The Effect of Boron Doping Level on The Morphology and Structure of Ultra/Nanocrystalline Diamond Films

Abstract

AbstractIn this work, boron‐doped nanocrystalline diamond (BDND) films are grown on silicon substrates by hot‐filament (HF)CVD in Ar/H2/CH4 gas mixtures. In this study, the transition from ultra‐nanocrystalline to nanocrystalline diamond films is clearly shown by the addition of boron dopant to the growth of the gas mixture. The doping process consists of an additional H2 line passing through a bubbler containing B2O3 dissolved in methanol with various B/C ratios. Five sample sets are obtained with doping in the methanol bubbler solution of 2 000, 5 000, 10 000, 20 000, and 30 000 ppm for a 16 h growth time. The morphology, roughness, and structure of these films have markedly different properties. The cross‐section of the films is characterized by scanning electron microscopy (SEM) showing the transition from ultra‐nanocrystalline growth (renucleation process) to a columnar structure of nanocrystalline films. The acceptor density values, evaluated by Raman spectra and by Mott‐Schottky plot analysis, vary from 1020 to 1021 B cm−3 as the doping level increases. The grain size and the relative intensity of the (111)/(220) peaks are obtained from X‐ray diffraction (XRD) patterns of the films. The diamond average grain size increases from 10 to 35 nm for films with 2 000 and 30 000 ppm B/C, respectively, in the methanol bubbler solution. The preferential orientation also changes, from (220) to (111), as the boron doping level increases.