HIGH-FIELD TRANSPORT IN SEMICONDUCTORS .1. ABSENCE OF THE INTRA-COLLISIONAL-FIELD EFFECT

We show that the Levinson (Zh. Eksp. Teor. Fiz. 57, 660 (1969) [Sov. Phys.-JETP 30, 362 (1970)]) quantum transport equation reduces to the semiclassical Boltzmann equation in the limit of a strong homogeneous electrostatic field. To arrive at this conclusion we use a saddle-point approximation which has not been used in this field before. This approximation is exact in the high-field limit. We show that even for a relatively moderate field strength of 3 x 10(5) V/m in GaAs (even before the onset of the Gunn effect, when 90% of the electrons are still in the central valley) the saddle-point approximation can be used for a majority of the scattering events. The results in this paper are supported by numerical calculations based on realistic scattering mechanisms in GaAs.