Epitaxial Fe[sub x]Ni[sub 1−x] Thin Film Contacts to GaAs via Electrochemistry

Abstract

The galvanostatic electrodeposition of epitaxial Fe x Ni 1−x films on n-GaAs͑001͒ substrates from aqueous metal ammonium sulfate solutions is reported. Structural measurements using X-ray diffraction and transmission electron microscopy indicate that the films have single crystalline or highly oriented body-centered cubic ͑bcc͒ or face-centered cubic ͑fcc͒ structure at Fe and Ni-rich compositions, respectively. The preparation of the substrate surface via ammonium hydroxide as well as the usage of an ammonium sulfate electrolyte buffer facilitates the initial nucleation of aligned metal islands on GaAs. The ratio of the Fe atomic concentration in the fcc films to that in the electrolyte is close to unity ͑1.1͒, whereas a preferential incorporation occurs for the bcc phase such that this ratio increases linearly with Fe atomic composition at a rate of 3.7. bcc Fe x Ni ͑1−x͒ /GaAs diodes have uniform Schottky barrier heights as measured by current-voltage measurements independent of Fe composition consistent with a high interfacial state density. The observed magnetic properties of Fe x Ni 1−x are consistent with single crystalline material with distributed inhomogeneities. The epitaxy via electrodeposition suggests the importance of ammonium sulfate for technical applications.

Role of Hydrogen Evolution during Epitaxial Electrodeposition of Fe on GaAs

“…Electrodeposition of epitaxial Fe films on GaAs has been proposed as an efficient alternative to physical deposition methods. [8][9][10][11][12][13][14] The low-energy character of the electrodeposition technique means that interface intermixing 15 is largely avoided. In general, Fe deposition on GaAs proceeds via island nucleation, coalescence, and subsequent film growth, which for electrodeposition is typically at rates of 2-6 nm/s, perhaps 100 times faster than MBE.…”

Lateral spin injection and detection through electrodeposited Fe/GaAs contacts

“…[23,24] The tensile strain is consistent with a bulk oxygen concentration (< 1 at%) that results in a reduction in the electrodeposited Fe lattice constant by 0.2% and correlates with heterogeneous magnetic properties. [24,25] Electrical measurements (current versus voltage) were carried out using a computercontrolled probe station. Magnetization hysteresis curves of blanket films were measured using a SQUID magnetometer with a reciprocating sample option (RSO) where the sample is placed at the center of the SQUID pick-up coil and oscillated by a servo motor during measurements.…”

“…Theelectrodepositionwas carried out galvanostatically (15 mA/cm 2 ) at room temperature in an aqueous solution of ferrous sulphate (0.1 M) buffered with ammonium sulphate (0.3 M)(pH 4). [23,24] The GaAs substrate was the cathode with a Pt rod used as a counter electrode. Prior to deposition, the GaAs was etched in ammonium hydroxide solution (10 % in de-ionized water, 12 sec) and rinsed in de-ionized water.…”

Electrodeposition of Iron and Iron Alloys

“…Iron and iron-nickel alloy deposits have attracted increasing attention as components in spintronics with a semiconductor such as gallium-arsenide (GaAs), where the quality, including preferred orientation and lattice mismatch to the semiconductor is important. [178,179] …”