Growth and characterization of Bi-doped PbS thin films prepared by hot-wall epitaxy

We have investigated Bi-doped PbS thin films (Bi less than or equal to 5.23 mol%) prepared by hot-wall epitaxy. Infrared absorption by free carrier was observed on the transmission measurement by FT-IR. The relation between the absorption coefficient a and the carrier concentration n is expressed as follows: alpha = 4.53 x 10(-17) n(1.03) at 10 mu m. The high carrier concentration is obtained above 10(19) cm(-3) with n-type conductivity due to the doping of Bi in the films. Optical absorption edge shifts toward the larger frequency in proportion to the carrier concentration. The measurements of full-width at half-maximum (FWHM) of the X-ray diffraction patterns suggest that it is important to suppress the amount of Bi concentration in PbS thin films below about 1.5 mol% for obtaining excellent crystallinity.