Cathodoluminescence measurements on heavily boron doped homoepitaxial diamond films and their interfaces with their Ib substrates

Heavily boron doped 1.8 to 2.4 mu m thick homoepitaxial diamond films with 1.5 x 10(21) cm(-3) <= [B] <= 1.75 x 10(21) cm(-3) have been deposited directly on their (100) lb substrates at 830 degrees C. Their cathodoluminescence spectra probe the controlled thicknesses from 0.28 to 2.8 mu m, therefore the bulk of the films as well as their interfaces with their substrates. The bulk of these films exhibit a band with shoulders ascribed to BETO (5.036 eV), FETO (5.094 eV) and BENP (5.184 eV) excitons whose energies are downward shifted by about 180 meV in comparison with monocrystalline diamond with low [B] < 5 x 10(18) cm(-3). This large shift allows the appearance of narrow peaks around 5.216, 5.271 and 5.357 eV ascribed to BETO, FETO and BENP from interfacial layers with low [B]. From their BETO to FETO ratio, their concentration of boron on isolated substitutional sites is significantly lower than their total low [B] content measured by SIMS. A tentative model is proposed to explain the characteristics of these 40 to 160 quasihomogeneous interfacial layers.