Radiation measurements after irradiation of silicon for neutron transmutation doping

Neutron transmutation doping of semiconductors is an important method for applications that require high dopant homogeneity. For silicon, it is based on the conversion of 30Si into 31P through a 30Si (n,γ) 31Si reaction during neutron irradiation following beta decay of 31Si to 31P. Neutron irradiation is usually performed in research reactors. The main characteristics of a doped silicon sample are (1) purity of the original silicon, (2) average phosphorus concentration and (3) phosphorus concentration homogeneity (uniformity). This paper describes measurement methods that utilise radiation induced during doping irradiation to measure these characteristics. The first two parameters can be measured using gamma spectrometry. The main part of the paper deals with homogeneity measurement. It describes a measurement method that is based on the detection of beta radiation from 31Si. Examples of experimental results are given. The experiments were performed in the LVR-15 research reactor. ► Silicon characteristics can be measured by radiation detection after neutron transmutation doping. ► Purity of the original silicon can be measured by neutron activation analysis. ► Average phosphorus concentration can be measured using gamma spectrometry. ► Phosphorus concentration homogeneity can be measured by detection of beta radiation from 31Si.