Fig. 3: Diffusion of nickel into b-As and the effects on FET performance.

a A set of BF-TEM images of the stack of Si/SiO₂ substate, b-As film, deposited polycrystalline Ni, and the interfacial Ni₁₁As₈ layer showing the expansion of the Ni₁₁As₈ layer with time at temperature T₁ = 267 °C. Scale bar is 30 nm. b, c The thickness of the Ni₁₁As₈ layer as a function of \(\sqrt{t}\) measured when the sample was kept at 267 ± 1 °C and 208 ± 2 °C showing a linear relationship. The slopes of the linear fits are 13.21 nm min^−1/2 at 267 °C and 1.77 nm min^−1/2 at 208 °C. The error bars are based on a statistical analysis of layer thicknesses. d Calculated thickness of the Ni₁₁As₈ layer as a function of time for different temperatures based on the estimated diffusion coefficient, \(D\left(T\right)\). e Schematic of the as-fabricated b-As channel FET with a global SiO₂/Si back gate. It also depicts the interfacial Ni₁₁As₈ layer and two different paths for charge transfer between Ni₁₁As₈ contact and b-As (red arrows). f Charge transfer characteristics: drain current vs gate voltage of 13 nm-thick b-As channel FETs at T_R and at two elevated temperatures: 100 and 150 °C. g SEM image with EDX elemental maps of Ni (yellow), b-As (green), and Au (purple) of a b-As channel FET after heating it to 150 °C showing diffusion of Ni into the b-As channel. EDX maps were constructed using As and Ni L, and Au M emissions. Scale bars are 1 μm.