MOCVD growth and characterization of cobalt phosphide thin films on InP substrates

Cobalt phosphide thin films were grown by metal-organic chemical vapor deposition (MOCVD) in H2 atmospheres on InP(001) substrates using bis(-methylcyclopentadienyl)Co(II) [Co(CpMe)2] and phophine (PH3) precursors at 550°C. Film microstructure, composition, and morphology were investigated in detail by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), and atomic force microscopy. Films were crystalline and consisted mainly of the orthorhombic CoP phase and some amount of the CoP2 phase. XPS measurements indicate an oxidation state (III) for Co, while the P/Co ratio was found by RBS to lie in the range 1-2. The coatings were highly textured with (202), (103) CoP, and (-311) CoP2 crystal planes parallel to the substrate surface. The root mean square surface roughness was below 10 A; for thicknesses smaller than 20 nm and increased to a maxiumum of 70 A; for a 35 nm thick film. Cobalt and In intermixing was investigated by XPS depyh profiles.