VISIBLE-LIGHT EMISSION FROM FREESTANDING FILAMENT CRYSTALS OF SILICON

We present the results of a photoluminescence study in naturally gown filament-like silicon crystals. It is shown that with the decrease of filament diameter from few tens to 0.1 mu m, the photoluminescence spe ctra transform from the ones of bulk silicon to completely new spectra . The spectra at 4.2 K consist of the narrow 1.139 eV band and several very nide visible (red, yellow, green, and blue) bands with the maxim um position ranging from 1.7 to 2.9 eV. The bands of visible photolumi nescence do not markedly change with the increase in temperature up to 300 K, while the 1.139 eV band disappears. The most striking result i s the appearance of visible light emission from crystals with transver se size much larger than the Bohr radius. The results obtained are dis cussed together with our previous ones obtained for these crystals, an d a possible model of the filament crystal structure as well as the or igin of visible photoluminescence are suggested.