Dislocation Control in High-Purity Germanium: Mapping Variations and Growth Knobs for Next-Generation HPGe Detectors

High-purity germanium (HPGe) underpins rare-event searches in neutrino and dark-matter physics, where charge transport uniformity and ultra-low noise are essential. We report a targeted study of radial and axial dislocation-density variations in a 4 kg Czochralski-grown crystal (Ø 8 cm, L = 15 cm) and identify growth-process "knobs" that govern these variations and, by extension, detector performance. Using controlled Dash necking and deliberate thermal-shock protocols, we varied neck diameters and introduced hold times with the seed positioned 1 cm above the melt (3, 5, 8, 12, 15 min) prior to dipping. The resulting maps reveal that dislocation generation and propagation concentrate near the seed–shoulder transition and evolve along the axis with sensitivity to both neck geometry and pre-dip thermal history. These observations establish a causal link between thermal-mechanical boundary conditions during shoulder formation and the eventual dislocation landscape, providing a practical pathway to tune crystal quality for low-leakage, high-collection-efficiency HPGe detectors. We discuss implications for wafer selection, device yield, and field uniformity in ring-contact and planar architectures, and outline a process window that prioritizes reproducibility for rare-event instrumentation.