The Electrochemical Nature of GaAs in Acids: A Comparison with InP

Abstract

The chemical composition of surface oxides grown on GaAs was investigated using x-ray diffraqtion techniques. Native oxides were prepared by exposing the GaAs to HCI and HNO3 etchants at concentrations ranging from pH 5 to the maximum acidities available. A mixture of crystalline stoiehiometric phases were formed. The chemical oxides appear to be more complex than indicated by previous studies by x-ray photoelectron spectroscopy, but were independent of the type of etchant or its acidity. Only constituent oxides, rather than mixed oxides, were found on the oxidized GaAs surface. The thermodynamics may play a key role in the reaction pathway. In the HCI etch, Ga ~ and GaLGa m ehloro compounds are not formed, and the dissolution of GaAs is severely inhibited even in the most acidic solutions under illumination. This complete absence of nucleophilic attack of the Ga--As bond by a CI-ion is reasonably well explained by the fact that the intermediate, GaCI, is not thermodynamically stable.

The Mechanism of Hydrogen Gas Evolution on GaAs Cathodes Elucidated by In Situ Infrared Spectroscopy

“…Elemental arsenic is thermodynamically stable in deaerated solutions at any pH, but residual oxygen oxidizes arsenic, and surface oxides on elemental arsenic are orders of magnitude more soluble at pH 14 than at pH 0 . This would explain observations that (photo)anodic treatment yields a porous arsenic layer in acidic solution, ,− whereas elemental arsenic is removed in alkaline solution. ,− The observation of an atomically flat (100) face by AFM in 10 mM H 2 SO 4 46 demonstrates that GaAs surfaces in the dark are relatively stable in oxygen-free solutions. In oxygenated solutions of 1 to 12 M HCl, the chemical dissolution rate of GaAs is what one would expect on the basis of oxidation by dissolved oxygen …”

“…54 This would explain observations that (photo)anodic treatment yields a porous arsenic layer in acidic solution, 11,[56][57][58][59] whereas elemental arsenic is removed in alkaline solution. 56,[60][61][62][63] The observation of an atomically flat (100) face by AFM in 10 mM H 2 SO 4 46 demonstrates that GaAs surfaces in the dark are relatively stable in oxygen-free solutions. oxygenated solutions of 1 to 12 M HCl, the chemical dissolution rate of GaAs is what one would expect on the basis of oxidation by dissolved oxygen.…”

“…oxygenated solutions of 1 to 12 M HCl, the chemical dissolution rate of GaAs is what one would expect on the basis of oxidation by dissolved oxygen. 63…”

Fabrication of microrods and microtips of InP by electrochemical etching

“…Hsieh et al [13] presented the synergism effects between Cl À ions and photons in strong HCl solutions. And the formation of In III and In I mixed valence compounds and In I chloro compounds had been confirmed [22]. The dissolution rate of InP may be enhanced due to the presence of the Cl À ions, which means that the Cl À ions take part in the dissolution of indium and the formation of the In III via an In I chloro intermediate.…”

The etching behavior of n-GaP in aqua regia solutions

“…X-ray wide angle diffraction (WAD) and glancing angle diffraction (GAD) techniques have been used in our previous studies [7][8][9][10][11][12][13] to establish a much better understanding of the chemical nature of GaP, [7][8][9] GaAs, [10,11] and InP [12][13][14]surfaces after a variety of chemical treatments. In previous work, [7][8][9] the dissolution mechanisms of n-GaP in HNO 3 and in HCl have been investigated, respectively.…”