NNSE 618 Lecture #9 2 High field electron transport Hot electrons transfer energy into thermal vibrations of the crystal lattice (phonons). Such vibrations can be modeled as harmonic oscillations with a certain frequency, wph. The energy levels of a harmonic oscillator are equidistant with the energy difference between the levels equal to Two types of phonons scatter electrons differently: acoustical (slow) and optical (fast): Hence, process for a hot electron can be represented as follows. The electron accelerates in the electric field until it gains enough energy to excite optical phonon: phphEwmeVEoptopt40wkTEacacw
NNSE 618 Lecture #9 3 Saturation velocity due to optical phonon scattering If the energy relaxation occur through optical phonons, the energy-loss rate equation can be written as: A corresponding rate equation for momentum relaxation (vs–saturation velocity): Assuming the scattering by optical phonons as a dominant mechanism, in a steady state For typical values 01.0*mmmssvmedtdvm**opopsEevdtEd21*mEvoptsmeVEoptopt40wscmvs/1027
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