Improvement of yield ratio of ohmic contact to GaAs/AlGaAs heterostructure by application of SiO2 protective layer

All the contact pads of a quantized Hall resistance (QHR) device should have a low contact resistance (∼1 Ω) for the application of DC resistance standard devices at cryogenic temperatures. Corrosion of a GaAs/AlGaAs substrate occurs along the edge of the photoresist before the deposition of Ni/AuGe, and we assume that this corrosion degrades the contact resistance. A SiO2 protective layer is effective in preventing the corrosion of and protecting the surface of GaAs/AlGaAs substrate. With the use of this SiO2 protective layer, the yield ratio of the contact resistance to the twodimensional electron gas (2DEG) layer at low temperature (∼0.5 K) and high magnetic field (∼9 T) improves to nearly 100%. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)