Event

 

Name: Infiter Tathfif

 

Committee:

Professor Ronald L Walsworth (Chair)

Professor Thomas E. Murphy

Professor Saikat Guha

Date/time: May 26, 3 PM - 4 PM

 

Location: AVW 2460

 

Title: QUANTUM SILICON CARBIDE MICROSCOPE BASED ON V2 COLOR CENTERS IN 4H-SiC

 

Abstract: Mapping microscopic fields influencing quantum materials and devices at low temperatures is of significant interest in condensed matter physics. Wide-field imaging with color centers, such as nitrogen-vacancy (NV) centers in diamonds, is becoming a commonly used technique to characterize local magnetic fields for its speed, maturity, and simplicity. However, difficulty in obtaining high-quality, thin NV layers with low inhomogeneity, limitations on sample sizes, and the high price of diamond films prompt researchers to seek alternative options. The V2 silicon vacancy defect in 4H-SiC can be a potential substitute for NV centers for its comparable optical and spin properties. Additionally, SiC offers industry-standard CMOS integration and can be purchased in bulk for its commercial availability. However, the dipole orientation of the V2 center and high index of refraction result in poor collection efficiency for 4H-SiC, requiring the fabrication of micro and nanostructures in the sample. In addition, the low ODMR contrast (<1% at room temperature) degrades sensitivity.

 

To improve the readout contrast, we first explore resonant optical excitation of V2 ensembles at cryogenic temperatures and compare the results with the off-resonant case. We report a maximum ODMR contrast of 50% with only 2 µW of resonant laser power, almost 100 times improvement over off-resonant excitation in a HPSI 4H-SiC sample. We attribute this high readout contrast to a subset of V2 centers that have one spin-selective optical transition resonant with the laser and present an optical pumping mechanism to explain the phenomenon. Next, we employ this resonant excitation technique on etched nanopillars on a 1 µm thin epilayer of 4H-SiC. Preliminary results show orders of magnitude improvement in resonant optical excitation efficiency compared to bulk SiC at ~4 K. Further, we demonstrate early attempts at camera-based ODMR and achieve a high readout contrast across all the pixels. Moreover, the nanopillars require only 10 mW/mm² of resonant excitation laser.

Thus, leveraging improved photon collection, reduced laser power, and enhanced readout contrast, our efforts lay the foundation for a cryogenic wide-field imager with V2 centers in 4H-SiC. Future work will primarily focus on the implementation of this SiC microscope and improving the magnetic sensitivity. Additional gains in sensitivity can be achieved by using isotopically purified samples and installing a phase modulator to comb the laser frequency and access more of the defect ensemble, boosting the signal-to-noise ratio. Further, we aim to demonstrate the capabilities of this cryogenic wide-field imager by imaging vortices in superconductors. In superconducting electronics, pinpointing the locations of these disruptive vortices is of utmost importance for mitigating their effects. The proposed SiC microscope will have the potential to image the associated local magnetic fields in near real time, contrary to the traditional scanning method, and help us effectively implement mitigation strategies.