Influence of Nickel layer thickness on the magnetic properties and contact resistance of AuGe/Ni/Au Ohmic contacts to GaAs/AlGaAs heterostructures

• Published in: Journal of physics. D, Applied physics Applied physics, 2009-06, Vol.42 (12), p.125104-125104p8
• Main Authors: Abhilash, T S, Ravi Kumar, Ch, Rajaram, G
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Contact resistance, contact potential; Domain effects, magnetization curves, and hysteresis; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in interface structures; Exact sciences and technology; Interfacial magnetic properties (multilayers, magnetic quantum wells, superlattices, magnetic heterostructures); Magnetic properties and materials; Magnetic properties of surface, thin films and multilayers; Magnetization curves, magnetization reversal, hysteresis, barkhausen and related effects; Physics
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/42/12/125104

The magnetization of alloyed Ohmic contact film structures of the form AuGe/Ni/Au deposited on a GaAs/AlGaAs heterostructure substrate are reported as functions of Ni-layer thickness and alloying temperature. The observations are correlated with contact resistance and surface morphology studies. It is found that drops in magnetization, due to conversion of Ni to a non-magnetic phase or alloy, begin at annea1 temperatures as low as 100 deg C for all Ni-layer thicknesses. The conversion is completed at an anneal temperature, T(a), that increases with Ni-layer thickness. T(A) varies from 100-200 deg C to 400-430 deg C as Ni-layer thickness is varied from 10 to 100 nm for an AuGe (88:12 wt%) layer thickness of 100 nm. The electrical contact formation, however, appears to begin at much higher temperatures than 100 deg C. Lowest contact resistance (0.05 0.01 Omega mm) is obtained when Ni thickness is about 25 nm for 100 nm AuGe layer thickness, anneal temperature is 400 deg C and anneal duration is 60 s. This contact is non-magnetic. Measurements on samples with other AuGe layer thicknesses suggest that the contact resistances are comparable to this (optimum value, if the ratio of AuGe layer thickness to that of Ni is greater-than or equal to 4. Increasing the Ni-layer thickness reduces the roughness of annealed contacts, but also increases contact resistance. The magnetic measurements are suggestive of a transformed Ni-layer thickness proprtional to the thickness of the underlying AuGe layer. It is proposed that Ni diffuses into AuGe in a concentration limited diffusive mechanism followed by segregation into Ni(3)Ge.