Abstract
Neutron detection is a valuable tool in nuclear science research, homeland security, quality assurance in nuclear plants and other medical applications. There has recently been increasing interests in developing new approaches for neutron detectors in order to improve spatial resolution, detection efficiency and better integration with readout electronics. Semiconductor detectors can provide spatial resolution on a micrometre scale and are fully compatible with readout electronics. Neutrons are, however, non-ionising and cannot be detected directly by most semiconductor materials. A neutron converter material is therefore required to convert the incoming neutron particles into secondary particles that are detectable by semiconductor detectors and is deposited on the semiconductor detector's surface. Neutron detection efficiency is often rather low with such compositions due to the trapping of secondary particles in the neutron material layer and not reaching the detector's sensitive volume. By increasing the surface area of the window side of the detector, the total volume of convertor can be increased while keeping the thickness of the converter low. The neutron conversion efficiency should consequently improve due to an increased number of neutron captures and still allowing a good probability for the secondary particles to reach the sensitive volume. In this work, the surface area is increased by etching the window side of the silicon sensors using tetramethylammonium hydroxide (TMAH). The wet etchant etches along the <111> orientation of the silicon crystal plane and 3-dimensional pyramidal shapes are formed on the wafer surface (Fig.1). Silicon P-I-N diodes with such pyramids have been successfully fabricated. In addition, TiB2 a converter material that is compatible with silicon processing was successfully deposited on these pyramidal structures using Physical Vapour Deposition (PVD), and has previously been demonstrated on planar devices[1]. Electrical measurements on these sensor and the detectors' performances were studied using alpha particles and thermal neutrons.
