Effective Electron Mass and Plasma Filter Characterization of n-Type InGaAs and InAsP

We measured the infrared reflectance of thin films of degenerate n-type In _xGa _1-xAs and n-InAs _yP _1-y as a function of doping for compositions that correspond to x=0.53, 0.66, and 0.78 (band gaps of 0.74, 0.60, and 0.50 eV, respectively) and y=0.00, 0.31, 0.52, and 0.71 (band gaps of 1.34, 1.00, 0.75, and 0.58 eV, respectively). We then used the Drude theory and Hall measurements to determine the effective electron mass for these samples, and checked the results using Raman spectroscopy. The effective electron mass for these compositions increases abruptly as a function of free-electron density and converges at 5×10 ¹⁹ electrons/cm ³. Consequently, it is difficult to attain plasma edges at wavelengths shorter than 5 μm using these materials, and the plasma edge is nearly independent of composition at large electron density levels. Results from similar studies on InP, InAs, and GaAs have been compiled and compared with our data. It is clear that the Kane band model offers an accurate description of the conduction-band nonparabolicity.