transparency range (0.54 – 2.00 μm) as well as strong second and third order nonlinear optical (χ(2) and χ(3)) properties, which is a prerequisite for broadband classical and quantum photonic frequency conversion.
Fig. 1. The process flow to generate suspended photonic crystal structures in 3C-SiC films. Process begins with 3C-SiC films grown on Si by the group of Gabriel Ferro (University of Lyon). The initial pattern transfer from resist into SiO2 (step d) is performed using CF4, CHF3, and Ar chemistry in a plasma etching system and a second pattern transfer from SiO2 into SiC (f) is done using HBr and Cl2. Final undercutting of the SiC device layer is achieved by isotropic etching of the underlying Si with a XeF2 vapor phase etcher (g).
Strong analogies may be made in motivating the development of a SiC nonlinear and quantum photonics platform to recent developments in wide band gap semiconductors, with SiC offering key material advantages. Compared to diamond, for example, electrical doping procedures and micro-fabrication recipes are readily available for SiC since it has been an important material in power electronics and microelectromechanical (MEMS) systems. Moreover, 3C-SiC photonic integration is facilitated by the ability to obtain high-quality and optically-thin (~200 nm) 3C-SiC films on a silicon substrate, thereby bypassing complex fabrication procedures such as Smart Cut, angled-etching, or deep-etching required in diamond and other hexagonal (e.g. 4H and 6H) bulk crystalline SiC phases. With recent and emerging demonstrations of ensembles of vacancy-related impurities in SiC offering electronic bound states (akin to the well-known Nitrogen-Vacancy center in diamond), their integration into photonic crystal cavities could potentially enable optical interconnects, such as low-power optical switches based on the cavity quantum electrodynamics (cQED), and could impact diverse areas from nanoscale sensors (electric field, magnetic field and temperature) in the biological/life sciences, to long-distance quantum networks. Finally, unlike Si and diamond, 3C-SiC is a non-centrosymmetric material and it possesses a non-zero χ(2) nonlinear frequency coefficient for fundamental and applied studies of cavity-enhanced nonlinear optics over a wide range of frequencies.
Figure 2. (a) L3 photonic crystal cavity fabricated in 3C-SiC. (b) FDTD simulation of the dominant (Ey) electric field component of the fundamental mode, with the outlines of the holes indicated. (c) Spectrum of a fundamental resonance. (d) Scaling of the fundamental resonance (Q ~ 1,000) with varying lattice constant across telecommunications wavelengths.
Figure 3. A variety of structures for integrated quantum and nonlinear photonics can be fabricated in 3C-SiC. (a) Photonic crystal waveguide for integration with cavities on-chip. Insets show device fabrication detail. (b) SEM micrograph of a crossbeam photonic crystal structure in 3C-SiC for cavity-enhanced nonlinear optics and cavity quantum electrodynamics.
We acknowledge Gabriel Ferro (University of Lyon) for providing 3C-SiC materials.
- M. Radulaski, T. M. Babinec, S. Buckley, A. Rundquist, J Provine, K. Alassaad, G. Ferro, J. Vučković, Photonic Crystal Cavities in Cubic Polytype Silicon Carbide Films, arXiv:1310.2222 (2013)
last modified on Thursday December 12, 2013