GaAs, a compound semiconductor commonly used in optoelectronic
devices, is often subjected
to wet-etching techniques during microelectronic device manufacture.
In this work we
investigated the wet etching of GaAs by
H2O2−NH4OH−H2O
solutions using a batch stirred-tank reactor and determined the intrinsic kinetics of the dissolution
reaction. Increasing the
NH4OH content produced a constant rate above a minimum
concentration. The reaction rate
was found, in the presence of excess NH4OH, to fit a
rate equation r =
k[H2O2]0.75 at 15, 25,
and
40 °C with an activation energy of 33.7 kJ/mol. Using NaOH
instead of NH4OH resulted in
greatly reduced reaction rates, and it was concluded that the presence
of the ammonium ion
increases the rate by forming soluble compounds with oxidized species
of Ga and As. Analysis
of the surface by X-ray photon spectroscopy confirmed that samples
etched in solutions containing
NH4OH had considerably less oxide content on the
surface than that etched in
H2O2−H2O only.
NH4OH does not directly react with GaAs but
incorporates a second step into the overall etch
reaction, facilitating the oxidation by H2O2
and the formation of soluble compounds.
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