Mobility of Carriers in Nondegenerate Semiconductors at Low Electric Fields

By using the velocity distribution of carriers in the presence of an electric field $E$, due to Yamashita and Watanabe, it is shown that the mobility $\mu$ is given by $\mu ={\mu }_0(1+\beta E^2)$ for low fields. The values of $\beta$ obtained are larger than those arrived at by the assumption that the distribution is Maxwellian in the presence of an electric field. The discrepancy between the theoretical and observed values of $\beta$ is large enough to justify further careful examination of the theory of the perturbing effect of weak fields.