HYDROSTATIC-PRESSURE EFFECTS ON THE OPTICAL-TRANSITIONS IN THE FREESTANDING POROUS SILICON FILM

Optical absorption and photoluminescence spectra in the range 1.2-2.2 eV have been measured in free-standing films of porous Si under hydros tatic pressures up to 6.4 GPa at room temperature. The absorption rise s nearly exponentially in the low energy region. Under pressure, the w hole spectrum shifts toward lower energies with a pressure coefficient of about -90 meV/GPa. The photoluminescence spectrum also exhibits a redshift of about -40 meV/GPa. These results are interpreted by analog y with the pressure-induced shrinkage of the optical energy gap seen i n amorphous chalcogenide semiconductors.