Instabilities of electron-hole plasma under impact ionization and microwave emission

The nonlinear stage of the evolution of electron—hole plasma instabilities in semiconductors under impact ionization (static differential conductivity σ_d > 0) is considered for the case of spatially uniform pertubations of density and electric field. If the differential mobility of carriers μ _d > 0, the instability arises only with allowance for the retardation of the process of impact ionization (linear theory of this effect was developed by M. Toda [4]). When μ _d < 0, the instability may appear in the absence of the retardation. Both these instabilities exhibit oscillating form and are due to h.f. negative dynamic differential conductivity. We determine time sweeps of the electric field under condition of fixed current for the case n-InSb at T = 77 K. The amplitude and the frequency (f>10¹⁰Hz) of the oscillations are evaluated and the conditions, when the shape of E(t)-oscillations is essentially non-harmonic, are determined. Microwave emission observed in semiconductors under impact ionization may have resulted from the instabilities at hand.