Dry etching induced damage on vertical sidewalls of GaAs channels

Abstract

Damage on the vertical sidewalls of narrow GaAs structures has been investigated. The structures consisted of narrow conducting channels between Ohmic pads. The channels were defined by either masked ion beam lithography or electron beam lithography with channel widths varying from 0.08 to 1.5 μm. Reactive ion etching and ion beam assisted etching were used to remove the epitaxial material outside the channels down to the semi-insulating substrates. Conduction in the channels was monitored by measuring current–voltage characteristics between the Ohmic pads. It is found that saturation current depends on the dry etching conditions such as ion energy, etching species, and impurity redeposition. Ion beam etching of GaAs substrates at different angles was used to separate out the effects of the inert ion species of reactive ion etching and ion beam assisted etching. Large increases in leakage current and impurity concentrations were obtained when the sample was mounted in the plane parallel to the direction of the ion beam, indicating that redeposition from fixtures and chamber walls can be significant. Controllable etching with minimal damage in GaAs is obtained by using low ion energy, reactive gases, and a contamination-free environment in the chamber. By optimizing the etching conditions, conduction was observed for channels with mirror-smooth sidewalls and widths as small as 0.08 μm.