The Influence of Boundary Conditions on Current Instabilities in GaAs

We obtain excellent agreement among experiments eliciting a variety of GaAs current instabilities and the results of a computer simulation of GaAs with various fields imposed at the cathode boundary. When the cathode field is below around 4 kV/cm theory and experiments show that the I–V characteristics of the active element are linear up to about 3 kV/cm where the current saturates and no transit-time oscillations occur. Experimentally this element gives rise to severe noise in a resistive circuit and sometimes tunable oscillations in a resonant circuit. When the cathode field is in the differential negative resistivity regime the I–V characteristics of the active element are nearly linear up to a threshold field (determined by the boundary field) where current drop, voltage rise and transit-time oscillations occur. For cathode fields above about 15 kV/cm the I–V characteristics are nonlinear and the element exhibits tunable oscillations in a resonant circuit.