Masato Imai

In situ X-ray topographic study of the dislocation mobility in high-purity and impurity-doped silicon crystals

Abstract An in situ X-ray topographic technique using a high-power X-ray generator has been used to study the dislocation mobility at elevated temperatures in the stress range 1·2-40 MN m−2 for pure and impurity-doped silicon crystals. The variation of velocity with stress for both 60° and screw dislocations in high-purity crystal is linear throughout the whole stress range investigated, the activation energies for motion being independent of stress. No previously published theoretical models are able to account for the measured velocities quantitatively. Effects of impurities, such as oxygen, carbon, nitrogen, phosphorus and boron, are investigated in detail. Generally, the impurities bring about a deviation from linearity of the variation of velocity with stress under low stresses. Dislocations originally moving in impure crystals are immobilized when the stress becomes lower than a critical value. These phenomena are interpreted in terms of the development of an impurity atmosphere around slowly moving...

Effects of nitrogen on dislocation behavior and mechanical strength in silicon crystals

The characteristics of dislocation behavior and mechanical strength in tensile tests are investigated on the silicon crystals that are doped with nitrogen at the time of crystal growth by the floating‐zone technique. These are compared with those in the usual floating‐zone‐grown silicon crystals. Nitrogen atoms dispersed in a silicon crystal are shown to have no influence on the velocities of dislocations in motion in the temperature range above 600u2009°C. Dislocations in the nitrogen‐doped crystal are, however, immobilized while the crystal is kept under a low or zero applied stress at elevated temperatures. Like Czochralski‐grown silicon, nitrogen‐doped silicon shows a much higher yield strength than usual floating‐zone‐grown silicon when crystals are dislocated. It is concluded that interstitial nitrogen atoms bring about the hardening of silicon crystals through locking of dislocations upon congregating on the latter.

Investigation on higher order bands in irradiated Czochralski silicon

Using Fourier transform infrared absorption spectroscopy and Hall‐effect measurements we have investigated the higher order bands (HOB) in the fast neutron irradiated Czochralski silicon. Introducing the thermal donors (TD) to alter the Fermi level, the defect level giving rise to the HOB is analyzed, which is proposed to be located slightly below the TD(+/++) level. Furthermore, the observation for the characteristics of the photoexcitation and decay of both the HOB and the TD+ supports the assumption that this characteristic of the HOB is associated with a slow relaxation of photoexcited carriers.

Interaction of dislocations with impurities in silicon crystals studied by in situ X-ray topography

Abstract The characteristics of dislocation locking due to the development of an impurity atmosphere have been investigated by the in situ X-ray topographic technique for silicon crystals doped with various types of impurities. Oxygen, nitrogen and phosphorus atoms are found to be effective in locking dislocations while carbon atoms are not. The dependence of the locking behaviour on the impurity concentration is investigated in detail for oxygen-doped crystals. It is known that the magnitude of the locking force is determined uniquely by the number of impurity atoms congregated on a unit length of dislocations if the species and concentration of the impurity atoms in the crystal are specified. Individual nitrogen atoms exhibit the strongest locking effect among the impurity atoms investigated. However, locking proceeds most pronouncedly in oxygen-doped crystals owing to a high diffusion rate and a higher solubility of oxygen atoms in silicon. The origins of the strong locking effects of various impurity ...

X‐ray topography of growth striations in Czochralski‐grown Si wafers

Growth striations in Czochralski‐grown Si wafers have been observed by a scanning x‐ray double‐crystal method. We confirmed that the striations on the topographs relate to the variation of oxygen concentration.

SOLUTION EFFECTS ON THE MECHANICAL BEHAVIOUR AND THE DISLOCATION MOBILITY IN SILICON CRYSTALS

Effects of interstitial oxygen atoms and substitutional phosphor atoms on the dislocation mobility and the mechanical behaviour in silicon crystals are investigated. Dissolved oxygen atoms do not affect the velocities of dislocations in the temperature range investigated, but develop atmospheres around slowly moving and static dislocations and lock them firmly. The locked dislocations lose the function of the multiplication centers and the mechanical behaviour of the crystals becomes similar to that of nearly dislocation-free crystals. Phosphor atoms increase the mobility of dislocations but have no appreciable locking effect. The behaviour of the effective stress, and, thus, the state of the collective motion of dislocations in the steady state of deformation both with and without the presence of the solute atoms are correctly described by the hypothesis of Sumino.

On temperature dependence of the optically active behavior of an infrared active defect in silicon

Optically active behaviors of the infrared active defect, so‐called higher order bands, have been investigated at different temperatures in fast neutron irradiated silicon. It is found that the optically active decay follows logarithmic time dependence with a decay time of about 105 s, which is nearly temperature independent below 80 K. The residual absorption remains up to heating temperatures of 180 K. The experimental findings are discussed in terms of the relaxation characteristic of photoexcited carriers governed by neutron irradiation induced defect clusters.

Optical active process of higher order bands in fast neutron irradiated silicon

Abstract Using Fourier transform infrared absorption measurement with excitation at low temperatures, we have investigated the optical active process involving higher order bands (HOB) in fast neutron irradiated float-zone silicon. It is found experimentally that the photoexcitation and decay process of the HOB as well as the saturation value of the absorption intensity are in good agreement with the predictions of the macroscopic barrier model for the slow relaxation of photoexcited carriers caused mainly by defect clusters.