
Physics of Semiconductor Devices 

Impurity scatteringWhen a semiconductor is doped, the mobility decreases due to impurity scattering. Undoped GaAs has an electron mobility of 8500 cm²/Vs at 300 K. After doping, the electron mobility reduces to 7000 cm²/Vs. What is the scattering time associated with impurity scattering? Hint: the total scattering time will be shorter than the scattering time associated with impurity scattering since there will also be scattering from phonons. The effective mass of electrons in GaAs is 0.067m_{e}. 