Magnetotransport studies of mobility limiting mechanisms in undoped Si/SiGe heterostructures

Abstract

We perform detailed magnetotransport studies on two-dimensional electron gases (2DEGs) formed in undoped Si/SiGe heterostructures in order to identify the electron mobility limiting mechanisms in this increasingly important materials system. By analyzing data from 26 wafers with different heterostructure growth profiles we observe a strong correlation between the background oxygen concentration in the Si quantum well and the maximum mobility. The highest quality wafer supports a 2DEG with mobility µ = 160,000 cm 2 /Vs at a density n = 2.17 ×10 11 /cm 2 and exhibits a metalto-insulator transition at a critical density nc = 0.46 × 10 11 /cm 2 . We extract a valley splitting ∆v ∼ 150 µeV at a magnetic field B = 1.8 T. These results provide evidence that undoped Si/SiGe heterostructures are suitable for the fabrication of few-electron quantum dots.

Scattering mechanisms in shallow undoped Si/SiGe quantum wells

“…This number is of the same order of magnitude of what has been reported in the literature. 28,35,36 We obtain an exponent of α ∼ 1.6, thus confirming the validity of our numerical method within the RPA. 33 To model the non-equilibrium screening effect, we add a number of negative charges based on the difference between the extrapolated linear portion of the curve in Fig.…”

“…A common approach to experimentally determine the dominant scattering mechanisms in two-dimensional systems is to extract the power-law exponent from the density dependence of the mobility. Several experimental and theoretical studies have used similar techniques to analyze disorder in GaAs/AlGaAs structures, [15][16][17][18][19][20][21] Si MOSFETs, 22 and doped 4,[23][24][25] and undoped [26][27][28] Si/SiGe heterostructures. With this in mind, we present in this work a systematic study of the depth dependence of scattering mechanisms in undoped shallow Si/SiGe quantum wells with channel depth ranging from 100 nm to only 10 nm away from the surface, the shallowest Si/SiGe device reported to date.…”

Single-Spin Relaxation in a Synthetic Spin-Orbit Field

“…We measure T 1 as a function of external magnetic field B ext on two devices (see Fig. 1) fabricated from the same Si/SiGe wafer used in previous experiments [37,38] . Electrons in the Si quantum well are laterally confined using an overlapping aluminum gate architecture [38].…”

Circuit quantum electrodynamics architecture for gate-defined quantum dots in silicon

“…23,24 A 3 lm thick linearly graded Si 1Àx Ge x relaxed buffer substrate is grown on top of a Si wafer (resistivity >5000 X cm). The buffer is chemically and mechanically polished before the growth of a 170-375 nm thick Si 0:7 Ge 0:3 layer, an 8 nm thick Si quantum well (QW), a 50-60 nm thick Si 0:7 Ge 0:3 spacer, and a 2-4 nm thick Si cap.…”