Bias-Enhanced Growth of NanoCarbon Interlayers Towards Ohmic n-Type Diamond Contacts

Ohmic metal contacts to n-type diamond have historically posed a challenge to the fabrication of diamond devices, due to the formation of a pervasive and rectifying Schottky barrier, which limits the practicality and scope of diamond devices. Nitrogen-doped nanostructured Carbon (nanoCarbon) films have recently been explored as ohmic interface layers, to enable low-resistance ohmic contact with n-type diamond. In this work, control over morphological and electrical properties of ohmic nanoCarbon films is achieved by altering the film growth time and utilizing a negative substrate bias. The films were characterized via TEM, which indicate the composition of the films consist of ~4 nm diameter sp3–bonded diamond grains surrounded by a matrix of sp2 bonded carbon. Monochromatic UV photoemission reveals occupied electronic states in the diamond gap for all growth conditions. The resistivity is determined via Hall effect to logarithmically decrease with bias from 1.7 Ω*cm, to 2.9*10-1 Ω*cm, and 3.1*10-2 Ω*cm, for films grown with 0V, 150V and 300V of bias, respectively. The carbon bonding order within each film is additionally characterized via Raman spectroscopy, for which the Raman sp2 “G” peak position increases with both growth time and bias voltage. A correlation is observed between the Raman sp2 “G” peak position and film resistivity on a logarithmic scale, thus the carbon sp2 bonding order is found to be a critical material parameter which alters the electrical properties of nanoCarbon films.