A new neutron transmutation doping system for radial irradiation uniformity

Abstract

Nowadays, Neutron Transmutation Doping (NTD) of silicon ingots is successfully used to produce the n-type semiconductor. NTD’s main advantage, which is to say its uniform resistivity distribution, leads to semiconductor materials with fewer defects and, accordingly, better performance. Radial uniformity usually is achieved by rotating the ingot during irradiation. However, due to neutron attenuation, the neutron reaction rate in the ingot’s center region generally is lower than in the outer region. Such radial non-uniformity becomes severe when the diameter of the ingot is larger, or when materials with a high-neutron-reaction cross-section are used. In this study, a slit method to selectively shield neutrons that react with the ingot’s outer region and increase radial uniformity thereby was devised and herein is proposed. Dark matter (DM), graphite, stainless steel (SS) and borated stainless steel (BSS) were considered as shielding materials in a Monte Carlo-simulation-based evaluation of the radial uniformity of a Silicon Carbide (SiC) ingot. In the case of DM, the relative reaction rate at the center region of the ingot was increased; graphite did not enhance the radial uniformity; for both SS and BSS, the radial uniformity was under 1% with the optimized slot size. Therefore, it is expected that if the NTD technique is used in concert with the proposed slit method, semiconductors of exceedingly uniform dopant distribution can be produced.