The mobility of charge carriers increases with

Increase in average collision time interval Increase in the electric field Increase in the mass of the charge carriers Decrease in the charge of the mobile carriers

Increase in average collision time interval

We know, Mobility µ = \(\frac{v_d}{E}=\frac{\left(\frac{e E}{2m}\right) \tau}{E}\) ∴ µ = \(\left(\frac{e}{m}\right) \tau \) The mobility of charge carriers depends on average relaxation (collision) time.