Effect of free carriers on electron mass and infrared absorption in n-type CdGeAs2

The electrical and optical properties of n-type CdGeAs2 crystals doped with indium have been studied at room temperature using van der Pauw Hall measurements, infrared absorption, and infrared reflectance. Free-electron concentrations (n) in the sample set range from 2.3 x 1017 to 4.3 x 1018 cm-3 at 300 K. For the higher levels of free carriers, conduction-band non-parabolicity causes significant increases in electron effective mass m*. Infrared absorption due to free carriers is consistent with ionized impurity scattering, and absorption coefficients αf for different samples agree with theoretical predictions when the dependence of m* on n is included. A relation between αf and n has been determined for CdGeAs2:In that can be applied to large-sized samples used in nonlinear optical applications. The optical effective mass mopt* obtained from reflectance data is also in good agreement with predicted m* values for CdGeAs2