The influence of the waveform on the surface charging of a spacer stressed by impulse voltages is investigated in this paper. The experimental study was carried out using a simplified spacer with an adhering conducting particle under homogeneous conditions in SF 6 gas. A capacitive probe was specially designed to yield the surface charge data through potential measurement. The results show that the impulse waveform has a significant influence on charge accumulation on the spacer surface. Also, the measurements of the optical signal occurring in the predischarge process can give an explanation for the mechanism of charge accumulation on the spacer surface in the presence of impulse.

The effect of radiation damage on neutron-transmutation-doped silicon of initially low-and high-resistivity materials has been studied by electrical property measurements. The materials were irradiated with a moderate thermal (0.45-1.0~ 10" neutrons cm -') and fast (0.45-8.1 x 10"j neutrons cm"') neutron fluences. After irradiation, a small reduction of carrier mobility of the initially low-resistivity materials was observed, while the reduction of conductivity was large. The annealing behaviour and temperature dependence of mobility of the materials indicate that the mechanism of carrier scattering is dominated by ionised impurities acting as point defects. The conductivity of those materials was recovered after annealing at 560 "C for 60 min. In the range of annealing temperatures below 600 "C, the carrier mobility of initially high-resistivity materials decreased together with the conductivity. The last result can tentatively be explained by a defect cluster model for fastneutron-induced lattice damage.

The recombination lifetime of excess carriers in silicon epitaxial wafers (p/p- and n/n-) with substrates of high resistivity has been analyzed based on a continuity equation. The solutions are derived for two cases of lifetime values. Under the conditions that the wafer surfaces are chemically passivated, and that the effects of recombination velocity and built-in potential at the interface of the epitaxial/substrate layer can be neglected, an approximate expression of effective lifetime can be derived from the solutions of the continuity equation. The result indicates that the effective lifetime is not only a function of the bulk lifetimes in both the epitaxial layer and substrate, but also a function of their thicknesses. The results of analytical solutions are applied to a commercially available silicon p/p- epitaxial wafer. The difference between the experimental and analytical results is discussed.

Radiation damage in wafers cut from neutron transmutation doped floatzone silicon crystals has been studied by using minority carrier lifetime and conductivity measurements. The isochronal annealing behaviour of lifetime is characterised by three regions in the temperature range from 480 to 1160 OC. For the samples annealed in the temperature region I where the recovery of conductivity is not complete, a minority carrier trapping effect is clearly observed. The annealing temperature to remove the trapping effect depends on the fast-neutron fluence for pure Fz-Si, and it is above 700 O C for the neutron fluences of 9th = 5.5 x 1 0l8, 9'=5.5 x 10" n cm-'. In region 11, the recombination lifetime begins to increase after the conductivity reaches full recovery, and a light-sensitive effect in which the lifetime increases remarkably with the illumination of an additional photo-bias is observed. The effect is tentatively explained by a defect cluster model. In region Ill beyond 1000 O C , the light-sensitive effect disappears, and the lifetime sharply increases with annealing temperature. However, the annealing temperature required to remove this effect is influenced by not only fast-neutron irradiation or contamination in the starting materials but also by thermal-neutron fluence.

Radiation damage was studied by deep-level transient spectroscopy and Hall effect measurements for the neutron-transmutation-doped silicon of initially high-and low-resistivity (phosphorus-contained) materials. In the irradiated materials a total of twelve electron traps was observed. A large reduction of carrier concentration and a small reduction of carrier mobility were found in the initially low-resistivity samples ( c 1 2 R cm), correlated closely with the divacancy responsible for two traps ( E 4 and E8). For the initially highresistivity samples ( > 1000 R cm) results showed large reductions of carrier concentration and mobility; these reductions are closely correlated with electron traps E3, E5 and E10. It appeared that the latter three traps correspond to some energy levels within the fast-neutron-induced defect clusters. However, in the initially low-resistivity samples, t h e formation of these traps appeared to be controlled by initially doped phosphorus atoms. In other words, due to the difference in the annealing temperature of divacancy and defect cluster, the annealing-out temperatures of carrier concentration and mobility were lower for the initially low-resistivity samples in comparison with t h e initially highresistivity samples.