Electrical and magnetic properties of ohmic contacts of the quantum hall resistance devices

摘要

Quantum Hall effect is used to realize resistance standard which is in terms of the Planck constant h and elementary charge e in metrology. The quantum Hall resistance devices are fabricated based on two-dimensional electron gas formed in GaAs/AlxGa1-x as heterostructures. Low-resistance Ohmic contact to the 2DEG is crucial in fabricating quantum Hall devices to obtain reproducible and accurate results. Annealed Au/Ge/Ni multilayer is widely used for Ohmic contacts to GaAs. In this paper, electrical and magnetic properties of optimized Ohmic contacts of quantum Hall devices are studied. For the electrical property evaluation, contact resistances are measured by three-terminal method in the quantum Hall i = 2 plateau regime. Most of the contacts were Ohmic with values less than 2.4 Omega and a good yield of better than 99% is obtained. In the magnetic property study, the annealed Au/Ge/Ni multilayer shows much smaller magnetization than the as-deposited one. TEM-EDS study shows the pure Ni layer diffused into the GaAs and AlGaAs layer and converts into the compounds closed to Ni2GeAs and NiAs phase. Density functional theory is used to calculate the atomic moments of pure face-centered cubic Ni, hexagonal Ni2GeAs and NiAs. The calculation results explained the magnetization drop of annealed samples well.