Search

Structural and electrical conduction properties of nitrogen-doped nanocrystalline diamond films are studied as a function of deposition temperature (TD) in a microwave Ar-rich/CH4 plasma with 30%N2 addition. Hall- and Seebeck-effect measurements confirm n-type conduction for TD above 1100 K. For TD from 1100 and 1220 K, the electron concentration increases up to 1020 cm-3 and the electron mobility is in the range of 4–8 cm2 V-1 s-1. For TD above 1250 K, the mobility decreases to ∼1 cm2 V-1 s-1. Low conductivity films deposited at low TD exhibit semiconductorlike thermal activation in the Arrhenius plots, while high conductivity films deposited at high TD are almost temperature independent, indicative of quasimetallic conduction. The nitrogen concentration in the films is about 0.3 at. %, independent of TD. As TD is increased, the sp2 content and order increase. This is responsible for the appearance of midgap states, their delocalization, and the larger distance between diamond grains. The high conductivity at high TD is due to the amount and crystallinity of sp2 carbon, rather than the nitrogen concentration. [ABSTRACT FROM AUTHOR]

Carrier transport mechanism in n-type nanocrystalline diamond (NCD)/p-type Si heterojunction diodes prepared by microwave plasma-enhanced chemical vapor deposition is studied in a temperature range of room temperature to 473 K. Current-voltage measurements show at most three orders of magnitude of rectification at ±20 V of biasing and room temperature, depending upon the deposition temperature. The current-voltage characteristics are described with the high ideality factor and the low current injection barrier due to the disordered NCD/Si heterojunction interface, mainly associated with grain boundaries in the NCD film. The Arrhenius plots of the currents reveal that the thermal excitation of carriers limits the conduction, and the apparent activation energy decreases drastically upon the bias voltage change from reverse to forward. The current injection mechanism at the interface is explained along the predicted energy-band diagrams, such that the major carriers from the defect states of the NCD are injected into the conduction band of the Si by forward biasing. [ABSTRACT FROM AUTHOR]