Infrared dielectric constant of gallium arsenide

The real dielectric constant of gallium arsenide has been determined at 300 and at 5 K from fits to observed interference in transmission of thin samples with parallel surfaces. Measurement was carried out over all or part of the range 30–4000 cm−1. An accuracy of ±0.5% is estimated based on the quality of the analytic fits and the sample thickness measurement technique. We find at 300 K, ε0=12.90 and ε∞=10.86. At 5 K, ε0=12.46 and ε∞=10.58. An analytic expression for the dielectric function is given which allows accurate values of the real dielectric constant to be determined throughout most of the 0–4000 cm−1 spectral range. The observed ratio ε0/ε∞ agrees with the Lyddane–Sachs–Teller relation calculated with Raman values of transverse and longitudinal optical phonon frequencies to better than 0.1% at 300 and at 5 K.