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Recent advances in laser and semiconductor device technology have generated a growing concern over the validity of the standard transport theory in the limit of small length scales, high frequencies, and high field intensities. This has necessitated a reexamination of the foundations of transport theory and the necessary quantum extension in these limits. In this paper, the response of free carriers in a polar semiconductor to a high frequency electric field is examined. A frequency dependent relaxation time has been derived for free carriers in polar semiconducting compounds with the band structure of the Kane theory from a quantum extension of the Boltzmann transport equation. The expression obtained reduces to the usual quasiclassical Boltzmann result in the limit of low frequencies, elastic scattering mechanisms, and parabolic bands, and gives the quantum result at high frequencies when used in the Drude Zener formula for the optical conductivity. A high frequency extension of the Drude theory is thus obtained which gives the observed λ3 dependence of the absorption coefficient characteristic of polar scattering in III–V and II–VI compounds in the near infrared, and reduces to the usual λ2 dependence at sufficiently low frequencies. At high intensities, the scattering rate becomes a function of field intensity.
Numerical results for the electron scattering rate are calculated as functions of frequency and carrier concentration and compared with available experimental data for a number of III–V compounds.
Laser damage, optical constants, optical materials, semiconductors, stimulated bremsstrahlung absorption, wavelength dependence
Boston University, Boston, Massachusetts