Formation of ohmic contacts to p-type diamond using carbide forming metals

Publisher Website
Google Scholar
Abstract
The measurement of the specific contact resistance, ρC, and microstructural analysis at the metal/diamond interface were carried out for diamond with various acceptor concentrations, NA, in order to understand the carrier transport mechanism at the metal/diamond interface. The ρC measurements were carried out for polycrystalline boron‐doped semiconducting diamonds which were prepared by the microwave plasma chemical vapor deposition. The acceptor concentrations, estimated by the boron concentrations measured by secondary ion mass spectroscopy, ranged from 3×1018 to 3×1020 cm−3. Ti and Mo films, which form carbides with diamond, were deposited on the diamonds using the electron‐beam evaporation technique. The ρC values were measured by the circular transmission line method before and after annealing at temperatures in the range of 400–600 °C. The dependence of the ρC values on the acceptor concentrations suggested that the dominant transport mechanism was the field‐emission for the diamond with NA around 1020 cm−3 and the thermionic‐field‐emission for the diamond with NA from 3×1018 cm−3 to 4×1019 cm−3. The ρC values of the Ti contacts were observed to decrease upon annealing, whereas those of the Mo contacts decreased gradually with increasing annealing temperature. However, the ρC values of both the Ti and Mo contacts reached at the same value of ∼1×10−6 Ω cm2 after annealing at 600 °C for the diamonds with NA higher than 1020 cm−3. Note that the ρC values of the Mo contact were extremely stable at high temperatures: the ρC values did not deteriorate after annealing at 600 °C for more than 3 h. The thermally stable molybdenum carbide (α‐Mo2C) and amorphous layers were observed at the Mo/diamond interface after annealing at 600 °C by cross‐sectional transmission electron microscopy and x‐ray diffraction.