Electron emission from N-doped diamond doped with dimethylurea

We have been focusing on fabricating a photodetector that consists of a diamond cold cathode and an amorphous selenium (a-Se) photoconductor, which is one of the practical applications of a cold cathode. We have previously succeeded in achieving a proto-type photodetector of which a heavily nitrogen (N)-doped diamond was used as the cold cathode, and the results indeed showed a low operation voltage. This heavily N-doped diamond was fabricated using urea as a dopant and the saturated solution of urea and methanol was diluted with acetone and used as a reactant gas. Although this diamond cathode exhibited low extraction voltage, the reproducibility of obtaining low threshold cathode was not as high as expected and the improvement should be considered for wider extensive application. In order to solve this problem, dimethylurea was introduced due to its structure more similar to diamond and soluble in acetone, where urea is insoluble without the use of methanol. Dimethylurea-saturated solutions of acetone diluted at a ratio of 1:100, 1:1000, and 1:10000 with acetone is vaporized and used as the reactant gas and diamond is grown on a silicon substrate by hot filament CVD method. The N/C ratio in the CVD apparatus is 1000 ppm, 100 ppm and 10 ppm respectively. The electron emission characteristics of N-doped diamond doped with dimethylurea are then measured. The experiment was performed under a base pressure of 4 x 10^-6 Pa. Anode-cathode distance is fixed to 50mum and the current versus voltage (I-V) characteristics are measured.