Free Carrier Absorption Due to Polar Modes in the III-V Compound Semiconductors

The longitudinal polar modes of vibration in the III-V compound semiconductors play an important part in determining their transport properties, such as mobility. One would therefore expect them to be important for free carrier absorption, as well, in these semiconductors. A quantum mechanical calculation of the free carrier absorption arising from these modes has been made and gives an absorption varying as ${\lambda }^{2.5}$, and such behavior has been reported experimentally in InP and GaP. The calculated value of the absorption coefficient in InP is in good agreement with experiment.