Elemental Analysis and Current-Voltage Characteristics of LiZnP and LiZnAs Samples for Solid-State Neutron Detectors

Research for a reliable solid-form semiconductor neutron detector continues because such a device would have greater efficiency, in a compact form, than present day gas-filled He and BF3 detectors. The Li(n,t)He reaction yields a total Q value of 4.78 MeV, larger than B, and easily identified above background radiations. Hence, devices composed of either natural Li (nominally 7.5% Li) or enriched Li (usually 95% Li) may provide a semiconductor material for compact high efficiency neutron detectors. A sub-branch of the III-V semiconductors, the filled tetrahedral compounds, ABC, known as Nowotny-Juza compounds, are known for their desirable cubic crystal structure, and were originally studied for photonic applications. Equimolar portions of Li, Zn, and P or As were sealed under vacuum (10 Torr) in quartz ampoules with a graphite lining, loaded into a compounding furnace, and heated to 560 C to form the ternary compound, LiZnP or LiZnAs, and further annealed to promote crystallization. The chemical composition of the synthesized starting material was confirmed at Galbraith Laboratories, Inc. by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), which showed the compounds were reacted in equal ratios, 1-1-1, to form ternary compounds. Bulk single crystal samples were grown by a high temperature technique described elsewhere [1]. Samples were cut, polished, and prepared for electrical characterization by depositing a Ti/Au contact onto one side of the one of the samples and using silver epoxy to form the other contact. Current-voltage curves were collected for a sample with silver epoxy for both anode and cathode contact, and for a sample with a Ti-Au anode contact and silver epoxy cathode contact. A much higher resistivity was calculated, 6.6 x 10 Ω·cm, for the sample with a Ti-Au contact compared the high conductivity seen with the sample using silver epoxy contacts.