Effect of material properties on low-energy electron transmission in thin chemical-vapor deposited diamond films

Abstract

Electron transmission spectroscopy is used to measure the electron escape depth in thin diamond films and to examine how the transport characteristics are affected by the crystal quality and B concentration. In the studies, energy distribution and yield measurements are taken from several films with thicknesses ranging from ∼1.5 to 4.2μm, and the data are characterized in both the conduction-band and grain-boundary transport regimes. In the conduction-band transport regime, the escape depth increases from 0.5 to 0.85 to 1.3μm as the film thickness increases from 1.5 to 2.0 to 2.5μm due to the higher crystal quality in the thicker diamond films. However, the escape depth is relatively insensitive to different B concentrations in films of similar thickness. On the other hand, the B concentration more strongly affects the transmission stability. At sufficiently high B concentration (⩾1020cm−3), the transmission yields and energy distributions are fairly insensitive to changes in Io. However, at lower B concentration, the measurements exhibit evidence of sample charging in spite of a reasonably long escape depth and high secondary (reflection) yields. In investigations of the grain-boundary transport regime, the transmission characteristics are found to be largely insensitive to the crystal quality or doping levels of the diamond films, with low yields and broad energy distributions observed in all of the measurements. Moreover, the yields and energy distributions vary little with beam energy or current, except for measurements from the thickest 4.2-μm film that exhibit irregular variation in intensity and energy.