Electron Beam Modulated Optical Properties of Semiconductors

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Abstract
The electron beam of an electron probe microanalyzer has provided a new method of modulating the reflectance and absorption of light by semiconductors. The beam is periodically gated and the modulated light detected synchronously. The relative reflectance spectra of Ge, Si, GaAs, and GaP exhibit features at photon energies above the bandgap which resemble thermoreflectance of critical point transitions. An analysis of the possible modulation mechanisms and experiments involving gating frequency and beam density indicate that the modulation is due to temperature variations from the electron‐beam heating. Modulated reflectance of light with photon energies below the bandgap of Ge and GaAs was measured and found to be attributable to the temperature coefficient of the real part of the refractive index. Electronbeam modulated absorption of long‐wavelength light was observed and found to be due to excess carriers generated by the beam.

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