0
$\begingroup$

In an intrinsic material, the lifetime $\tau$ of electrons and holes is the same, so in the equation for mobility, $$\mu = \frac{e\tau}{m^*}$$ the only difference between mobility of electrons an holes is their effective mass, $m^*$. But why would this mass be different if it represents the same phenomena?

$\endgroup$
0
$\begingroup$

Even in an intrinsic material, $\tau$ is different for electrons and holes. This is because in the equation for $\mu$, the value of $\tau$ is not lifetime but rather the average time between scattering events. Since holes aren’t an actual particle, the movement of holes is really the movement of electrons in the valence band. Because there are many more electrons in the valence band than in the conduction band, electrons in the valence band scatter much with other electrons than electrons in the conduction band do. Therefore, $\tau$ for holes is smaller than tau for electrons, making the mobility of holes less than that of electrons in most (if not all) semiconductors.

As for effective mass, holes and electrons exist in different energy bands. Since different bands have different E vs. k(momentum) relationship, the effective mass in different bands is different. The E vs. k relationship is due to quantum mechanical effects for which there is not an easy physical explanation.

$\endgroup$
0
$\begingroup$

The effective masses are different because they are on different bands with different curvatures.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.