Improving metal/semiconductor conductivity using AlOx interlayers on n-type and p-type Si

Thermal atomic layer deposition was used to form ultra-thin interlayers in metal/interlayer/ semiconductor Ohmic contacts on n-type and p-type Si. AlOx of thickness 1–2 nm was deposited at 120 °C on Si substrates prior to metallization, forming Ni/AlOx/Si contacts. Conductivity improved by two orders of magnitude but the contacts remained rectifying. When they were annealed at 200 °C, the conductivity increased by another order of magnitude and the samples became Ohmic. A minimum specific contact resistivity of 1.5 × 10−4 Ω-cm2 was obtained for structures based on lightly doped (1015 cm−3) Si substrates. Existing models that describe Fermi level de-pinning do not fully explain our results, which are however consistent with other experimental data in the literature.