Electronic transport and optical properties of proton-implanted amorphous 2CdO center dot GeO2 films

Films of amorphous 2CdO . GeO2 with the band gap of 3.4 eV were prepared by rf sputtering. Protons were implanted into the films at doses 2 x 10(14)-2 x 10(16) cm(-2). On going from 2 x 10(14) to 2 x 10(16) cm(-2), de conduct ivity at 300 K increased from similar to 10(-9) to similar to 10(1) S cm(-1 ) and its activation energy fell from similar to 1 eV to almost zero (degen erate state). This result indicates that the Fermi level of this amorphous material may be controlled by proton implantation. The sign of Hall and See beck coefficients were negative, showing n-type electrical conduction and n o pn sign anomaly in Hall voltages. The Hall mobility was of the order of 1 0 cm(2) V-1 s(-1) (even at carrier concentration of similar to 3 x 10(19) c m(-3)), which is larger by several orders of magnitude than that of existin g amorphous semiconductors. No degradation of visible transparency was obse rved in all implanted samples. The optical conductivity may be described by the classical Drude formula with a single relaxation time, 2.7 x 10(-15) s . X-ray radial distribution function revealed that the local structure arou nd Cd2+ (coordination number; similar to 6) and Ge4+ (similar to 4) in the amorphous state is close to that of crystalline Cd2GeO4 and the amorphous s tate has a distribution of Cd-O-Cd bond angles. We assume that the electron ic transport properties of the present material primarily originate from th e extended conduction bands composed of Cd 5s orbitals. (C) 2000 Elsevier S cience B.V. All rights reserved.