Fabrication of n-doped ultrananocrystalline diamond films for UV sensor applications

• Main Authors: Wei-Yuan Kuo, 郭為元
• Other Authors: Chii-Ruey Lin
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/86dep4

碩士 === 國立臺北科技大學 === 製造科技研究所 === 102 === Diamonds are considered as an ultimate material due to their own large energy gap and unique physicochemistry characteristics. Microcrystalline diamond (MCD) films, synthesized by conventional chemical vapour deposition (CVD) processes, however, possess high surface roughness due to their facet morphology. Also, this process are not readily available for doping activities, and thus hindering the potential uses of MCD films in semiconductor engineering fields. One way of synthesizing nanocrystalline/ultrananocrystalline diamond (NCD/UNCD) films is well-regarded as the effective method for resolving those restrictions. In this study, we propose here a method to synthesize ultrananocrystalline diamond (UNCD) using a home-made microwave plasma jet chemical vapour deposition (MPJCVD). Aiming at improvement of the electrical properties, nitrogen doping were conducted during the synthesis process for UNCD:N films. The effects of methane concentration, working pressure, and nitrogen incorporation on characteristics of the UNCD and UNCD:N films were investigated. In addition, the ultraviolet (UV) detection performance of the as-synthesized UNCD:N films were studied. In the synthesis of UNCD films, it was shown that increase in CH4 concentration induced the nanonization of diamond grains from microcrsytalline to ultrananocrystalline structure. The diamond growth by MPJCVD system was found to have high plasma density and ensure high activity species at low microwave power, thus led to ultra-smooth surface and ultrananocrystalline diamond grains of the as-synthesized films. As incorporated with nitrogen during the UNCD synthesis process, significant changes in microstructure, surface roughness, electrical and optical properties were observed. The low nitrogen doping (1%) also resulted in preferred growth in (100) orientation of diamond grains and needle-like shape in morphology of the UNCD:N films. In other stage of this study, the as-synthesized UNCD:N films were employed as absorption layer for UV detection application. The effects of microstructure and nitrogen incorporation on UV detection performance were studied. The UNCD:N film with needle-shape morphology possessed excellent photoconductivity which photo-dark current ratio achieved 2.89 orders with highly fast, stable, and reproducibility response to UV irradiation in air ambient. These good performance of the fabricated detector were due to the increase in UV irradiation absorption as results of a high surface-to-volume ratio of the UNCD:N films. Also, the obtained highly smooth surface and nitrogen incorporation of the films indeed ensured a relatively low dark current as well as good electrical characteristics of the fabricated UV detector. The above results demonstrated a prosperous applications of UNCD:N films in UV detection devices in the future.