We report Larmor precession in bulk InSb observed in the time domain from 77 to 300 K. The optically oriented polarization precesses coherently even at 300 K. The inferred Zeeman spin splitting is strongly nonparabolic, and the electron g factor ͑g * ͒ is in good agreement with k · p theory ͑provided we take only the dilational contribution to the change in energy gap with temperature͒. We also show here that correct application of the 14-band k · p model agrees with apparently anomalous trends previously reported for GaAs and confirm that the most widely quoted formula for g * in GaAs is incomplete. DOI: 10.1103/PhysRevB.77.033204 PACS number͑s͒: 72.25.Fe, 71.70.Ej, 72.25.Rb, 78.47.-p InSb is an interesting semiconductor from the point of view of tests of semiconductor band structure calculations because the heavy constituent atoms produce large relativistic effects such as spin-orbit coupling ͑responsible for the large, negative gyromagnetic ratio͒. InSb is also a candidate material for room-temperature spintronic devices such as the Das-Datta spin transistor, which relies on a coherent spin population manipulated by the Rashba effect, and thus, detailed investigation of the spin-electronic structure in this material at room temperature is of high topical interest. In the present work, we report the experimental measurement of the g factor in InSb at temperatures up to 300 K and the theoretical evaluation of g * ͑T͒ for both InSb and GaAs.Although it has been claimed that measurements of the g factor of GaAs at 300 K are inconsistent with k · p perturbation theory, 1-4 this theory has been successfully used for decades to calculate the band structure in bulk semiconductors and heterostructures, [5][6][7][8][9][10][11][12][13][14] and, in particular, the conduction band effective mass and g factor. We show here that provided we include only the dilational change of the energy gap with temperature, 8,13 we obtain reasonable agreement between experiment and theory for the high-temperature g factor in both InSb and GaAs, and there is no anomaly. The higher band k · p parameters have only a very small effect on the electron g factor for InSb, but they are very important for GaAs; in particular, we confirm that it is essential to include the effects of the interband spin-orbit coupling parameter, which was previously ignored in the Hermann and Weisbuch formula for g * ͑Ref. 9͒ used in Refs. 1 and 2.In an externally applied magnetic field, the electron energy is given bymeasured from the ⌫ 6 conduction band edge, where B is the Bohr magneton, the quantum numbers Ϯ refer to the spin, n to the Landau level index, and k B to the component of momentum parallel to the magnetic field B. In the parabolic approximation, the effective mass and g factor, m * and g * , are constants and independent of n, k B , and B. The nonparabolicity of GaAs is usually taken to be small because the dependence of the effective mass on electron energy is small. 7 However, the g value, although small in magnitude, is significantly nonparabo...

The spin relaxation in undoped InSb films grown on GaAs has been investigated in the temperature range from 77 to 290 K. Two distinct lifetime values have been extracted, 1 and 2.5 ps, dependent on film thickness. Comparison of this data with a multilayer transport analysis of the films suggests that the longer time ͑ϳ2.5 ps at 290 K͒ is associated with the central intrinsic region of the film, while the shorter time ͑ϳ1 ps͒ is related to the highly dislocated accumulation region at the film-substrate interface. Whereas previous work on InAs films grown on GaAs showed that the native surface defect resulted in an additional charge accumulation layer with high conductivity but very short spin lifetime, in InSb layers the surface states introduce a depletion region. We infer that InSb could be a more attractive candidate for spintronic applications than InAs.

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Simulation of x-ray generation from bombardment of various solid targets by quasimonoenergetic electrons is considered. The electron bunches are accelerated in a plasma produced by interaction of 500 mJ, 30 femtosecond laser pulses with a helium gas jet. These relativistic electrons propagate in the ion channel generated in the wake of the laser pulse. A beam of MeV electrons can interact with targets to generate x-ray radiation with keV energy. The MCNP-4C code based on Monte Carlo simulation is employed to compare the production of bremsstrahlung and characteristic x rays between 10 and 100 keV by using two quasi-Maxwellian and quasimonoenergetic energy distributions of electrons. For a specific electron spectrum and a definite sample, the maximum x-ray flux varies with the target thickness. Besides, by increasing the target atomic number, the maximum x-ray flux is increased and shifted towards a higher energy level. It is shown that by using the quasimonoenergetic electron profile, a more intense x ray can be produced relative to the quasi-Maxwellian profile (with the same total energy), representing up to 77% flux enhancement at K energy.

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