In Situ Surface Treatment of GaAs ( 100 )  Wafer in Metal Salt Electrolytes for Fabrication of Schottky Contact

Abstract

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...

Electroreduction of Co2 + and Ni2 + at III-V Semiconductors and Properties of the Semiconductor/Metal Interfaces Formed

“…14,15 It has to be remarked that in the latter case, the authors were unable to explain the large difference between ⌽ B jV and ⌽ B CV . When comparing the measured values of the barrier height of the junctions formed in this work with literature values of electrochemically formed n-GaAs/ Ni contacts, it appears that the barriers formed between Ϫ1.2 and Ϫ1.3 V vs. SCE are somewhat lower: in the literature values for ⌽ B jV between 0.78 and 0.81 eV 4,8,9 and for ⌽ B CV between 0.82 and 0.86 eV 4,9 have been reported.…”

“…In the literature, very little information is available about the characteristics of n-GaP/Co barriers formed by ultrahigh vacuum (UHV) deposition, 13 whereas electrodeposition from cobalt ion solutions upon GaP has to our knowledge not been performed yet. In the case of n-GaAs/Co as well as of n-GaAs/Ni dry junctions on the other hand, it appeared that the barrier was higher for electrochemically formed barriers 4,9 than for barriers made by UHV deposition. 14,15 However, a systematic study on the electrochemical reduction processes at n-and a p-type GaAs single crystals has not been performed yet.…”

“…It has been demonstrated that the formation of Schottky barriers by electrochemical deposition may lead to interfaces with characteristics which are comparable to or even better than those formed by dry methods. [2][3][4][5][6][7][8][9][10][11][12] Furthermore, electrodeposition from a metal salt in solution has the advantage that the process itself is better defined: the semiconductor surface can be controlled by varying the solution composition or the deposition potential. Another advantage is that in situ pretreatment of the surface is possible.…”

“…Another advantage is that in situ pretreatment of the surface is possible. 9 This paper pertains to a study which we have performed on the electroreduction of Ni 2ϩ and Co 2ϩ ions at n-and p-type GaAs and GaP electrodes and on the electrochemical formation of n-GaP/Co, n-GaAs/Co, and n-GaAs/Ni interfaces. In the literature, very little information is available about the characteristics of n-GaP/Co barriers formed by ultrahigh vacuum (UHV) deposition, 13 whereas electrodeposition from cobalt ion solutions upon GaP has to our knowledge not been performed yet.…”

Nanoscale etching of GaAs surfaces in electrolytic solutions by hole injection from a scanning tunneling microscope tip

“…We have investigated the electrochemical and photoelectrochemical properties of n-GaAs in the electrolytic solution. [10][11][12] The rate of oxide formation of n-GaAs in acidic solutions of pHϭ2, which were used in the present study, is larger than the dissolution rate of the formed oxides when the applied potential became more anodic level than ϩ0.1 V vs Ag/AgCl. In this case, it is difficult to take a STM image since the surface is covered with the thin oxide films.…”