Avoiding low temperature thermal donors in CMOS : E. Gordon Wright. Semiconductor int., 134 (September 1988)

Abstract

Specimens of graphite from limiter tiles in JET were implanted at room temperature with HT+ and DT+ ions at energies in the range 10–50 keV and at fluences between 5 ×1014and 3 × 1016ions/cm2, using the isotope separator. Depth profiles of tritium were measured by the T(d, α)n reaction using glancing incidence of the incoming 500 keV D+2 ions and detecting the outgoing α particles in a forward direction. Considerable broadening of the experimentally obtained depth profiles was observed as compared to calculated ones. For a specimen implanted with 5 ×1015HT+ions/cm2 at 40 keV, the depth profiles of tritium were studied as a function of isochronal annealing in vacuum up to ~1700 K. It was found that the release of tritium proceeds essentially without any change in the depth profile. Implanted tritium starts to be detrapped around 600 K, reaches a maximum in its release rate at 1100–1400 K and is 95% released at 1600 K. The obtained release curve is consistent with that obtained by other investigators for deuterium implanted at fluences of ~1016–1017 D+ ions/cm2, and it is shifted to ~ 200–300 K higher temperatures compared to the case of ~ 1018–1019/cm2 deuterium fluences. The observed behaviour is believed to be indicative of a single-step detrapping and recombination mechanism of implanted tritium ions, and its subsequent fast transgranular diffusion as molecules.