Contribution to the experimental study of the Gunn effect in long GaAs samples

We describe some experimentally observed features of the Gunn effect in long samples (0.1 to 0.4 cm) of GaAs with a resistivity of 1 to 4 Ω. cm at room temperature. The normal behavior of current oscillations and the effect of inhomogeneities may be well understood qualitatively if we take into account the characteristic of the excess voltage in the high-field domain versus the electric field outside it. Thus it is shown that when a domain moves through a sample with doping inhomogeneities, its velocity remains almost constant at every point inside the specimen whereas the current fluctuation is rather large from one region to another. Fields in excess of 130 kV/cm were found to exist in domains which always present a triangular shape. Changing the starting point of a domain has been easily achieved by putting a grounded wire along the side of a long sample. We report also the following new phenomena: a) Transient changes in material conductivity in normal conditions of operation and also when a sample containing a high-field domain is subjected to an additional negative voltage spike. b) Recombination radiation in specimens with a resistivity of 1 to 4 Ω. cm operated in the trigger mode. This emission is associated with a switching of the current, and correspondingly the domain takes a new configuration in which the maximum field is only 25 kV/cm. c) Migration of tin due to the effect of the high-field domain. At each domain transit, the length of migration is about 4 Å.