Analysis of x-ray photoelectron spectroscopy data of phosphorous doped carbon films deposited by pulsed laser ablation

Abstract

X-ray photoelectron spectroscopy (XPS) data obtained experimentally on phosphorous doped carbon films are analyzed using a specialized free software XPSPEAK 4. I to find out the atomic structure of doped carbon films. The carbon films were grown by pulsed laser deposition technique on p-type silicon using camphoric carbon target containing 0%, 1%, 3%, 5% and 7% of phosphorous by mass. The spectra for the whole energy range show the presence of carbon (C), phosphorous (P) and oxygen (0) in the grown films. Atomic percentage (at. %) of P content in the film varies approximately linearly with the phosphorous content in the target by mass. The analysis of the spectra for CIs, P 2p and 0 Is regions is performed after providing appropriate background subtraction to account for inelastic scattering and other energy loss processes. Curve fitting technique using Gaussian-Lorentzian lineshapes is used in Cis, P 2p and 0 Is regions of the spectra to isolate the presence of different elements and compounds in the grown films. Also to find the chemical structure at various depths of the film, the spectra in CIs, P 2p and 0 Is regions of argon ion etched carbon films are analyzed. The analysis of CIs region shows the presence of Sp2 and Sp3hybridized carbon and a Sp2 satellite peak due to x-x* shake up. The Sp2content is seen to remain almost constant for the films grown from target containing different amount of P. The FWHM of C-C Sp2 peak increases up to 5% P but decreases for 7% P probably due to clustering of Sp2chains and this clustering in Sp2phase probably decreases the bandgap for 7% P film. The P 2p region shows the presence of isolated phosphorous, P-C (C Sp2hybridized), P-C (C sp3 hybridized) and P-O bonds. The 0 Is region shows the presence of C-O and P-O bonds. The difference in peak position between the P-C (C Sp2) and P-C (C Sp3) peaks is found to be around 3 eV, though in the carbon region it is around 1 eV. The amount of phosphorous in P-C bond is seen to be much greater than donor concentration. A large amount of phosphorous in P-C bonds go into nondoping configurations and even some of the donors from doping configurations are used to convert the paramagnetic defects into diamagnetic. From the analysis of titted spectra in C, P and 0 regions and correlating the peak parameters for all the peaks, a simplified overall atomic structure of the phosphorous doped carbon film has been suggested containing Sp2 and Sp3 hybridized carbon, P-C bond (in both Sp2 and Sp3 network), P-O bond and C-O bond. Carbon film parameters like intrinsic carrier concentration, donor concentration, conductivity, minority carrier mobility and minority carrier diffusion length have been correlated with findings in the XPS analysis.