The Electrical Properties And N-Type Conductive Mechanismof Oxygen Ion Implanted Ultrananocrystalline Diamond

Diamond is a very attractive material for electronic applications owing to its excellent physical and electrical properties, such as high hardness, high surface stability, high electron mobility, large energy gap, and so on. The diamond p-n junction is the key challenge to prepare diamond-based electronic devices. It is well known that diamond doped by boron exhibits good p-type conductivity, while it is very difficult to prepare high-quality n-type diamond. Ultrananocrystalline diamond (UNCD) films generally consist of nano-sized diamond grains with the size of3-5nm and amorphous carbon grain boundaries (GBs), in which significant π bonding governs the majority of the electrical conductivity. In this paper, hot filament chemical vapor deposited (HFCVD)’UNCD films were implanted by lower dose of O+, C+and annealed subsequently. The impacts of ion implantation and annealing temperature on the electrical and microstructural properties of UNCD films (were systematically studied. This work has important implications in the preparation of high-quality diamond based electronic devices. The1012cm-2O+-implanted UNCD films were annealed at different temperatures (500～1000℃). The UNCD films were implanted by O+with the doses of1011-1013cm-2and annealed at900℃. It is shown that the UNCD films exhibit p-type conductivity when the annealing temperatures (Ta) were in the range of500～725℃. There is a conductivity transition from p-type to n-type with Ta attaining to800℃and the Hall mobility dramatically increases to126-303cm2V-1s-1when Ta increases to900℃. The UNCD films with the surface dominantly terminated by hydrogen exhibit p-type conductivity. The appearance of π bonds on the surface of UNCD films with Ta increasing to800℃is related to n-type conductivity. After900℃annealing, H dramatically diffuses from the surface and a stronger oxidization occurs, which increases the amount of diamond phase in the surface of UNCD films and the increased dangle bonds in the surface of diamond grains are terminated by oxygen atoms. In this case, the amounts of π bonds and carbon-oxygen bonds in the surface of UNCD films significantly increases, which prefers to improve the Hall mobility of O+-implanted UNCD films. Moreover, the defects induced by ion implantation also give contributions to improve n-type conductivity in UNCD films. It is suggested that oxygen ion implanted diamond grains, oxidization and π bonds give contributions to high mobility n-type conductivity of UNCD films. The1012cm-2C+-implanted UNCD films were annealed at different temperatures (500～1000℃). The results show that the UNCD films transit from p-type to n-type conductivity with Ta attaining to800℃and the Hall mobility dramatically increases to159cm2V-1s-1when Ta increases to900℃. The p-type conductivity increases and the n-type conductivity decreases with the content of C-H bonds increasing.The high and low doses of O+implanted UNCD films were prepared by plasma immersion ion implantation technique and annealed at900℃. It is observed that low doses O+-implanted UNCD films annealed at900℃exhibit n-type conductivity, and its Hall mobility reaches183cm2V-1s-1, while high doses O+-implanted UNCD films annealed at900℃exhibit p-type conductivity. The increasing of the amount of sp3carbon and π bonds prefers to improve the n-type conductivity of the samples.