Correlation between optical properties and chemical composition of sputter-deposited germanium oxide (GeOx) films

• Published in: Optical materials Vol. 36; no. 7; pp. 1177 - 1182
• Main Authors: Murphy, N.R., Grant, J.T., Sun, L., Jones, J.G., Jakubiak, R., Shutthanandan, V., Ramana, C.V.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01.05.2014; Elsevier
• Subjects: Chemical composition; Constants; Correlation; Direct current; Ellipsometry; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Germanium; Germanium oxide; Germanium oxides; Optical materials; Optical properties; Optics; Oxides; Physics; Reactive sputtering; X-ray photoelectron spectroscopy; Reactive sputtering; Germanium oxide; X-ray photoelectron spectroscopy; Ellipsometry; Spectroscopic ellipsometry; Grazing incidence; Germanium Oxides; Binary compounds; Optical properties; Germanium; X radiation; Optical materials; Optical constants; X-ray photoelectron spectra
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2014.02.023

•Measurement of refractive index and extinction coefficient of GeOx (0<x<2).•Spectral refractive index for GeO2 ranges from 1.66 to 1.60.•GeO2 obtained at oxygen fractions of 50% and above.•Compounds obtained include Ge, GeO, and GeO2.•Correlation shown between oxygen fraction, optical constants, and chemical composition. Germanium oxide (GeOx) films were grown on (100) Si substrates by reactive Direct-Current (DC) magnetron sputter-deposition using an elemental Ge target. The effects of oxygen gas fraction, Г=O2/(Ar+O2), on the deposition rate, structure, chemical composition and optical properties of GeOx films have been investigated. The chemistry of the films exhibits an evolution from pure Ge to mixed Ge+GeO+GeO2 and then finally to GeO2 upon increasing Г from 0.00 to 1.00. Grazing incidence X-ray analysis indicates that the GeOx films grown were amorphous. The optical properties probed by spectroscopic ellipsometry indicate that the effect of Г is significant on the optical constants of the GeOx films. The measured index of refraction (n) at a wavelength (λ) of 550nm is 4.67 for films grown without any oxygen, indicating behavior characteristic of semiconducting Ge. The transition from germanium to mixed Ge+GeO+GeO2 composition is associated with a characteristic decrease in n (λ=550nm) to 2.62 and occurs at Г=0.25. Finally n drops to 1.60 for Г=0.50–1.00, where the films become GeO2. A detailed correlation between Г, n, k and stoichiometry in DC sputtered GeOx films is presented and discussed.