Optical Constants of Zinc-Sulfide and ZINC-SULFIDE:MANGANESE Thin Films from 1.5 EV to 3.2 EV as Determined by Transverse Photothermal Deflection Spectroscopy.

Optical constants over the spectral range 1.5 -3.5 eV have been determined for pure and manganese doped zinc sulfide films using both transmission spectroscopy and transverse photothermal deflection spectroscopy (TPDS). TPDS is especially well suited for use in the spectral region of the conduction band tail where the optical absorption is sufficiently small so as to make the use of standard transmission and reflection spectroscopy impractical. The theory of photothermal absorption spectroscopy as applied to measuring the optical absorptance A of a thin film including interference effects is discussed. Our results for n in thin film ZnS are similar to the refractive index for thin film ZnS found by other workers. The differences between n in our films and that of bulk ZnS can be attributed to our films having a slightly lower density than bulk zinc sulfide. The values of k we determined differ markedly from those obtained from bulk samples and from some thin film results. This may be due to differences in the methods by which k is obtained in bulk reflectance spectroscopy and by fabrication differences between our samples and others. Oxygen impurities may lead to a larger absorption in our samples as compared to thin films that are prepared under better vacuum conditions. The energies of the d to d transitions within the Mn^{2+} dopant are found and compared to those found for bulk and powdered ZnS:Mn. A manganese concentration dependent background absorption was examined. This may be due to manganese -induced defect states that are considered important in the operation of thin film ZnS:Mn electroluminescent devices.