Dopant behavior in heavily doped polycrystalline Ge_1-xSn_x layers prepared with pulsed laser annealing in water

A low-temperature process for the formation of heavily doped polycrystalline Ge (poly-Ge) layers on insulators is required to realize next-generation electronic devices. In this study, we have systematically investigated pulsed laser annealing (PLA) in flowing water for heavily doped amorphous Ge_1-xSn_x layers (x ≈ 0.02) with various dopants such as B, Al, Ga, In, P, As, and Sb on SiO₂. It is found that the dopant density after PLA with a high laser energy is reduced when the oxidized dopant has a lower oxygen chemical potential than H₂O. As a result, for the p-type doping of B, Al, Ga, and In, we obtained a high Hall hole density of 5 × 10¹⁹ cm^-3 for PLA with a low energy. Consequently, the Hall hole mobility is limited to as low as 10cm²V^-1 s^-1. In contrast, for As and Sb doping, because the density of substitutional dopants does not decrease even after PLA with a high energy, we achieved a high Hall electron density of 6 × 10¹⁹ cm^-3 and a high Hall electron mobility simultaneously. These results indicate that preventing the oxidation of dopant atoms by water is an important factor for achieving heavy doping using PLA in water.