Robust Fabrication Techniques for Si/SiGe Quantum Dots

Si/SiGe quantum dots promise a long spin coherence time due to reduced electron-nuclear spin interaction. Nevertheless, successful device yield has been limited in this novel material system due to difficulties in producing reliable ohmic contacts and Schottky gates. We have successfully developed fabrication processes that produce robust ohmic contacts and non-leaky Schottky gates. The ohmic contacts typically have a two-probe resistance of a few tens of kiloohms and the Schottky gates have no detectable leakage current up to an applied voltage of -5 V. In typical devices we are able to pinch off the quantum point contacts with a voltage range between -1.5 V to -4.5 V. Recent experimental results will be discussed. This work was supported by the NSF under Grant No. DMR-0804488, by the NSA, LPS and ARO under Agreement No. W911NF-04-1-0389, and by the ARO under Agreements No. W911NF-06-1-0312 and No. W911NF-06-01-0361.