Effect of Different Heat Treatment Regimes on Electrical Properties and Microstructure of n-Si

The features of changes in the electrical properties and microstructure of n-type silicon single crystals, doped with phosphorus by different methods (through the melt and by the nuclear transmutation method) are revealed, depending on the heat treatment conditions, which are widely used in research with semiconductors and when creating devices based on them. The nuclear transmutation method is based on the transformations of silicon isotopes when they capture thermal neutrons. The principal difference of the transmutation doping from the metallurgical doping method is that dopants are not introduced into the initial material from the outside, but are formed during the irradiation process directly from the atoms of the doped material. Using transmutation doping, one can obtain a high homogeneity of the distribution of impurities, which is ensured by the random distribution of isotopes, neutron flux uniformity and small neutron capture cross sections, as well as one can obtain the high accuracy of doping due to proportionality of the concentration of introduced impurities (at the constant neutron flux) to the irradiation time. It was established that the degree of defectiveness of the n-Si annealed crystals, controlled by selective chemical etching and X-ray topography, depends not only on the time of high-temperature annealing, but also on the cooling rate of the samples from the annealing temperature to room temperature. It was revealed that the long-term high-temperature annealing of silicon samples, regardless of the phosphorus doping method, promotes the generation of deep donor centers, both at slow and fast cooling, and reduces the charge carrier concentration in the samples, doped through the melt, by 1.5-2 times, in the transmutation-doped ones by 1.5-3.5 times, and in the latter case the effect is more pronounced upon fast cooling.