Optical absorption in epitaxial PbTe films on BaF2

Abstract

PbTe and Pb0.8Sn0.2Te epitaxial films on cleaved BaF2 substrates prepared by a modified hotwall technique Results are presented for below-band-gap (A~5-12 jJ.m) optical-absorption measurements at 300 and 77 K on epitaxial p-type PbTe films grown on BaF z . These results indicate a significant reduction in the absorption previously reported on PbTe epitaxial films on NaCI substrates. A few samples show an additional absorption suggestive of impurity effects. He 4 ion-backscatter spectra of these films show a surface contamination of chlorine. The results of room-temperature optical-absorption measurements on less contaminated samples agree reasonably well with bulk sample behavior. In low-carrier-concentration films (p < 10 17 cm-3 ) impurity effects appear to eliminate any temperature dependence of the absorption. The presence of the surface contamination does not affect the dc transport or refractive-index properties.

Lead Telluride (PbTe)

“…The refractive-index data compare favorably with those of Piccioli et al [10], Zemel et al [9], and McCarthy et al [21]; only in the region near the absorption edge are there some differences (see Table XI). Scanlon's data [24] for k are substantially lower (about 40~) than those of Globus et al [11].…”

“…It turns out that for carrier densities below 1019 cm-3, the values of e~ are also independent of electron concentration N. In the region below and around the fundamental absorption edge, optical constants have been determined and discussed in a number of works [9][10][11][21][22][23][24][25][26][27][28]. Early precise measurements on the refractive index in the 0.1-0.5-eV range were performed by Zemel et al [9] on epitaxial films by using an interferometric and weighing technique with an experimental error in n of about _+ 3~.…”

“…The error in refractive index is estimated to be _+ 1~ and in absorption index _+ 5~. McCarthy et al [21] investigated PbTe films on BaF2 substrates in the 5-12-#m range and showed that a significant reduction in absorption occurs below the band gap as compared with PbTe-NaC1 films, presumably due to chlorine surface contamination. McCarthy et al [21] investigated PbTe films on BaF2 substrates in the 5-12-#m range and showed that a significant reduction in absorption occurs below the band gap as compared with PbTe-NaC1 films, presumably due to chlorine surface contamination.…”