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

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. By analyzing data from 26 different heterostructures, 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 mu = 160 000 cm super(2)/Vs at a density n = 2.17 x 10 super(11)/cm super(2) and exhibits a metal-to-insulator transition at a critical density n sub(c)= 0.46 x 10 super(11)/cm super(2). We extract a valley splitting Delta sub()v~ 150 mu eV 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.