# Mobility and transit time

Consider the 2.0micrometer long GaAs device where the E-field is 5kV/cm and Mn*=.067M0.

(a) Calculate the transit time of an electron through the device if the mobility is 8000 cm^2V-s.

(b) The mean free path of an electron (average velocity x scattering time) is the average distance an electron travels between two consecutive scattering events. Calculate the mean free path of a GaAs electron at room temperature.

(c) How does the mobility of a semiconductor depend on T? And why?

How did you do it, and what are the answers?

Thank you.

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#### Solution Preview

Compute the drift velocity and the mean time between collisions of the electrons. Please see attached.

The length of the GaAs is . The electric field is . The effective mass of electron is where kg (from the book)

(a) From , therefore

The transit time is the time for the electron to move through the device is then

(b) From , therefore

Therefore, the mean free path of the electron is

(c) The mobility of the carrier ...

#### Solution Summary

This solution provides in 308 words a step-by-step explanation for finding transit time and mean free path. The solution also discusses in detail phonon and ionized impurity scattering effects and how it relates to kinetic energy. The answer is given in an attached .doc file.