Cell formation in stanogermanides using pulsed laser thermal anneal on Ge0.91Sn0.09

Pulsed laser thermal annealing (LTA) has been thoroughly investigated for the formation of low-resistance stanogermanide contacts on Ge0.91Sn0.09 substrates. Three different metals (Ni, Pt, and Ti) were characterized using a wide laser energy density range (100–500 mJ/cm2). Electrical performance, surface quality, cross-sectional crystallographic, and elemental analysis have been systematically examined in order to identify the ideal process window. Electrical characterization showed that the samples processed by LTA had lower resistance variability compared with the rapid thermal anneal (RTA) counterpart. Among the three metals used, Ni and Pt were the most promising candidates for future sub-nm applications based on the low resistance values. The stanogermanide alloys suffered a high degeneration as the LTA thermal budget increased. Cross-sectional elemental analysis showed a highly unusual Sn segregation effect, particularly for high LTA energy densities, where vertical columns of Sn-rich alloy were formed, also known as cell formation, similar to that seen for Sb hyperdoping of Si when using LTA. This effect is linked to solid solubility and distribution coefficient of Sn in Ge, as well as the velocity of the liquid-solid interface during crystallization as the samples cool.