Silicon Carbide (SiC) is a wide-bandgap semiconductor already widely used for electronic and photonic devices, and hosts a number of color centers. The negatively charged silicon monovacancy centers (VSi−) and divacancies (VSiVC) in the polytype 4H-SiC are optically active point defects with long spin coherence times and potential applications in quantum information science. Nanobeam photonic crystal cavities (PCC) allow emission enhancement to improve otherwise low count rates and collection efficiency. Additionally, these defects emit in the near-infrared range, which could allow for easier integration into telecommunications systems. Our group focuses on making use of the emitters to couple them to photonic cavities to enhance their spin-photon interactions in order to better study the fundementals of semiconductor defect systems ( charge state, strain, and diffusion.
Figure: Depiction of 4H-SiC crystal lattice. When a single silicon atom is removed from the lattice, the collection of electrons left at this site luminesce brightly though a directly electronic transition (V1/V1'/V2) or through the phonon side-band (PSB).
Silicon carbide (like other semiconductors) can be photo-electrochemically etched in a way that is dopant selective, giving the flexibility to use robust wet etching processes to form undercut optical structures, including nanophotonic cavities with high quality factor and sub-wavelength mode volumes. We have shown that these cavities can be used to readily enhance the photon transition rate of spins in silicon carbide by 75x. In addition we have also shown the cavities to be flexible "nano-scopes" of the charge state dynamics and diffusive motion of defects in an ultra-small volume.
Figures (left to right): Fig1(a-c) High Q photonic crystal cavity (PCC) fabricated in 4H SiC. Fig2(a-d) Gas tuning of PCC mode into resonance with V1/V1' defect transitions. Fig3(a) Real time monitoring of above band-gap induced defect motion monitored via the PCC.
References (see Publications):
- Enhanced cavity coupling to silicon vacancies in 4H silicon carbide using laser irradiation and thermal annealing
- Energetics and kinetics of vacancy defects in 4H-SiC
- Selective Purcell enhancement of two closely linked zero-phonon transitions of a silicon carbide color center
- Fabrication of High-Q Nanobeam Photonic Crystals in Epitaxially Grown 4H-SiC
Diamond is a material host of more than 100 different color centers. Of particular interest is the Nitrogen-Vacancy (NV) defect, where nitrogen substitutes a carbon atom and lies next to a vacancy site in the diamond lattice. This defect luminesces in the visible regime, its spin state can be optically read out and initialized, and it can also be coherently manipulated, which makes it a leading candidate for solid-state quantum information processing . Our group focuses on changing the material properties, such as the structure of the diamond, to enhance the emission properties and manipulate these defect properties.
We have developed a process to fabricate high quality single-crystal diamond membranes. Diamond membranes are lifted off from an ion implanted bulk diamond sample using an aqueous electrochemical etching process . A high quality diamond thin film is grown on top of the lifted-off membranes . The diamond membranes are then mechanically stamped onto a dielectric substrate and the lifted-off membranes are etched using an inductively coupled plasma- reactive ion etching (ICP-RIE) process leaving the high quality overgrown diamond membranes on top of a dielectric substrate. Optical micro-cavities and photonic crystal cavities can be subsequently fabricated on the high quality diamond membranes [4, 5].
In addition, we characterize and study the chemistry of diamond surfaces. In particular, we're interested in understanding how to manipulate shallow NV properties, such as charge and lifetime, with surface chemistry. We functionalize the surface of bulk and nanodiamonds with biomolecules and organic ligands, for applications in biotagging and spin sensing.
Nanofabrication of photonic devices
To better study properties of the defect centers in diamond, we pattern optical micro-cavities on our single crystal diamond membranes. Using both photolithography and electron beam lithography, we have patterned microdisks, micro-ring resonators, and both one- and two-dimensional photonic crystals. We study the coupling of defect emission to our optical cavities. Such coupling allows for resonant enhancement of the defect emission, an effect which we can observe using photoluminescence spectroscopy.
- Awschalom, D. D., Bassett, L. C., Dzurak, A. S., Hu, E. L. & Petta, J. R. Quantum Spintronics: Engineering and Manipulating Atom-Like Spins in Semiconductors. Science 339, 1174–1179 (2013).
- Magyar, A. P. et al. Fabrication of thin, luminescent, single-crystal diamond membranes. Appl. Phys. Lett. 99, 081913–081913–3 (2011).
- Aharonovich, I. et al. Homoepitaxial Growth of Single Crystal Diamond Membranes for Quantum Information Processing. Advanced Materials 24, OP54–OP59 (2012)
- Lee, J. C., Magyar, A. P., Bracher, D. O., Aharonovich, I. & Hu, E. L. Fabrication of thin diamond membranes for photonic applications. Diamond and Related Materials 33, 45–48 (2013).
- Lee, J. C., Aharononvich, I., Magyar, A. P., Rol, F. & Hu, E. L. Coupling of silicon-vacancy centers to a single crystal diamond cavity. Optics Express 20, 8891–8897 (2012).
- Koehl, William F., et al. "Room temperature coherent control of defect spin qubits in silicon carbide." Nature 479.7371 (2011): 84-87.