Recrystallization of Ion Implantation Damage in GeSn Thin Films by Thermal and Laser Annealing

GeSn alloys are emerging as promising materials for infrared photonics due to their tunable direct bandgap and compatibility with silicon technology. Compared to in situ doping with limitations in doping area and possible Sn loss [1], ex situ doping via ion implantation offers greater customizability and potential for advanced device structures. Being the most commonly used doping method for high doping level, ion implantation faces challenges in repairing the damaged layers post-implantation, which would otherwise degrade optical and electrical properties of the material. The annealing condition of GeSn amorphized by implantation is limited by the low solubility of Sn in Ge, leading to the possibility of Sn diffusion and segregation [2]. While rapid thermal annealing (RTA) is a valid method to recrystallize amorphized epilayers [3], a consolidated understanding of crystallinity recovery of implanted GeSn and Sn segregation mechanism therein remains lacking.<br/><br/>In this work, we investigate the recovery of crystallinity in epitaxially grown Ge_0.89Sn_0.11 implanted with arsenic at two doses of 2×10¹³ cm^-2 and 1×10¹⁴ cm^-2 at 40 kV, corresponding to peak doping concentrations of 5×10¹⁸ cm^-3and 2.5×10¹⁹ cm^-3, using RTA and laser annealing. We propose a model of Sn diffusion pathways in segregation events based on strain relaxation through misfit and threading dislocation formation, consistent with distinct Sn segregation patterns in GeSn layers with varying degrees of ion-induced amorphization. Our results show the critical role of temperature in the repair of ion-damaged GeSn crystal. RTA at 400 °C effectively restores crystallinity in Ge_0.89Sn_0.11 films. Photoluminescence (PL), electron backscatter diffraction (EBSD) and Raman spectroscopy analyses reveal the evolution of crystallinity of Ge_0.89Sn_0.11 epilayers subjected to implantation and subsequent annealing and verifies the effective lattice restoration. These characterizations, combined with ion implantation modeling, suggest that a full damage recovery can be achieved by RTA for implantation peak concentration &lt; 1×10¹⁹ cm^-3. At a higher implantation dose corresponding to 2.5×10¹⁹ cm^-3peak doping concentration, most of the layer can be recovered except for some of the very top region within ~20 nm of the surface that suffers heavier implantation damage. To this end, continuous wave laser annealing at a 532 nm wavelength and a power density of ~200 kW/cm² achieves better recrystallization without Sn segregation compared to RTA results with sporadic surface segregation. This highlights the improved effectiveness of laser annealing in lattice recrystallization particularly for high-dose implantation, where traditional RTA may fall short. These findings not only extend previous knowledge of implantation damage in GeSn epilayers [4] and offer insights into macroscale Sn segregation mechanisms, but also provide guidelines for optimizing the annealing conditions for GeSn post-implantation. The study further supports the integration of GeSn in silicon photonics and paves the way for more sophisticated doping profiles and enhanced device functionalities.<br/><br/>Reference<br/>[1] Tsai, C.-E.; Lu, F.-L.; Chen, P.-S.; Liu, C. W. Boron-Doping Induced Sn Loss in GeSn Alloys Grown by Chemical Vapor Deposition. <i>Thin Solid Films</i> <b>2018</b>, <i>660</i>, 263–266.<br/>[2] von den Driesch, N. <i>et al.</i> Thermally Activated Diffusion and Lattice Relaxation in (Si)GeSn Materials. <i>Phys. Rev. Mater.</i> <b>2020</b>, <i>4</i>, 033604.<br/>[3] Chen, R. <i>et al.</i> Material Characterization of High Sn-Content, Compressively-Strained GeSn Epitaxial Films after Rapid Thermal Processing. <i>J. Cryst. Growth</i> <b>2013</b>, <i>365</i>, 29–34.<br/>[4] Amoah, S. <i>et al.</i> Effects of Ion Implantation with Arsenic and Boron in Germanium-Tin Layers. <i>J. Vac. Sci. Technol. B</i> <b>2024</b>, <i>42</i>, 34002.