SPECTRAL AND RECOMBINATION CHARACTERISTICS OF SILICON COATED WITH TUNGSTEN AND HEAT-TREATED AT HIGH-TEMPERATURES

The effect of tungsten coating on the spectral and recombination chara cteristics of float-zone silicon subjected to cyclic heat treatment wi th a maximum temperature of 1100 degrees C was studied. The results sh ow that the change in the resistivity of tungsten-coated samples is sm all compared to the large (severalfold) decrease in the resistivity of uncoated samples. The coating notably reduces-by about one order of m agnitude-the drop in photoconductive decay time caused by heat treatme nt and also reduces the photon absorption cross section in the photon- energy range 0.56-1.00 eV. The photoconductive decay time as a functio n of temperature follows a power-law dependence with exponents beta(1) = 1.75 +/- 0.06 and beta(2) = 0.50 +/- 0.03 for tungsten-coated and u ncoated samples, respectively. One distinctive feature of the tungsten -coated samples is a nonmonotonic variation of the steady-state photoc onductivity relaxation time with additional illumination intensity at lambda = 1.056 mu m.