Stoichiometric Effects on the Photoelectric Properties of LiInSe₂ Crystals for Neutron Detection

Abstract

6LiInSe2 is a promising semiconductor candidate for thermal neutron detection due to its large capture cross-section. However, the charge collection efficiency is still insufficient for high resolution for the grown-in defects induced by the stoichiometric deviation. In this work, we report photoelectric properties of stoichiometric LiInSe2 crystal boules up to 70 mm in length and 20 mm in diameter grown by the vertical Bridgman method. Inductively coupled plasma measurements demonstrate that the ratio of Li, In, and Se of the as-grown crystal is very close to 1:1:2, which is optimized by low temperature synthesis processing. The obtained single crystals display high bulk resistivity in the range of 1011–1012 Ω·cm and a direct band gap of 2.01–2.83 eV with a changeable color from red to yellow. The electronic structure of LiInSe2 was studied using first-principles density functional theory calculations, which predicts that the antisite defects of InLi and LiIn are the dominant factor for the different crystal colors observed. The stoichiometric LiInSe2 crystal gives an improved energy resolution, for a semiconductor detector when illuminated with a 241Am@5.48 MeV α source, of 23.3%. The electron mobility-lifetime product (μτ) is ∼2.5 × 10–5 cm2 V–1.

Non-stoichiometry and point native defects in non-oxide non-linear optical large single crystals: advantages and problems

“…In search of effective indicators of defects, many works were performed. 3,63–68 In LISe crystals grown by the B technique, antisite defects of In Li and Li In were identified experimentally via color, actual composition and band gap in combination with theoretical calculation. 63 Herein, even with seemingly optimal technology, red as-grown crystals were defective and converted to yellow on annealing in the presence of LISe polycrystalline material.…”

“…3,63–68 In LISe crystals grown by the B technique, antisite defects of In Li and Li In were identified experimentally via color, actual composition and band gap in combination with theoretical calculation. 63 Herein, even with seemingly optimal technology, red as-grown crystals were defective and converted to yellow on annealing in the presence of LISe polycrystalline material. With composition of LiIn 1.06 Se 2 , E g = 2.86 eV and overall transparency >70%, such crystals were identified as almost free from grown-in defects.…”

“…In several works, non-stoichiometry was determined by direct methods using ICP OES or ICP AES techniques. 63,68 In ref. 68, in spite of a quite moderate accuracy (3 rel%) of the chemical analyses, the defect models deduced from the chemical data coincided appropriately with the models deduced from optical, electrical and spectroscopic measurements.…”

LiInSe2 for Semiconductor Neutron Detectors

“…6 LiInSe 2 crystals were grown by the Vertical Bridgman (VB) technique, following methods described in the literature [2,[5][6][7]. Semiconductor grade high-purity indium and selenium were FIGURE 1 | 6 LiInSe 2 ingot (G77) after crystal growth.…”

“…LiInSe 2 has a wide bandgap and high resistivity, allowing for detectors for room-temperature operation with low noise (low leakage current) [2]. Several crystals of LiInSe 2 with varying conditions were grown and characterized.…”