Spin-spin scattering in a silicon two-dimensional electron gas

The scattering of conduction electrons by neutral impurities in Si has been demonstrated through measurements of spin-dependent transport (SDT) in a two-dimensional electron gas (2DEG). SDT was observed by monitoring the conductivity of a specially fabricated Si accumulation layer transistor operating at 4 K while modulating the electron-spin populations. By utilizing the differences in the singlet and triplet state scattering cross sections, the technique provides the first direct measure of neutral impurity scattering. The SDT spectrum consists of a pair of hyperfine peaks separated by 42 G which are assigned to the impurity electron system and a broad central feature which is attributed to both the conduction spins and donor spins with strong exchange interactions. A phenomenological theory for the resonant change in device current is developed and comparison of theory with experiment indicates that the interaction of a 2DEG with neutral impurities must be treated two dimensionally; scaling the known 3D scattering cross sections to their 2D counterparts is inappropriate. Numerical simulations of the SDT line shape are obtained by modeling the spin dynamics. The possibility of alternative explanations for the observed signal, such as bolometric detection of the electron-spin resonance, are explored and eliminated. The SDT spectrum is characterized as a function of temperature, microwave power, Fermi energy of the 2DEG, and magnetic-field orientation. A lower bound for 〈${\mathrm{\Sigma }}_{\mathit{s}}$-${\mathrm{\Sigma }}_{\mathit{t}}$〉, the difference in singlet and triplet scattering cross sections integrated over angle and position of the donor impurity, is obtained as a function of the Fermi energy. A spin-dependent signal from ∼${10}^8$ spins was observed, which demonstrates the enhanced sensitivity of SDT over conventional electron-spin-resonance methods.