Electron emission from N-doped diamond doped with dimethylurea

Abstract

Cold cathodes are an essential element of vacuum nano electronics. Although cold cathode materials are usually either high melting point metals or silicon, diamond can be an alternative due to its negative electron affinity. In addition, diamond cathodes are advantageous to other materials because of its low extraction voltage and low power consumption. Moreover, the high physical and chemical stability makes diamond cathodes possible to implement electron emission in low vacuum of 0 -3 Pa.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 :00, :000, and :0000 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 000 ppm, 00 ppm and 0 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 0 -Pa. Anode-cathode distance is fixed to 50 m and the current versus voltage (I-V) characteristics are measured. Fig. shows the measurement circuit. As a result, the threshold voltage, which in this study is defined as the anode voltage when 0 -9 A was detected, is confirmed to be approximately 480 V for 000 ppm, 080 V for 00 ppm, and 00 V for 0 ppm diamond sample. Figure 2 shows the threshold voltage (V) for each anode-cathode distance (d) on all samples. It was found that most of the applied voltages drop in vacuum, as observed in the case of B-doped diamond [2]. Obtained V-d characteristics have different feature from heavily N-doped diamond with urea [3]. The slopes of all plots are almost straight when anode-cathode distances are over 0 m. The slope P2-B04 249 978--4244-3588-3/09/$25.00©2009 IEEE Techinical Digest of IVNC2009