Characterization of homoepitaxial and heteroepitaxial diamond films grown by chemical vapor deposition

Sulphur-doped and boron-sulphur co-doped diamond thin films were prepared by using chemical vapour deposition on p-type Si (100) and HTHP-diamond (100) substrates. The structures and properties of CVD diamond films were investigated with atom force microscope (AFM), Raman spectrum, sanning tunneling microscopy (STM) and current imaging tunneling current spectroscopy (CITS). Comparing the structures and properties of the doped diamond films grown on Si and HTHP diamond substrates, we find that the films deposited on Si substrates are composed of spherical grains with size of one hundred nanometer, the doped diamond films on Si substrates consist of large grains with a high fraction of grain boundaries due to the successive secondary nucleation,and the roughness of the films is estimated to be around 18.5nm. The doped diamond films on HTHP diamond substrates are composed of nanometer crystal grains with the sizes of 10—50nm and the film surface is flat with the roughness estimated to be around 1.8nm. Raman and resistivity measurements reveal that the films deposited on HTHP diamond substrates have much higher quality, fewer defects and lower stress, and higher conductivity than the films grown on Si substrates. Current imaging tunnelling current spectroscopy (CITS) images indicate that some grain boundaries and crystalline facets near the grain boundaries are he high electron emission regions. However, the grain boundaries and crystalline facets of the doped diamond films on HTHP diamond substrates have uniform electron emission currents, which indicates that the doped atoms are uniformly distributed in that films. The local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate the n-type conduction.