Characterization of enhancement-mode two-channel triple quantum dot device fabricated from an undoped Si/Si$_{\mathrm{0.8}}$Ge$_{\mathrm{0.2}}$ quantum well hetero-structure.

Recently, single- and double-dot characteristics of an enhancement-mode quantum dot device fabricated from an undoped Si/Si$_{\mathrm{0.8}}$Ge$_{\mathrm{0.2}}$ hetero-structure were reported in [1]. As compared to Si/SiGe hetero-structures with a Ge concentration of 30{\%} typically encountered, a 20{\%} Ge concentration offers high electron mobility, and the fabrication process flow is simplified to incorporate a single accumulation metal-gate layer. We report a number of new results for the device which consists of two channels (upper and lower) formed with two separate accumulation gates. With other gates, a double-dot (in upper channel) and single-dot (in lower channel) can be formed under the accumulation gates energized positively. We demonstrate charge sensing of the upper double-dot with the lower single-dot. We also discuss the formation of a triple-dot formed by coupling the single-dot in the lower channel when made non-conducting to the double-dot in the upper conducting channel. We will discuss technological issues, and describe an intriguing and reproducible phenomenon in the quantum dot behavior that occurs at a temperature \textasciitilde 1 K during the $^{\mathrm{3}}$He cryostat refresh cycle. [1] T. M. Lu \textit{et al}., Appl. Phys. Lett. \textbf{109}, 093102 (2016).