Depletion layers, plasmon dispersion, and the effects of temperature in degenerate InSb(100): A study by electron-energy-loss spectroscopy

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Abstract
High-resolution electron-energy-loss spectroscopy has been used to observe the effects of temperature on the excitation of the conduction-band electron plasmon in degenerate n-type InSb(100). Measurements of the intensity and energy of the plasmon loss at both 290 and 435 K were made over a wide range of incident electron energies. The data have been analysed using semiclassical dielectric theory and a depletion-layer model which incorporates a q-dependent surface loss function and spatial dispersion. As the temperature is increased the depletion layer is reduced from 100 Å at 290 K to 90 Å at 435 K. Accounting for the nonparabolic nature of the conduction band, the highly degenerate nature of InSb at these bulk doping levels, and a temperature-dependent bulk band gap, this decrease reflects the change in band bending which accompanies the lowering of the Fermi level as the temperature is raised. The changes in plasmon energy over this temperature range are not a consequence of any change in the free-carrier concentration.