Static sublimation purification process and characterization of LiZnAs semiconductor material

Abstract

Refinement of the class A I B II C V materials continue as a candidate for solid-state neutron detectors. Such a device would have greater efficiency, in a compact form, than present day gasfilled 3 He and 10 BF 3 detectors. The 6 Li(n,t) 4 He reaction yields a total Q value of 4.78 MeV, larger than 10 B, and easily identified above background radiations. Hence, devices composed of either natural Li (nominally 7.5% 6 Li) or enriched 6 Li (usually 95% 6 Li) may provide a semiconductor material for compact high efficiency neutron detectors. A sub-branch of the III-V semiconductors, the filled tetrahedral compounds, A I B II C V , known as Nowotny-Juza compounds, are known for their desirable cubic crystal structure. Starting material was synthesized by equimolar portions of Li, Zn, and As sealed under vacuum (10-6 Torr) in quartz ampoules with a boron nitride lining, and reacted in a compounding furnace [1]. The synthesized material showed signs of high impurity levels from material and electrical property characterization. In the present work, a static vacuum sublimation of synthesized LiZnAs loaded in a quartz vessel was performed to help purify the synthesized material. The chemical composition of the sublimed material and remains material was confirmed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Lithium was not detected in the sublimed material, however, near stoichiometric amounts of each constituent element were found in the remains material for LiZnAs. X-ray diffraction phase identification scans of the remains material and sublimed material were compared, and further indicated the impurity materials were removed from the synthesized materials. The remaining powder post the sublimation process showed characteristics of a higher purity ternary compound.

Device fabrication, characterization, and thermal neutron detection response of LiZnP and LiZnAs semiconductor devices

“…The synthesized material was purified by a static sublimation process. The process appeared to successfully separate both the ternary LiZnP and LiZnAs material, from elemental and binary residual materials that often result from the synthesis process [2,3]. This purified LiZnP and LiZnAs material were subsequently grown into bulk crystals under a high-temperature vertical Bridgman technique [4,5].…”

“…Material purification post ternary synthesis [2,3] reduced the conductivity, and employing Ti/Au contacts also helped produce relatively stable devices, where silver epoxy contacts always resulted in high conductivity devices. Many devices fabricated from bulk grown ingots processed from the in-house synthesized and purified material exhibited a typical ohmic resistance I-V curve, as shown in Fig.…”

“…Laser pulses of 337 nm photons were traced with LiZnAs samples. The LiZnAs sample of dimensions 1.59 x 1.39 x 1.42 mm 3 was placed between the contacts of a project box. A 10.0 volt bias was applied to the sample (at the device) and the laser was set to pulse at approximately 1 Hz.…”

“…LiZnP was studied in the past as a possible radiation detector material [22], however there is no evidence of a published document from that particular study. In this study, the ternary products, LiZnP and LiZnAs were synthesized, purified and grown into bulk crystalline ingots [1][2][3][4][5]. Described in the following study is a procedure for device fabrication from LiZnP and LiZnAs materials, and details of the subsequent device characterization.…”

Anomalous sublimation passivation of nanotwinned silver particles

“…Sublimation is a first-order phase transition in which atoms break away from their neighbors in the crystal lattice and are transformed into the gas phase. Understanding sublimation mechanisms could impose great influences not only on scientific advances but also on a variety of technological applications including purification [1], sublimation deposition [2] and machining MEMS devices [3]. Due to its high chemical stability and low sublimation temperature, silver (Ag) nanocrystal with a face-centered cubic structure has been deemed as an ideal model material to exploit metal sublimation procedures.…”