Modeling of the electron field emission process in polycrystalline diamond and diamond-like carbon thin films

Abstract

Electron field emission has been observed from carbon thin films at relatively low electric fields. These films range from amorphous carbon to polycrystalline diamond films. There are many models that attempt to account for the electron field emission process observed in these films. The initial models that were based on the emission due purely to a negative electron affinity have now been modified. The emission from diamond like carbon ͑DLC͒ films, although following a FowlerNordheim type curve, do not give realistic values for the emission areas or barriers purely based on a tunneling mechanism. Therefore, a model based on space charge band bending at the back junction is proposed to account for the electron emission at low electric fields from DLC. In this ''space charge interlayer'' model the real cathode is the substrate, from which hot electrons are created due to the fully depleted DLC film the electrons encounter before reaching the front surface of the film. In this article we extend the model to incorporate the emission of electrons from polycrystalline diamond thin films.

Electron emission from conduction band of diamond with negative electron affinity

“…The second is the triple junction emission reported by Geis in 1998 [16]. Theoretical interpretations of these experimental results were made by many researchers, reflecting the importance of these two reports [17][18][19][20]. To the best of the present authors' knowledge, all the other reports describe emission at higher threshold voltage/field, which implies that they can be categorised as Type (ii) or (iii).…”

Theory of Field Emission

“…The effective mass in a semiconductor is not, in general, equal to the electron rest mass in vacuum. The emitted current from wide band gap semiconductors can be strongly influenced or dictated by transport through the Schottky barrier characterizing the back contact, and transport through the wide band gap material has numerous complications of its own [61,[68][69][70][71]. Surface layers or adatoms [72], and for analogous reasons, layered semiconductor structures which can give rise to a resonant tunneling effect [73], complicate matters by introducing modifications to either the potential barrier or the supply function.…”

Enhanced electron field emission from preferentially oriented graphitic films

“…The turn on field ͑TOF͒ of carbon based materials was found to be influenced by different surface and bulk properties such as amount of dopants additives such as nitrogen, sp 2 to sp 3 material ratio, heat treatments, and surface termination. 5-7,10-12 Typical reported TOF values for different carbon materials are 5 -100 V / m for chemical vapor deposited polycrystalline diamond, [8][9][10][11][12][13][14] 3-50 V/m for DLC, 5,6,9 10-20 V / m for tetrahedral a-C ͑t : a-C͒, 7 3-5 V/m for t : a-C:N, 7 3-15 V/m for nanodiamond, 3,12 and 2-5 V/m for CNT. 2,4 Great interest has been focused on understanding the electron emission mechanisms of carbon based materials.…”

“…͓DOI: 10.1063/1.2422876͔ Electron field emission ͑EFE͒ characteristics of carbon based materials show great promise with regard to carbon based EFE applications. 1-3 The interest is focused on a variety of materials such as diamond, carbon nanotubes ͑CNTs͒, 2,4 and many other carbon complexes including the large variety of amorphous carbon 5-7 ͑a-C͒ and diamond like carbon 5,6,8,9 ͑DLC͒ materials. The turn on field ͑TOF͒ of carbon based materials was found to be influenced by different surface and bulk properties such as amount of dopants additives such as nitrogen, sp 2 to sp 3 material ratio, heat treatments, and surface termination.…”