Dependence of the electron affinity of homoepitaxially grown CVD diamond on the amount of surface oxygen

Abstract

Photoemission threshold energies have been measured for boron-doped homoepitaxially grown chemical-vapor-deposited (CVD) diamond with various degrees of the surface oxidation below 0.5 diamond (100) monolayer, or 7.8×10 14 O atoms/cm 2. In the case of the smooth surfaces, the observed threshold energy almost linearly increases with increasing amounts of chemisorbed oxygen atoms at low oxygen coverages below 0.1 monolayer and is followed by a saturation phenomenon. This behavior can be explained in terms of the Topping model, where the dipole–dipole interaction is taken into account and becomes more important at high dipole densities to reduce the increases in the work function, therefore, in the electron affinity of the diamond. On the other hand, in the case of substantial nonuniform oxidation due to the presence of significant amounts of particles abnormally grown, the threshold energy is almost unchanged at ∼5.4 eV for oxygen coverages below 0.3 monolayer, indicating the threshold energy is determined by surface area with low work functions or low electron affinities. The dipole-induced surface potential is discussed in relation to the changes in the electron affinity.