Optical absorption in amorphous Si films at high pressure

We report the pressure-dependent optical absorption in the fundamental edge region of amorphous silicon prepared by sputtering and glow discharge methods. For pressures up to 20 kbar we find a negative pressure coefficient of about 1 ×{} 10^-6 eV/bar for the isoabsorption energies. In a higher range of pressure, starting with pressures of about 50 kbar, we observed irreversible red shifts in the absorption curves.