We present a detailed study on the oscillatory behavior of p-type germanium at the onset of avalanche breakdown at low temperatures. Measuring the frequency and amplitude of these oscillations as a function of different control parameters, such as average current, perpendicular magnetic field, and outer circuit conditions, we can clearly distinguish two different types of oscillations. For one, we found an oscillatory mechanism that depends on the outer electrical circuit. It describes the behavior in detail and also clarifies the connection between the dynamical behavior and the actual appearance of the current-voltage characteristic. Whereas this first type is the result of a global mechanism involving sample voltage and sample resistance, the second type results from a local oscillatory mechanism. Therefore, the more complicated dynamical structure can be understood as a result of the coupling between different localized oscillatory modes.

• Received 2 July 1990

DOI:https://doi.org/10.1103/PhysRevB.43.2255