Structural and electronic properties of ternary hydrogenated amorphous silicon-sulfur-selenium alloys

M. Hammam, S. M. Al-Alawi, B. Al-Alawi, S. Al-Dallal, S. Aljishi, M. Stutzmann

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Hydrogenated amorphous silicon-sulfur-selenium ternary alloys are grown by rf glow discharge. Results show that alloying a-Si:H with S and Se results in an increase in the optical gap from a value of 1.85 eV in unalloyed films to approximately 2 eV in films grown with a chalcogenide gas fraction of 0.8. IR absorption spectra reveal a clear Si-S stretching vibrational mode which grows in intensity with increasing S content. In addition, the spectra display a pronounced shoulder in the region of 700 to 760 cm-1 which is attributed to a superposition of S2, Se2 and SiS vibrational modes. Most of the bonded hydrogen in the alloy films occurs in the form of polyhydrides. PDS measurements of the subgap optical absorption in 2.0 eV Eopt material reveal a broad exponential Urbach tail with a slope of approximately 92 meV. The tail saturates into a defect absorption shoulder at a value of approximately 102 cm-1, indicating that the deep defect density is on the order of 1017 to 1018 cm-3. The alloys display substantial photosensitivities as the dark conductivity values range between 10-12 and 10-10 S/cm and the photoconductivities, measured at 100 mW/cm2 illumination intensity, lie at approximately 10-8 S/cm.

Original languageEnglish
Pages (from-to)911-914
Number of pages4
JournalJournal of Non-Crystalline Solids
Issue numberPART 2
StatePublished - 1991
Externally publishedYes


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