Small angle neutron scattering in p(+)-doped porous silicon

On the surface of single crystal silicon wafers, porous layers can be forme d by electrochemical etching and their structural properties are determined by the doping type and concentration of the substrate. In p(+)-type doped, (1 0 0) oriented wafers the porous structure consists of "tube-like" voids and "column-like" remains of the silicon matrix, all perpendicular with re spect to the wafer surface. In small angle neutron scattering experiments t he micrometer long and nanometer diameter elongated scattering elements, i. e., tubes and columns can be well represented and approximated by cylindric al form factors. In an earlier experiment the diameter and scattering lengt h distribution of the cylindrical scattering elements were measured in a p( +)-type (1 0 0) oriented porous silicon wafer [G. Kadar, G. Kali, Cs. Ducso , and E.B. Vazsonyi, Physica B 234-236, 1014 (1997)] and the tube diameters were seen to vary in the range from about 10 to 24 nm. In this paper the c ontinuing small angle neutron scattering study of porous silicon layers wil l be presented. The evaluation conditions and method for the measured neutr on intensity distributions will be discussed. The pore diameter distributio n data calculated from the neutron scattering intensity curves are collecte d and compared in various samples of (1 0 0) oriented p(+)-doped wafers pre pared with different porosity and different layer depth. The structural res ults and data obtained by small angle neutron scattering experiments may he lp in understanding the practically useful chemical, electronic and other p roperties of porous silicon.