High defect density regions in neutron irradiated high-purity germanium: Characteristics and formation mechanisms

Abstract

A tentative model which reveals the existence of p-type regions with a significant spatial extension in either p- or n-type fast neutron irradiated high-purity germanium is presented. This model is based on transient capacitance spectroscopy data. The regions described here are present after room-temperature neutron irradiation in a material with a preirradiation free-carrier concentration at 77 K of around 1011 cm−3. They are characterized by the presence of a high concentration of point defects. Previous measurements show that these point defects act as shallow and deep acceptors. Simple calculation allows the estimation of the shallow acceptor concentration inside these regions from experimental data as well as the average size of such high defect density regions. The microscopic origin of the point defects located in these regions is also discussed. The data gives some basic insight into the properties of defects induced by displacement cascades in elemental semiconductors. Despite some limitations in the quantitative approach, this study also provides new elements for the understanding of neutron induced defects in lightly doped germanium.