Hyperdope and highly strained Ge:Sb layersby Pulsed Laser Melting for Next-generation Germanium Crystalline Gamma-Ray sources

The requirement of induced highly controlled deformation in germanium has become prominent in various research areas, including nanoelectronics, photonics, photovoltaics, and gamma ray production [1,2,3]. Pulsed laser melting (PLM) techniques have recently been shown to be a successful strategy for achieving such highly strained states. This effectiveness is primarily due to the ability to introduce a high concentration of impurity atoms within the first few hundred nanometres of silicon and germanium. Remarkably, successful experiments have been conducted with antimony and tin atoms, demonstrating incorporation levels significantly exceeding their equilibrium solid solubilities [3,4]. The resulting layer exhibits excellent crystalline quality, attributed to the epitaxial regrowth that occurs during the extremely fast post-laser material cooling. Moreover, by exploring various laser parameters, it is possible to produce either pseudomorphic or relaxed surface layers, each serving different technological purposes [1]. In this study, different germanium crystal orientations <001>, <110>, and <111> were investigated to determine the maximum incorporation limits. The results highlight the remarkable versatility and strong potential of this technique in the advancement of strain engineering in germanium. Various applications of strain engineering using pulsed laser melting (PLM) will be discussed, with a primary focus on the fabrication of germanium crystalline undulators. Through the heavy antimony doping of germanium, the first crystalline undulators produced by this technique have been fabricated and characterised. Their key properties will be reviewed, demonstrating significant promise for gamma-ray generation. [1] F. Sgarbossa et al. Applied Surface Science 2026, 730, 166200 [2] S. Bertoldo et. al. Material Science in Semiconductor Processing 2025, 200, 109967 [3] C. Carraro et al. Applied Surface Science 2020, 509, 145229 [4] E. Di Russo et al. Applied Surface Science 2023, 612, 155817