Seminar/webinar F. Zwanenburg 'Silicon and Germanium Quantum electronics'

'Silicon and Germanium Quantum electronics'
Our research at the University of Twente focuses on spin and topological physics in silicon and germanium. We aim at controlling the spin states of individual electrons and holes with the ultimate goal of realizing single spin quantum bits as building blocks for future solid-state quantum computers. We make hybrid superconductor-semiconductor devices with Te and Ge nanowires for topological Josephson junctions. Ge/Si core/shell nanowires are suitable candidates for electrically driven spin qubits, and for the creation of Majorana fermions [1]. In highly tuneable hole quantum dots [2, 3], we observe shell filling of new orbitals and corresponding Pauli spin blockade [4]. In nanowires with superconducting Al leads we create a Josephson junction via proximity-induced superconductivity. A gate-tuneable supercurrent is observed with a maximum of ~60 nA [5]. We identify two different regimes: Cooper pair tunnelling via multiple subbands in the open regime the device [6], while near depletion the supercurrent is carried by single-particle levels of a quantum dot operating in the few-hole regime [5,7,8]. Secondly, we create ambipolar quantum dots in silicon nanoMOSFETs. We investigate the conformity of Al, Ti and Pd nanoscale gates by means of transmission electron microscopy [9]. We define low-disorder electron quantum dots with Pd gates [10], and depletion-mode hole quantum dots in undoped silicon [11]. The depletion-mode design avoids complex multilayer architectures requiring precision alignment and allows directly adopting best practices already developed for depletion dots in other material systems. Finally, we have realized ambipolar charge sensing by fabricati a single-electron transistor next to a single-hole transistor. Using active charge sensing the single-electron transistor can detect the few-charge renggime in the hole quantum dot [12].

[1] C. Kloeffel et al., Phys. Rev. B 84, 195314 (2011). [2] M. Brauns et al., Applied Physics Letters 109, p. 143113 (2016). [3] F. Froning et al., Applied Physics Letters 113, p. 073102 (2018). [4] M. Brauns et al., Phys. Rev. B 94, 041441(R) (2016). [5] J. Ridderbos et al., Advanced Materials, 1802257, (2018). [6] J. Xiang et al., Nature Nanotechnology 1, 3 (2006). [7] J. Ridderbos et al., Physical Review Materials, 3, 084803 (2019). [8] J. Ridderbos et al., Nano Letters 20, 1, p. 122 (2020). [9] P. C. Spruijtenburg et al., Nanotechnology, (2018). [10] M. Brauns et al., Scientific Reports 8, 5690, (2018). [11] S. V. Amitonov et al., Applied Physics Letters 112, p. 023102 (2018). [12] A. J. Sousa de Almeida et al., Phys. Rev. B 101, 201301(R) (2020).