Oscillations of a ballistic hole current through uniaxially compressed semiconductor layers

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Abstract
The oscillations of the ballistic hole current through a thin base of a p+pp+ diode compressed uniaxially in the direction of the current are investigated theoretically. As a result of compression, the hole dispersion relation contains sections with negative effective mass along the indicated direction. The current oscillations are caused by the instability of the stationary ballistic current-carrier distribution, which contains an extensive quasineutral plasma region in which the mobile component of the charges consists of drifting carriers with negative effective mass. In many cases, the current oscillations possess a harmonic character, whose frequency is determined by the length of the base and by the voltage, amounting to hundreds of gigahertz for long (∼1 µm), weakly doped bases and several terahertz for short (<0.1 µm), strongly doped bases. Criteria for a quasiclassical approach to the problem, which was used in the numerical modeling of the vibrational processes described here, are found. This approach is justified if the ballistically injected carriers are distributed in a sufficiently wide band of transverse momenta.