Microplasma Fluctuations in Silicon

The electrical properties of a fluctuating bistable microplasma are specified by three parameters which, in general, are functions of voltage. For an ideal low impedance connection, these parameters are independent of time and thus yield simple forms for the pulse rate, average current, differential conductance, and noise spectral density. With a high impedance circuit the phenomenon is more complex, and only an approximate analysis is offered. Measurements on alloyed junctions with breakdown voltages between 7.9 and 10.5 v show that single breakdown regions sometimes occur at low currents. Multistable conduction as well as the simpler bistable conduction is observed. The multistable conduction is characterized by fluctuations among higher current levels which occur at a rate 102–105 times faster than the ``on-off'' fluctuations. Excellent agreement between measured and calculated current spectral density at low impedance is found. This justifies the assumptions of random events independent of previous ``on'' or ``off'' time and suggests that noise spectrum measurements at low impedance be used as a tool for accurately determining the microplasma parameters. With a high impedance connection, the process is not Markoffian; thus the noise is not simply related to the noise at low impedance. The event which initiates breakdown is found to be field dependent suggesting that field emitted carriers are involved. It is shown that the results do not fully agree with those predicted by Rose's model of a microplasma.