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We report resistivity measurements in the temperature range 0.15-1.2 K Performed on non-compensated Si:As samples doped by ion implantation on the insulating side of the metal-insulator transition. The data show a crossover of the variable-range-hopping (VRH) resistivity dependence rho(T) from rho is-proportional-to exp(T1/4/T)1/4 (Mott VRH predicted behaviour) to rho is-proportional-to exp(T1/2/T)1/2, which demonstrates the persistence of a Coulomb pp in the density of states even in the vicinity of the critical concentration. The simultaneous observation of the T1/4 and T1/2 parameters allows the determination of the effective size of the pp.

We present low-temperature resistivity measurements, carried out in the temperature range 100400 mK on uncompensated Si:P samples doped by ion implantation in the just-metallic side of the metal-insulator transition. As the dopant concentration increases the experimental data confirm the presence of the change of sign in the T -dependent correction to the conductivity, with a cusplike behavior of the critical prefactor. However, the sign transition is followed by the turning on of an anomalous temperature contribution. We analyze both features in terms of renormalization of electron-electron interaction effects and show that in Si:P the effective-electron-coupling constant has a sizable enhancement both with doping and temperature. © 1995 The American Physical Society.

The reaction between molybdenum thin films and single-crystal Si〈111〉 substrates was studied as a function of the concentrations of impurities (mainly oxygen) in the metal film. At a low oxygen concent (1–2 at.%), only the silicide phase MoSi 2 was observed, and a thickness proportional to the square root of time corresponding to an average activation energy of 3 eV in the temperature range 545–600 °C was found. During the formation of the silicide the oxygen originally present in the molybdenum films accumulates at the interface between the silicon and the MoSi 2 . In contrast, a higher oxygen content (4–5 at.%) prevents the formation of any silicide phases in the above temperature range and leads to the formation of MoSi 2 and Mo 5 Si 3 phases at temperatures near 800 °C. MoSi 2 was always observed at the inner interface with Mo 5 Si 3 on the surface. The oxygen segregates from the silicides and accumulates at the Si-MoSi 2 and MoSi 2 -Mo 5 Si 3 interfaces to form a non-uniform layer of SiO x ( x ⩽ 2).

A detailed experimental analysis of self-anneal and post-anneal phenomena in heavily arsenic-implanted silicon has clarified the role of the beam current in the ion implantation process. Current effects, which are more evident the higher the implant current, consist of an increase in temperature during the implant and lead to the formation of (1) a heavily damaged crystalline bulk layer, which cannot be further reconstructed by successive heat treatments performed at moderate temperature (lower than 800°C), and (2) a partially reconstructed surface layer, the quality of which can be increased by post-annealing treatments. Both carrier mobility and dopant activation are significantly reduced in the highly damaged bulk region.

Silicide formation is strongly affected by the presence of oxygen contained in the metal film. A study has been performed by heating at various times and temperatures samples constituted by a thin Pt film sputter deposited on a silicon substrate. Four different oxygen concentrations were implanted in the Pt film ranging from 1 to 0.1 at.%. The presence of oxygen slows down the growth rate of Pt2Si. At 315 °C in the sample with an oxygen concentration of 1 at.%, about 1000 A of Pt2Si are formed after 20 min of annealing. During the silicide formation, the oxygen originally contained in the platinum films segregates at the Pt2Si/Pt interface. This accumulation acts as a barrier for the transport of Pt and a new phase, PtSi, can form at the Pt2Si/Si interface. The dose necessary to stop the Pt2Si reaction is about (2–4)×1015 at./cm2 at 315 °C.

The heat capacities of three specially implanted silicon bolometers have been measured at low and, for the first time, at very low temperatures down to about 10 mK by exposing them to alpha-particles and X-rays. The lattice contribution shows a behaviour with temperature in good agreement with the Debye law, and the percentage of thermalized energy of the alpha-particle is found to be about 70%. The specific heat of the doped part, which dominates at very low temperatures, is not inconsistent with linearity, even if a dependence on a higher power of the temperature seems preferred. The parameter of linearity is found to be considerably larger than expected from extrapolation to very low temperatures of the existing results on silicon P-doped by diffusion.

Diffusion and segregation effects during the formation of silicides in the interaction of an Ni-Pt alloy with Si and Si substrates were investigated by means of 4He+ megaelectronvolt Rutherford backscattering spectrometry, Auger electron spectroscopy coupled with Ar+ ion sputtering and glancing angle X-ray diffraction as functions of the heat treatment (150–850°C). The Ni-Pt alloy film was deposited onto silicon by codeposition using a system of electron guns. After low temperature annealing of the sample the nickel segregates and NiSi is formed at the original silicon-alloy interface. Further annealing promotes the interdiffusion of platinum into the NiSi. The barrier heights measured on n-type silicon confirm these observations. At low temperatures or after short annealing times the barrier height is 0.70eV. Further annealing increases this value until saturation is reached at, for Pt45Ni55 alloy, 0.77 eV. At high temperatures the contact degrades.

Platinum diffusion in n‐type silicon has been measured using various kinds of spectroscopic techniques for deep energy levels. Platinum acts as an acceptor which captures electrons. An energy level of 0.23±0.02 eV was found for the trap. The diffusion profile can be explained, as in the case of gold, with a kick‐out mechanism involving silicon self‐interstitials. From the model, an activation energy of 5.01 eV for silicon self‐interstitial diffusion can be inferred.

Three new silicon bolometers have been constructed and exposed to alpha particles and X-rays at temperatures down to 10 mK in a dilution refrigerator. The low impedence of these detectors enabled us to achieve, together with energy resolutions comparable with those of similar counters, much faster pulse risetime. The flexibility of these bolometers allows measuring energies from a few keV to tens of MeV.

A new detector of ballistic phonons is presented. It is a P‐doped Si bolometer realized on top of a (100)Si crystal by ion implantation. The open circuit responsivity of the bolometer is 8000 V/W and the response time less than 50 ns. Time‐resolved spectra of ballistic phonons propagating in the same Si crystal along the 〈100〉 direction are reported.

The properties of carbon nanotubes (CNTs), the new allotropic status of carbon discovered in 1991, have been widely investigated in all possible application field. This new material in fact can be easily obtained chemically by CVD (Chemical Vapour Deposition) as a layer of nanotubes growth on a wide variety of materials. When growth on a silicon surface, CNTs create a semiconductor heterojunction with peculiar photoresponsivity properties. We studied this heterojunction with the purpose to realize a large photocathode with high quantum efficiency in a large wavelength range from UV to IR. Results obtained up to day allowed us to build a new kind of photodetector very cheap, stable and easy to manage. Recently this new device has been proposed as one of candidates for the beam monitor system of SuperB.

The realization of a Silicon Carbon Nanotube heterojuntion opens the door to a new generation of photodetectors (Si-CNT detector) based on the coupling between this two materials. In particular the growth of Multiwall Carbon Nanotubes on the surface of a n-doped silicon substrate results on a Schottky diode junction with precise rectifying characteristics. The obtained device presents a low dark current, high efficiency in the photoresponsivity, high linearity and a wide stability range. The junction barrier is about 3.5 V in reverse polarity with a breakdown limit at more than 100 V. The spectral behavior reflects the silicon spectral range with a maximum at about 880 nm.