Vibrational, optical and electronic properties of the hydrogenated amorphous germanium-carbon alloy system

Abstract

Abstract Hydrogenated amorphous germanium-carbon alloy (a-Ge1-xCx: H) films have been prepared by magnetron sputtering of a Ge target in an argon hydrogen methane atmosphere. The carbon fraction x, determined by secondary neutrals mass spectrometry, depended linearly on methane pressure and was in the range of × 10−4 ⩽ x ⩽ 0-4. The film properties do not show significant influence of carbonation until x reaches 0-03. The main absorptions features in the infrared spectra are related to Ge-C, Ge-H and C-H vibration modes and their dependence on x is reported. Carbonation widens up the optical Tauc gap from 1.0 to 1.3 eV. Other characteristic optical energies, the E04 gap, the single oscillator and dispersion energy are correlated to the Tauc gap. Carbonation increases the disorder of the material as evident from the decrease of the Tauc slope ✓B and the increase of the Urbach energy Eu form a minimum of 45 meV to more than 140 meV. The photoconductivity of the films decreases exponentially with Eu from 3 × 10–5 to 10–9(Ωcm)-1. Carbonation changes the relative position of the Fermi level within the gap of the alloys.