Field emission from as grown and nitrogen incorporated tetrahedral amorphous carbon/silicon heterojunctions grown using a pulsed filtered cathodic vacuum arc technique

Abstract

This article reports the field emission measurements on as grown tetrahedral amorphous carbon ͑ta-C͒ and nitrogen incorporated tetrahedral amorphous carbon ͑ta-C: N͒ films grown using a pulsed filtered cathodic vacuum arc technique. The effect of varying thickness on field emission in the as grown ta-C films and the effect of varying nitrogen content in ta-C: N films have also been studied. The values of threshold field of emission ͑E turn on ͒ increase with decrease of thickness in the as grown ta-C films. Nitrogen incorporation up to 5.2 at. % in ta-C films decreases the value of E turn on from 9.9 to 5.1 V / m and thereafter it starts increasing again. To understand the mechanism of electron emission, a realistic energy band diagram of ta-C : N / n ++ Si heterojunction has been proposed from the experimentally measured valence and conduction band offsets, using in situ x-ray photoelectron spectroscopy and optical spectroscopy data already published in DRM 9 ͑2000͒ 1148. The data are explained using the Fowler and Nordheim theory. The field emission results obtained reveal that there exists a barrier to emission and the main barrier is at the front surface and this is related to the conduction band offset of the ta-C : N / n ++ Si heterojunction.

Effect of high substrate bias and hydrogen and nitrogen incorporation on density of states and field-emission threshold in tetrahedral amorphous carbon films

“…58 These values are larger to those reported for similar material by Satyanaryana et al, 36 or for nitrogen-containing carbon films reported by Amaratunga and Silva, 48 Weber et al, 49 and Panwar et al 37 grown under different process conditions. A space-charge-induced band bending and hot-electron transport model was proposed by Amaratunga and Silva 48 to explain low electron field-emission from a-C:H:N thin films.…”

“…They achieved current densities up to 0.6 mA/ cm 2 at an electric field of 5.8 V / m. However, the values of E turn-on obtained in these ta-C:N films deposited with different N contents in the present study are larger than the values of E turn-on obtained by Satyanarayana et al 36 in ta-C:N films deposited at 80-100 eV ion energy using the L-bend FCVA process. The values of current density obtained in these ta-C:N films are larger than the values of current density obtained by Satyanarayana et al 36 and Panwar et al, 37 grown by a pulsed FCVA technique with an L-bend magnetic filter. Figure 9 shows the three-dimensional AFM image of ta-C:N films deposited with 12.7 at.…”

“…The focusing of the electric field on the negative charges results in downward band bending, allowing electron emission via the FN process, 35 without exceeding the thermal breakdown field. Panwar et al, 37 while reporting field-emission measurements on as-grown ta-C and nitrogen-incorporated ta-C films grown by a pulsed FCVA technique with L-bend magnetic filter, stated that using a realistic energy-band diagram proposed for ta-C: N / n ++ Si heterojunction, a barrier exists to the emission. They further observed that the main barrier lies at the front surface, which is related to the conduction-band offset.…”

“…These values are obviously quite low, and the true barrier may be much larger. 37 If we take a work function ͑͒ of 5 eV, typical of graphite bonding, then the FN slopes correspond to the field-enhancement factor ␤ of 226-366 for these as-grown ta-C films. We understand that ␤, in the case of a parallelplate arrangement and flat cathodes, is not a realistic estimation because emission is from discrete points.…”

“…However, we wanted to see whether the estimated parameter, even though not accurate, correlates to some other calculated value or shows a consistent trend with a change in material properties with a change in process parameters. To understand the mechanism of electron emission, a realistic energy-band diagram of ta-C: N / n ++ Si heterojunctions was proposed recently 37 from the experimentally measured valence-and conduction-band offsets, using in situ XPS and optical spectroscopy data. The values of of ta-C and ta-C:N films evaluated from this study are in the range of 3.95-4.55 eV.…”