HOLOGRAPHY IN POROUS SILICON

Holographic structures have been obtained in porous silicon (PS) by ph otodissolution of the material in hydrofluoric acid under interferomet ric illumination. This process can be performed after or during the fo rmation of the PS layer. One-or two-dimensional structures have been e asily etched down to the submicron range. The photosensitivity is demo nstrated for the entire visible range. Because the dissolution process occurs in the bulk, the thickness of the structure is only determined by the penetration depth of the light in the material, which in the c ase of PS is about 0.1 to 15 mu m (from uv to 600 nm). The technique i s generalized to all types of nanoporous silicon. The efficiency of th e dissolution depends on the specific area of the porous material and the initial resistivity of the wafer. The structures have been charact erized by light diffraction. For this material, photoluminescence allo ws the topography of the porosity modulation to be determined precisel y. These results and the ease and low-cost fabrication of the PS layer make porous silicon a promising material for holography.