Electronic properties of low-field-emitting ultrananocrystalline diamond films

This work reports on electronic properties of nitrogen‐doped, n‐type ultrananocrystalline diamond (UNCD) films grown on p‐type Si substrates from CH4–Ar–N2 gas mixtures using a microwave plasma chemical vapor deposition technique. Films ∼1 µm thick were grown with 5%N2 and 10%N2 in the plasmas. Charge‐based deep‐level transient spectroscopy showed a shallow level of point defects with an activation energy of ∼0.05 eV. The density of these shallow defects was increased with increasing nitrogen content in the plasma. Complex scanning probe microscopy methods were applied to study the film microstructure. Generally it was found that the nitrogen‐doped UNCD films showed a periodic ‘cell‐like’ structure in which the cell with a lateral size of several nanometers was less conducting than the boundary between the cells. The boundary width was found to be 0.5–1 nm. The observed details of the periodic structure can be associated with diamond nanocrystallites (grains) and grain boundaries, respectively. In addition, 2–5 nm high‐conducting inclusions clustered on the film surface were observed. It was noted that the emission field was inversely proportional to the film electroconductivity, and the lowest emission field of F ∼ 10 V µm−1 was detected near the high‐conducting inclusions. Moreover, the surface electron potential at the emission sites was lowered. The reasons why the shallow donor center is predominantly introduced by nitrogen incorporated into the grain boundaries and the possible mechanisms of low‐field electron emission from the nitrogen‐doped UNCD films have been discussed. Copyright © 2004 John Wiley & Sons, Ltd.