Nanoscale n⁺⁺-p junction formation in GeOI probed by tip-enhanced Raman spectroscopy and conductive atomic force microscopy Available to Purchase

Ge-on-Si and Ge-on-insulator (GeOI) are the most promising materials for the next-generation nanoelectronics that can be fully integrated with silicon technology. To this day, the fabrication of Ge-based transistors with a n-type channel doping above 5 × 10¹⁹ cm⁻³ remains challenging. Here, we report on n-type doping of Ge beyond the equilibrium solubility limit (n_e ≈ 6 × 10²⁰ cm⁻³) together with a nanoscale technique to inspect the dopant distribution in n⁺⁺-p junctions in GeOI. The n⁺⁺ layer in Ge is realized by P⁺ ion implantation followed by millisecond-flashlamp annealing. The electron concentration is found to be three times higher than the equilibrium solid solubility limit of P in Ge determined at 800 °C. The millisecond-flashlamp annealing process is used for the electrical activation of the implanted P dopant and to fully suppress its diffusion. The study of the P activation and distribution in implanted GeOI relies on the combination of Raman spectroscopy, conductive atomic force microscopy, and secondary ion mass spectrometry. The linear dependence between the Fano asymmetry parameter q and the active carrier concentration makes Raman spectroscopy a powerful tool to study the electrical properties of semiconductors. We also demonstrate the high electrical activation efficiency together with the formation of ohmic contacts through Ni germanidation via a single-step flashlamp annealing process.