Stabilizing lateral strained-Si/SiGe material quantum dots

In enhancement-mode SiGe quantum dot structures [2], 2DEG electrons are generated via the application of a positive global gate. The carrier mobility in such structures is limited by disorder potential at the oxide/silicon interface. Recently it was shown that the deteriorating effect of charge fluctuations can be substantially mitigated by incorporating a shielding electron layer at the surface -- a thin Si quantum well cap layer [1,2]. This cap layer can, however, cause instabilities, drifts and hysteretic behaviour. In this work we study the stability of a tunable quantum dot defined by lateral gates in a Si/SiGe structure with a thin silicon cap layer and Si3N4 dielectric layer between the global gate and the structure [2]. Different ``stabilization'' procedures are explored to stabilise the device using both dc transport and charge sensing measurements at 300 mK.~ \\[4pt] [1] T. M. Lu, et al., Applied Physics Letters \textbf{99} (2011)\\[0pt] [2] C.-T. Huang, J.-Y. Li, K. S. Chou, and J. C. Sturm, Applied Physics Letters \textbf{104} (2014)