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

Abstract

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 anneal temperatures as low as 100 • 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 • C to 400-430 • 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 • C. Lowest contact resistance (0.05 ± 0.01 mm) is obtained when Ni thickness is about 25 nm for 100 nm AuGe layer thickness, anneal temperature is 400 • 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 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 proportional 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.

Superconductivity in AuNiGe Ohmic contacts to a GaAs-based high mobility two-dimensional electron gas

“…Many factors influence the contact resistance to a 2DEG: the depth of the 2DEG; the thickness of the AlGaAs layer; the sequence, thickness and composition of the contact metal layers; the target temperature of the rapid thermal annealer; the annealing time; the mobility of the 2DEG; and the quality of the sample surface before deposition. Low normalized contact resistances r c ∼ 0.05 Ωmm have been demonstrated 8 in 2DEGs with mobilities of ∼ 10 5 cm 2 /Vs; using similar recipes we have obtained r c ∼ 1 Ωmm in higher mobility 2DEGs.…”

Adhesion Characteristics of Pd∕Ge Ohmic Contacts on GaAs∕AlGaAs Multilayer Structures

“…The surface roughness is 10 times lower than that of AuGe/Ni/Au based contact which gives the lowest contact resistance [5]. The measured surface roughness is 2.0 0.5nm.…”

“…The optimum contact resistance of ∼ 0.75 0.1 -mm (table 2) is obtained which is about 15 times larger than that of structures with AuGe/Ni/Au that gave the lowest contact resistance [5].…”

Dependence of melting, roughness and contact resistances on Ge and Ni content in alloyed AuGe/Ni/Au-type electrical contacts to GaAs/AlGaAs multilayer structures

“…The recipe gives low contact resistances in the region of 0.03-0.1 mm; however, this is achieved at the expense of an increased surface roughness [7], a factor that influences the transistor gate fabrication. The surface roughness can be reduced by increasing the Nilayer thickness or decreasing the Ge content below that of the eutectic composition (88:12 wt%), albeit at the expense of increasing the contact resistance [8][9][10][11][12].…”

“…Residual magnetism, if any, of the processed metallization structure, is relevant to the magnetic field sensor application. 0268-1242/10/035002+05$30.00 Our efforts to track the contact resistance and magnetism of the structures, while optimizing process parameters such as anneal temperatures and Ni-layer thicknesses, revealed that the solid phase dissolution of Ni into AuGe takes place at temperatures much lower than that at which alloying takes place [12]. In this paper we report the results of magnetization, contact resistance and roughness studies and also of melting in the metallization structure, as the Ge content and Ni-layer thickness are varied.…”