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The Electron Drift Instrument (EDI) on the Magnetospheric Multiscale (MMS) mission measures the in-situ electric and magnetic fields using the drift of a weak beam of test electrons that, when emitted in certain directions, return to the spacecraft after one or more gyrations. This drift is related to the electric field and, to a lesser extent, the gradient in the magnetic field. Although these two quantities can be determined separately by use of different electron energies, for MMS regions of interest the magnetic field gradient contribution is negligible. As a by-product of the drift determination, the magnetic field strength and constraints on its direction are also determined. The present paper describes the scientific objectives, the experimental method, and the technical realization of the various elements of the instrument on MMS.

Fully relaxed, high-quality Ge layers were grown directly on Si(001) substrates by surfactant-mediated epitaxy at high temperature with large Sb flux. We attribute the low dislocation densities in our films to an abrupt strain relief via the formation of a regular array of 90° dislocations at the interface during the initial, microrough stage of growth. This mechanism of abrupt strain relaxation occurs exclusively under high Sb coverage at temperatures ∼700°C. The high growth temperature also enhances Sb segregation leading to a low background doping level of only (3–4×1016)cm−3. Thus, we regard surfactant-mediated epitaxy of relaxed Ge on Si(001) as a promising candidate for device application.

Results on the in-plane electron drift velocities and mobilities in strained Si layers grown on Si1−xGex substrates are reported for 300 and 77 K. High-field drift velocities are calculated by Monte Carlo simulations and low-field mobilities by numerical solution of Boltzmann’s equation including intra- and intervalley phonon and impurity scattering mechanisms. Significant improvements of drift velocities relative to bulk Si are found for electric fields up to several 10 kV/cm, while saturation occurs at the bulk values for both temperatures. A much stronger mobility enhancement of 74% is obtained at 300 K compared to 36% at 77 K, which is consistent with recent experimental results.

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