Current Oscillations in Deep-level Doped Semiconductors

We observe current oscillations in p-i-n (and optically excited n-i-n) devices containing deep levels. The oscillations occur in the positive resistance region of the space-charge-limited (SCL) current regime of the I–V characteristics, before the occurrence of double-injection breakdown. This is a general effect, occurring in Si, Ge, and GaAs compensated with various deep-level impurities and in electron-irradiated devices. The oscillations are sinusoidal at threshold, with frequency strongly dependent on the recombination kinetics of the i-region, and on the deep level density, but are essentially independent of device length. The frequency and amplitude of the oscillations are affected by temperature and optical excitation. Various models have been proposed to account for oscillations in semiconductors containing deep levels, but no existing model describes fully the various aspects of the effect reported here. Because the device length exceeds carrier diffusion length, any model for the oscillation mechanism must include the existence of space charge and the kinetics of recombination, but may not depend essentially upon a traveling domain which imposes a length dependence on the oscillation frequency. Tentatively, we favor a model in which the recombination process unbalances the steady or dc space charge.