Ex-situ incorporation of Al in Ge by sputter deposition and pulsed laser melting: a new approach to fabricate hyper-doped Ge:Al alloys

Abstract

Ge has garnered significant attention for its applications in nanoelectronics, mid-infrared photonics, gamma radiation detection and quantum devices. At present, a critical challenge is achieving dopant concentrations beyond the equilibrium solubility limit, a process known as hyper-doping, while preventing dopant segregation and deactivation. Pulsed laser melting (PLM) offers a nanosecond-scale, non-equilibrium solution that enables highly localized melting and epitaxial regrowth, significantly enhancing both crystallinity and dopant activation compared to conventional annealing and growth methods. This study introduces a novel ex-situ approach to synthesize hyper-doped Ge via sequential deposition of thin Al and Ge layers using magnetron sputtering, followed by PLM to drive Al diffusion and activation within the Ge matrix. This method suggests that a record hole concentration of 3 × 10²¹ cm⁻³ with 100 % electrical activation could be achieved. In addition, comprehensive electrical, structural, and chemical characterization provides new insights into the melting and recrystallization dynamics under various processing conditions, offering a deeper understanding of the phenomena leading to hyper-doping.