Fabrication of dual-gated devices on undoped Si/SiGe heterostructures*

Undoped accumulation mode Si/SiGe heterostructures have recently emerged as a promising platform for the fabrication of few-electron silicon spin qubits. Spin blockade has been observed in an accumulation mode double dot [1] and a record mobility of 1.6 million cm$^2$/(Vs) has been achieved in undoped wafers grown at National Taiwan University [2]. We develop a fabrication process for dual-gated accumulation mode structures and form a stable two-dimensional electron gas by applying positive bias to a global top gate. The resulting 2DEG has charge densities of $2-5\times10^{11}$/cm$^{2}$ and mobilities up to 200,000 cm$^2$/(Vs). We present preliminary data from quantum point contacts fabricated in this geometry. \\ References:\\ \noindent [1] M. G. Borselli \textit{et al.}, Appl. Phys. Lett. {\bf99}, 063109 (2011).\\ \noindent [2] T. M. Lu \textit{et al.}, Appl. Phys. Lett. {\bf94}, 182102 (2009).\\