VIBRATIONAL, OPTICAL AND ELECTRONIC-PROPERTIES OF THE HYDROGENATED AMORPHOUS GERMANIUM-CARBON ALLOY SYSTEM

Hydrogenated amorphous germanium-carbon alloy (a-Ge1-xCx:H) films have been prepared by magnetron sputtering of a Ge target in an argon hydr ogen methane atmosphere. The carbon fraction x, determined by secondar y neutrals mass spectrometry, depended linearly on methane pressure an d was in the range of 3x10(-4)less than or equal to x less than or equ al to 0.4. The film properties do not show significant influence of ca rbonation until x reaches 0.03. The main absorptions features in the i nfrared 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, th e E(04) gap, the single oscillator and dispersion energy are correlate d to the Tauc gap. Carbonation increases the disorder of the material as evident from the decrease of the Tauc slope root B and the increase of the Urbach energy E(U) form a mininium of 45 meV to more than 140 meV. The photoconductivity of the films decreases exponentially with E (U) from 3x10(-5) to 10(-9)(Ohm cm)(-1). Carbonation changes the relat ive position of the Fermi level within the gap of the alloys.