Single-crystalline, body-centered-cubic Fe films have been electrodeposited on n-GaAs (001)-, (111)-, and (110)-oriented substrates from ferrous ammonium sulphate [Fe(NH4)2SO4] electrolytes. The purity of the epitaxial Fe films (lattice constant), and the quality of the epitaxy as indicated by x-ray diffraction and transmission electron microscopy, is comparable to vacuum-deposited films. The films nucleate as islands that strain relax before coalescing into continuous layers. The resulting interfaces are atomically abrupt and the films are magnetic with easy magnetization axes the same as that for bulk iron.

Epitaxial Bi/ GaAs diodes have been formed by electrodeposition from bismuth nitrate and ammonium sulfate ͑͑NH 4 ͒ 2 SO 4 ͒ aqueous solutions. Bi grows ͑0001͒ oriented on both GaAs ͑111͒B and ͑001͒ substrates while it tilts 16°to a ͑011 គ 8͒ surface orientation for ͑011͒ GaAs. The metal orients in all cases with its ͕112 គ 0͖ planes parallel the GaAs ͕110͖ planes. Diodes prepared on ͑001͒, ͑111͒B, and ͑011͒ wafers have current-voltage barrier heights ⌽ B IV that vary from 0.74, to 0.76, to 0.83 eV ͑n = 1.01-1.11͒, respectively. These barrier heights straggle values from earlier reports for polycrystalline Bi deposited by ultrahigh vacuum techniques or electrodeposition. Barrier heights measured from high frequency, capacitance-voltage characteristics are higher than the ⌽ B IV results, 0.06-1.5 eV, as a function of the GaAs orientation, increasing in value in order of ͑011͒, ͑001͒, to ͑111͒B. This is explained by a combination of image force lowering and field emission corrections, and interface state/dipoles that are likely dependent on the GaAs orientation and on the degree of ͑0001͒ Bi alignment. These results are supported by cross-sectional transmission electron microscopy investigations indicating abrupt Bi/ GaAs interfaces without evidence of a significant interfacial oxide or reacted layer.

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.

Bismuth films formed by electrodeposition on n-GaAs (111) at 70°C are found to be single crystalline, (0001) oriented, with trigonal surface morphologies typical of high quality single crystals. Diode current-voltage characteristics display low reverse-bias leakage currents and average barrier heights of 0.77±0.02eV (n=1.07). A necessary requirement for single crystalline growth is the presence of ammonium sulfate in the electrolyte.

The residual stress in Cu films epitaxially grown on GaAs͑001͒ single crystalline substrates has been compared to polycrystalline Cu growth on ͑111͒ textured Au substrates, both grown via the same galvanostatic electrodeposition process. Optimized Cu/GaAs epitaxial nucleation and growth was obtained with a substrate pre-etch in dilute ammonium-hydroxide followed by electrodeposition in a pure Cu sulfate aqueous electrolyte at elevated temperatures. The resulting films are single crystalline, and strain relaxed, as measured by X-ray and electron diffraction. The ͑001͒ surfaces developed square pyramidal facets that increase in average size with increasing current density. In situ wafer curvature measurements found that the Cu/GaAs films followed the commonly observed change from compressive to tensile and finally to compressive stress ͑−200 MPa͒ that quickly relaxed once growth was interrupted. In contrast, polycrystalline Cu/Au films developed a smaller and constant tensile stress ͑+10 MPa͒ that relaxed more slowly. Given the similar growth rates of the two systems, differences in residual stress are related to differences in the density and nature of the coalescence boundaries and associated surface adatom processes. The resulting electrical properties of Cu/GaAs diodes show an interfacial capacitance that is consistent with interdiffusion and the reaction layer detected by electron microscopy.