Lithium-free hyperpure germanium detectors with enhanced thickness, area, and segmentation via pulsed laser melting

In this work, we present the optimization process of an innovative technology to create a thin, thermally stable, and segmentable n-type junction for the fabrication of segmented hyperpure germanium (HPGe) detectors. The core of this approach involves depositing doping atoms through magnetron sputtering and diffusing them into germanium using the Pulsed Laser Melting (PLM) technique. PLM enables rapid melting of a thin germanium layer, allowing substitutional incorporation of dopants during the subsequent epitaxial regrowth. In previous works, we have successfully used this technology for producing junctions on small-sized detectors. Here, we extend the application of the technology to larger-area, segmented, and thick detectors. Initially, we developed a thin prototype detector featuring six segments, demonstrating the feasibility of the PLM junction. Spectroscopic measurements revealed good energy resolution and the capability for gamma-ray position identification. Crucially, the junction proved thermally stable after annealing typically used for neutron damage recovery. We then extended this technology to thicker detectors up to 2 cm, requiring optimization of each process step due to the junction thinness and abruptness. Improvements included dust reduction, chemical surface cleaning, gold-free photolithography, chemical-mechanical polishing, and contact pressure reduction using metal-coated polymer sheets. The optimized process yielded a detector prototype with breakdown voltage significantly higher than the depletion voltage, enabling its effective use as gamma radiation detector. This technology paves the way for next-generation segmented HPGe detectors with precise event localization, enhancing imaging and tracking capabilities for applications in nuclear physics, medical diagnostics, homeland security, and space research.