Abstract
<title>Abstract</title> <p>Cadmium zinc telluride (CZT) is an ideal material for photon-counting detectors. In CZT crystal growth, the seed fusion interface can be designed with a shoulder structure, enabling large-diameter crystals to be grown from small, non-isodiametric seeds while significantly reducing seed procurement costs. In this study, three shoulder angles of 0°, 90°, and 120° were designed for seeded THM crystal growth experiments. The seed fusion zones of the resulting ingots were characterized in terms of morphology, stress distribution, and Te inclusion behavior. The results demonstrate that non-isodiametric seeds of a suitable diameter show potential for grain enlargement. However, the shoulder geometry is associated with intensified thermoelastic stress at the ingot edge, which tends to propagate inward. Within this stress field, Te inclusions show increased size and density, and these changes correspond to reduced detector electrical performance. In addition, a distinct boundary between the central main grain and the parasitic edge grains is observed at the fusion interface in ingots grown from non-isodiametric seeds. Within the parasitic edge grains zone, large Te inclusions exceeding 50 µm in size, along with micron-scale voids are identified. Among the three configurations, the planar detector fabricated from the crystal grown with isodiametric seed (0° shoulder) delivers the best performance, with a resistivity of 1.62 × 10¹⁰ Ω·cm and an energy resolution of 4.95% under ²⁴¹Am (59.5 keV) irradiation.</p>