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Schottky contacts to n-GaAs have been fabricated by means of a photoelectrochemical process in which in situ anodic etching of the substrate surface was performed in the same electrolytic solution as for electroplating of metals (Ni, Au, Sn and Pb). Measurement of the cyclic voltammogram was helpful in determining the applied voltages for in situ etching as well as metal deposition, and thus in fabricating good Schottky contacts reproducibly. The ideality factor (n value) of the fabricated diodes was unity for the substrate with an electron density of 2×1016 cm-3. The values of Schottky barrier heights determined by means of the I-V and C-V methods were in close agreement, and the chemical trend was clearly observed.

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The electrochemical behavior of n-type GaAs(100) was investigated to find an optimum condition for in situ surface treatment in Ni salt electrolytes prior to the fabrication of Ni/GaAs Schottky contacts by the wet method. Commercial machine-polished GaAs wafers with damaged crystal lattices did not show photoresponse and behaved exactly the same as a Ga metal electrode in the region of -0.1 to +0.5 V vs. Ag/AgC1. Photoresponse was observed after the removal of the damaged surface layer in H2SO4-H202-H20. The in situ surface treatment of GaAs was done by photoelectrochemical etching at +0.1 V in acidic nickel salt electrolyte followed by the fabrication of a GaAs/Ni Schottky contact by applying negative potentials. Comparison of the fabrication methods is summarized in a table. The wet method is recommended for the fabrication of a Ni/GaAs Schottky contact.Although Schottky contacts are used in various electronic devices, the barrier heights generally do not agree with the values obtained from the difference between work functions of semiconductors and metals which are in contact with semiconductors. 1 This is partly explained by the formation of surface states by the heat of condensation of evaporating metal molecules. ~We employed a new, wet method for the fabrication of a Schottky contact so as to suppress the formation of surface states at the semiconductor lattice. ~' 4 To date, wet methods have been used for different purposes, e.g., microfabrication of metal electrode, laser-induced deposition of metals, and so on. ~-1~ We expect that the wet process is suitable for low-energy deposition of metals on semiconductors without damaging the surface crystal lattice. Furthermore, electrolysis is effective for the in situ surface treatment of a semiconductor. The surface treatment of GaAs has been carried out with chemical etching in H2SO4-H202-H20 or other solutions leaving oxide films which may induce undesirable electronic behavior. In this paper, we report in situ preparation of oxide-less n-type GaAs surface with photoelectrochemical reaction in metal salt electrolytes.In electrolyte, n-type GaAs produces holes by the illumination of light because a potential barrier exists at the GaAs/electrolyte interface. As a result, anodic photocurrent flows. 5"6 For the GaAs covered with the thick oxide films, however, holes cannot be produced sufficiently and anodic photocurrent scarcely flows. Generally, the photogenerated holes react with chemical species in electrolytes: in alkaline electrolytes, they react with OH-ions 16'17 and in acidic electrolytes, with H20. The reaction with H20 produces hydrated species of Ga and As. At high electric field, they transform to Ga and As oxides as a result of deprotonation and dehydration. However, at low electric field and high concentration of H +, the reactions do not proceed completely, leaving Ga and As as unstable, soluble compounds which further change to more soluble compounds with the reaction of CI-anions in the electrolyte. For sufficient photoelectrochemical dissoluti...