Question

Derive the expression of effective mass. In which condition the effective mass will be positive, negative and infinite?

Answer 1

Answer:

As one can see from the dispersion curves, the effective mass of the electrons in the valence band, m*V, is always negative. (This means that a force in +x direction will cause such an electron to move in –x direction.)

This mass of an electron is called the effective mass of an electron, denoted as m*. The effective mass is thus determined by d 2E/dK 2. From band theory of solids, we know E is not proportional to K 2.

The effective mass is a quantity that is used to simplify band structures by modeling the behavior of a free particle with that mass. For some purposes and some materials, the effective mass can be considered to be a simple constant of a material.