On the Threshold of Current Saturation in GaAs

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Abstract
Current saturation in n-GaAs was investigated between 77°K and room temperature. Measurements were made of the dependences of the threshold electric field of saturation and the saturation drift velocity both on temperature and carrier concentration. It was shown that there are two types of current saturation, one of which occurs at low threshold electric fields (200∼500 v/cm) in a low temperature range while the other was observed at high threshold fields (1000∼3000 v/cm). The former is believed to be caused by an electron-phonon instability via piezoelectric coupling and the latter to be associated with a bulk negative differential conductivity due to electron transfer between two band minima with different effective masses. In the former, the saturation drift velocity exceeds the sound velocity. This was qualitatively explained by using the phonon-amplification theory by Hutson and Akhieser's theory of a linear loss of phonons. A simple calculation was made of the temperature dependence of the threshold electric field of the latter current saturation based on the Hilsum's model and the result was in a qualitative agreement with experiments.