Gallium Arsenide (GaAs) Etchants

As a III/V semiconductor, gallium arsenide (GaAs) is used for high technology applications such as electronics, optics, photovoltaics, lasers as well as defense and aerospace applications. Like silicon, GaAs wet etching proceeds via the formation of an oxide, or oxides, on the surface followed by dissolution of the oxidized products by either acids or bases. Ga is already in the oxide form (Ga₂O₃); however, As, being an  arsenide (As^-3), should be oxidized (e.g., H₂O₂) first to form the soluble oxide. The following depicts the As and Ga chemical reactions:

2As₃^– + 6H₂O₂ + H⁺ => As₂O₃ + 5OH^– + 4H₂O

2Ga³⁺ + 6OH^– => 2Ga(OH)₃

Since the surface activity of the As (+3) and Ga (+3) are very different, the etchants are not typically isotropic. The As rich face being significantly more reactive (e.g., two unsatisfied bonds per atom) than the Ga rich face (e.g., no unsatisfied bond per atom) will etch faster under identical conditions. This leads to a more polished As surface while the Ga face tends to appear hazy/frosted due to the more visible surface features and crystallographic defects.

The important considerations for choosing the right etch chemistries are listed below:

• Acidic vs basic oxidation condition
• Isotropic vs anisotropic etch
• The underlying etch-stop layer composition
• Film thickness
• Acid viscosity and concentration
• Diffusion vs reaction-rate limited etching
• Etch-defined edge definition
• Etch selectivity vs etchant mix ratio/concentration
• Etchant aging vs compositional change
• Etch temperature vs etch rate
• Smooth vs rough GaAs and etch-stop layer surfaces

Solexir GaAs etch offerings are highlighted in the following table:

For product recommendation and technical support, please contact Solexir