Epitaxial Bi/GaAs diodes via electrodeposition

Epitaxial Bi/GaAs diodes have been formed by electrodeposition from bismuth nitrate and ammonium sulfate ((NH4)(2)SO4) aqueous solutions. Bi grows (0001) oriented on both GaAs (111)B and (001) substrates while it tilts 16 degrees to a (0 118) surface orientation for (011) GaAs. The metal orients in all cases with its {1120} planes parallel the GaAs {110} planes. Diodes prepared on (001), (111)B, and (011) wafers have current-voltage barrier heights Phi(IV)(B) that vary from 0.74, to 0.76, to 0.83 eV (n = 1.01-1.11), 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 Phi(IV)(B) results, 0.06-1.5 eV, as a function of the GaAs orientation, increasing in value in order of (011), (001), to (111)B. 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 (0001) 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. (c) 2006 American Vacuum Society.