Spin-polarized edge states of quantum Hall systems on silicon basis Carsten Kentsch * , Wolfgang Henschel, David Wharam, Dieter P. Kern Institut fu ¨ r Angewandte Physik, Universita ¨t Tu ¨ bingen, Auf der Morgenstelle 10, 72076 Tu ¨ bingen, Germany Available online 21 February 2006 Abstract In the context of quantum computing in silicon using spin states the quantum Hall effect offers an opportunity to perform transport measurements with spin-polarized electrons in individual edge states at low filling factors. Suitable Hall bar devices consisting of MOS field effect transistors with embedded split-gates under the top gate have been fabricated. When characterizing the devices at 1.5 K and magnetic fields up to 8 T Shubnikov–de Haas measurements indicate, that filling factors as low as 1/2 corresponding to a single filled edge state can be realized. Transport through constrictions induced by the split-gates shows fluctuations which can be interpreted as the effect of transmission resonances in a one-dimensional channel such that the peaks at the lowest top gate voltage correspond to single mode states in the channel. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Silicon; Quantum Hall; MOSFET; Split-gate; 1D transport 1. Introduction Spin-polarized electrons exist in the edge states of two- dimensional electron gases (2DEG) at high magnetic fields in the quantum Hall regime. Transport measurements on individual edge states enable the investigation of scattering processes between them. Recently spin states in silicon have attracted attention for quantum computing since the main isotope of silicon has no nuclear spin. This means that the probability of spin scattering of the electrons with the base material is much lower than that in GaAs based systems. As a consequence the life times of the spin-polarized elec- trons are expected to be significantly longer. They can in principle be used for the detection of nuclear spin states of specifically implanted phosphorus atoms which are suit- able as quantum bits in quantum computers [1]. Here Hall bar structures on the basis of MOS-transis- tors with chromium split-gates below a Ti/Al topgate were fabricated to determine possible spin-flipping electron transfer between edge states, similar to experiments with AlGaAs heterostructures [2,3]. 2. Fabrication A schematic illustration of the process flow for the device fabrication is given in Fig. 1. It is similar to that of Khoury et al. [4]. First a Si(1 0 0) wafer with a resistivity of 5–10 X cm with 50 nm thermal oxide on top was struc- tured by optical lithography and subsequent reactive ion etching (RIE). The fabricated trenches had a depth of 170 nm and were used for alignment (Fig. 1(a)). Afterwards the wafer was structured by optical lithogra- phy and a subsequent removal of SiO 2 with buffered HF to define the areas where the silicon will be doped with phos- phorus. The doping was carried out in a furnace with pla- nar diffusion sources at 950 °C for 120 min in argon at a constant flow rate (Fig. 1(b)). The SiO 2 was removed with HF and the wafer was cleaned using standard RCA clean 1 and 2. The sample was dipped in HF to remove a newly formed layer of SiO 2 and rinsed with de-ionized water (DI) for 1 min. Then an 18 nm thick layer of thermal oxide was grown in a fur- nace at 900 °C(Fig. 1(c)). With electron beam lithography split-gates were defined in 200 nm PMMA 2010. The resist was developed in MIBK:isopropanol = 1:3 at 24 °C for 30 s (Fig. 1(d)). 0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.188 * Corresponding author. E-mail address: carsten.kentsch@uni-tuebingen.de (C. Kentsch). www.elsevier.com/locate/mee Microelectronic Engineering 83 (2006) 1753–1756