Electron Effective Masses of InAs and GaAs as a Function of Temperature and Doping

The electron effective masses of several GaAs and InAs samples at room and liquid nitrogen temperatures have been determined from Faraday rotation and infrared reflectivity measurements. An increase in effective mass with increasing carrier concentration has been found in both materials. This increase can be quantitatively interpreted in InAs in terms of the nonparabolic nature of the conduction band. In GaAs the increase in effective mass with doping suggests the existence of another set of conduction band minima above the lowest (000) minimum. The measured temperature variation of the effective mass can be attributed to two mechanisms: the increase in effective mass produced by the spread in the Fermi distribution because of the nonparabolic shape of the band, and the variation in the band structure produced by the thermal expansion of the lattice.The Faraday rotation due to the interband transitions has been measured in GaAs and InAs. This rotation is clockwise along the direction of motion of the radiation and the magnetic field for GaAs and counterclockwise for InAs. This effect is compared with the corresponding effect in other semiconductors.