Optical thickness changes in freshly deposited layers of Lead Telluride
C S Evans, R Hunneman, J S Seeley
Journal of Physics D, Vol 9, Pages 321-328 (1976)
An increase or growth of optical thickness has been observed in PbTe layers freshly deposited during infrared filter manufacture. The phenomenon is nine parts complete about 15 min after deposition ceases, and is typically 0.03 µm thick but can vary between 0.005 and 0.09 µm. Fluctuations in receptor surface temperature have been eliminated from being responsible for any part of the growth; negligible correlation is also found with physical thickness, monitoring wavelength (3.4-5 µm), deposition temperature, receptor surface and underlying layers. An un-quantified correlation appears to have been found with deposition rate. Undesirable loss of transparency accompanies any attempt at suppressing the phenomenon; conversely, when allowed to proceed without inhibition the growth sets up errors in the filters being manufactured, requiring individual compensation.