Investigation of the diffusion and crystal growth of CdZnTe in Te solution using the traveling heater method under axial static magnetic field†

Abstract

Nowadays, CdZnTe nuclear detectors are a research hotspot in fields of photon-counting nuclear medical imaging and environmental monitoring. The traveling heater method (THM) has been demonstrated to be a promising way to grow high-quality detector-grade CdZnTe crystals. However, low growth velocity (3–5 mm per day) during the THM growth of CdZnTe hinders its commercial applications. In this work, six sets of solute diffusion experiments and four groups of crystal growth experiments were conducted to investigate the influence of axial static magnetic field (SMF) on solute interdiffusion in Te solution and crystal growth during the THM growth of CdZnTe crystals. Under 5T SMF, solute interdiffusion velocity in CdZnTe polycrystals above pure Te solvents increased from 30.28 mm h⁻¹ to 32.54 mm h⁻¹, while in CdZnTe polycrystals below pure Te solvents, it increased from 0.28 mm h⁻¹ to 1.17 mm h⁻¹. The introduction of SMF induces thermoelectric magnetic convection (TEMC) near the solid–liquid interface, which enhances the interdiffusion of CdZnTe in Te solutions. During the THM growth of CdZnTe crystals, in the absence of SMF, the growth interface turned from slightly concave at a growth velocity of 0.3 mm h⁻¹ to a growth interfacial region at a growth velocity of 0.9 mm h⁻¹. Under 5T SMF, the growth interface turned from convex at 0.3 mm h⁻¹ to wave-like at 0.9 mm h⁻¹. The convex interface at 5T SMF facilitated single-crystalline growth, such that the crystalline yield increased from nearly 50% to 60% at 0.3 mm h⁻¹ and decreased the concentration of Te inclusions by one order of magnitude from 10⁵ cm⁻³ to 10⁴ cm⁻³. Meanwhile, the introduction of 5T SMF changed the crystal growth direction from [111] to [422]. As a result, adopting THM growth under 5T SMF and a growth velocity of 0.3 mm h⁻¹, CdZnTe crystals with high crystalline yield (60%), uniform distribution of Te inclusions (a size of 3–10 μm and a concentration of 1.21 × 10⁴ cm), and high energy resolution (6.8%) with an MSM detector structure (²⁴¹Am irradiation) were obtained.