Structural and Optical Properties of the Thermally Stable Amorphous Si1−xBx Alloy.

Thin amorphous Si1−xBx films were co-evaporated onto pre-oxidized (100) Si wafers and quartz substrates, by using a high vacuum system with 2 electron guns. Films were deposited in a composition range from x=0 to x=0.5. In order to study how the structural and optical properties depended on concentration and annealing temperature, heat treatments were carried out at temperatures from 400 up to 1000°C. The films were characterized by means of transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and light absorption spectrophotometry. It is shown that the amorphous Si1−xBx alloy is stable up to 1000°C at certain compositions and that the optical band gap of the alloy increases gradually with increasing annealing temperature up to 700 - 900°C, and then increases rapidly when annealed at a higher temperature by about 0.5 eV. These changes can be associated with microstructural alterations. The relationship between the microstructure and the band gap of the films is discussed.