Effect of substrate materials on the electron field emission characteristics of chemical vapor deposited diamond films

Abstract

Substrate materials used for growing diamond films were observed to modify thin films’ electron field emission properties significantly. Using heavily doped silicon (LR-Si) as a substrate lowered the turn-on field from ${\mathrm{(E}}_0{)}_{\mathrm{Si}}\mathrm{=14.4\hspace{0.17em}V/\mu m}$ to ${\mathrm{(E}}_0{)}_{\mathrm{LR-Si}}\mathrm{=9.7\hspace{0.17em}V/\mu m}$ and increased the emission current density from ${\mathrm{(J}}_e{)}_{\mathrm{Si}}{\mathrm{=4\hspace{0.17em}\mu A/cm}}^{\mathrm{2}}$ to ${\mathrm{(J}}_e{)}_{\mathrm{LR-Si}}{\mathrm{=40\hspace{0.17em}\mu A/cm}}^{\mathrm{2}}$ (at 16 V/μm). However, electron field emission properties can be further improved only by using Au precoatings to modify the characteristics of interfacial layer. The turn-on field was lowered further to ${\mathrm{(E}}_0{)}_{\mathrm{Au–Si}}\mathrm{=8.7\hspace{0.17em}V/\mu m}$ and emission current density was increased further to ${\mathrm{(J}}_e{)}_{\mathrm{Au–Si}}{\mathrm{=400\hspace{0.17em}\mu A/cm}}^{\mathrm{2}}$ (at 16 V/μm). Secondary ion mass spectroscopic examination indicated that the main interaction is the outward diffusion of Au species into amorphous carbon layer, lowering the resistivity of this interfacial layer. The electrons can therefore be transported easily from Si substrate across the interfacial layer to the diamonds and subsequently field emitted.