Reflection and absorption spectra of b-FeSi2 under pressure

High-pressure optical reflection and absorption study of *b-FeSi2 were carried out up to 5.0 and 4.8 GPa, respectively at room temperature. By the absorption experiment, the pressure coefficient of the direct band gap was determined to be 15.9 meV/GPa. On the other hand, the pressure dependence of dielectric functions were obtained by using Kramers-Kronig relations for the reflection spectra and the pressure coefficients of three different higher energy gap were tentatively evaluated to be 8.73, 8.63 and 16.7 meV /GPa, respectively. These pressure coefficients are quite smaller than those of II-VI, III-V and group IV common semiconductors. We propose that the small pressure coefficient is caused by not only the larger bulk modulus compared with common semiconductors but also the shift of the valence band maximum of *b-FeSi2 to higher energy with increasing pressure.