C. Nobili

HELIUM-IMPLANTED SILICON : A STUDY OF BUBBLE PRECURSORS

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5×1015 cm−2, 20 keV, and liquid–nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV 15N2+ elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 °C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 °C) the traps are almost...

He-implantation induced defects in Si studied by slow positron annihilation spectroscopy

Open volume defect profiles have been obtained by performing Doppler broadening measurements with a slow positron beam on p-type Si samples implanted near liquid nitrogen temperature with He ions at 20 keV and at 5×1015 and 2×1016 cm−2 fluence. The evolution of the defect profiles was studied as a function of isothermal annealing at 250 °C. The fraction of released He was measured by thermal programmed desorption. The defects could be identified as a coexistence of monovacancies stabilized by He-related defects and divacancies. The number of defects decreases for annealing time of a few minutes, then increases at longer annealing times. The mean depth of the defect profiles in the as-implanted samples was found to be very near the surface. After annealing, the mean depth increases to less than one half of the projected He range. This complex dynamics has been interpreted as due to passivation of vacancies by He during the implantation process and the first annealing step when no appreciable He is lost, an...

Visible photoluminescence from He‐implanted silicon

Visible photoluminescence has been observed at cryogenic temperatures from crystalline Si bombarded with He and exposed to H either as plasma or gas in the 250–450 °C temperature range. The experimental results are consistent with the formation of Si nanoparticles produced by He segregation, which is responsible for exciton localization, and H passivation of the nonradiative recombination centers.

Visible luminescence from silicon by hydrogen implantation and annealing treatments

Luminescence at an energy higher than the Si band‐gap energy has been observed following H implantation and annealing treatments of Si samples. This phenomenon is discussed considering the damage caused by the H implantation and its evolution with thermal treatments. No definitive answer on the origin of the luminescence is given but various possible models are proposed.

Helium/deuterium coimplanted silicon: A thermal desorption spectrometry investigation

Thermal desorption spectrometry has been applied to investigate the blistering and exfoliation phenomena which occur at the surface of a p-type (100) silicon wafer coimplanted with helium and deuterium. During the heat treatments in linear temperature ramp, an explosive emission of both gases occurs. The phenomenon is kinetically controlled with an effective activation energy of 1.3±0.2 eV. In addition, the desorption spectra present a second contribution, attributed to deuterium emission from buried cavities. Also in this case, the process is kinetically controlled with an effective activation energy of 1.9±0.3 eV. Thermal desorption spectrometry is a suitable technique to have information about various phenomena which occur during blistering and exfoliation.