Growth of ideal amorphous carbon films at low temperature by e-beam evaporation

Abstract

Amorphous carbon (a-C) films were prepared by e-beam evaporation on silicon substrates. The effects of substrate temperature between room temperature and 600 °C were mainly studied. Raman spectroscopy, scanning electron microscopy, atomic force microscopy, UV-Vis-NIR and Hall-effect measurements were used to characterize the structure, morphology, roughness, transmittance and conductivity of a-C films, respectively. The results indicated the films obtained by e-beam evaporation were all graphite-like carbon films. The films deposited at 200 °C with a thickness of 75 nm presented the best performance with I_D/I_G of 4.50, FWHM_G of 115.9 cm⁻¹, an optical gap of 0.6 eV, a roughness of 0.825 nm and an electrical resistivity of 3.60 × 10⁻³ Ω cm. As the thickness reduced to about 8 nm while remaining at the same substrate temperature, the films still exhibited good structural quality, continuity and conductivity. SEM images from Ge/a-C/Si stacks and Ge/Si stacks confirmed the necessity of a-C buffer layer for smooth Ge film growth. Raman analysis of Ge films indicated that the crystalline quality of Ge films obtained from Ge/Si stacks was improved by inserting an a-C layer. The mechanism of a-C films as buffer layers was further explored by X-ray diffraction. The results suggested that a-C films with good properties prepared at such low temperature may be used as buffer layers for growing high quality Ge or GaAs films on Si.