Electronic and morphological structures of semiconductor electrodes

After a brief description of the electronic structure at semiconductor-electrolyte interface is given, in situ determinations of electronic and morphological structures as semiconductor electrodes by electrochemical tunneling spectroscopy (ETS) and atomic force microscopy (AFM), respectively, are described. In situ ETS is applied to p-and n-GaAs electrodes in HCIO₄ solution and results at n-GaAs electrode are analyzed semiquantitatively. In situ electrochemical AFM shows that an atomically ordered structure of p-InSe surface is lost when positive potential is applied as result of anodic decomposition (InSe+H₂O→ Se+InOH²+ +H⁺+3e⁻). An atomically ordered structure is, however, recovered if negative potential is applied because the deposited Se is removed reductively at negative potentials (Se+ H⁺+2e⁻→HSe⁻). In situ electrochemical AFM is also applied to investigate the surface structure of p-GaAs. The atomically ordered GaAs (100)-(1×1) structure is observed in electrolyte solutions in contrast to the results in vacuum where the surface is reconstructed, showing the important roles of ions. Electrochemical deposition of Cu on p-GaAs(100) surface is strongly affected by surface defects, applied potential, and the concentration of Cu²⁺ ion in solution. Atomically resolved Cu(111)-(1×1) structure is observed on top of the Cu deposits, but GaAs (100) - (1×1) structure is still observed other portions of the surface, suggesting the weak interaction between the substrate (GaAs) and Cu.