Raman scattering of coupled longitudinal optical phonon-plasmon modes in dry etched <i>n</i>+-GaAs

We have carried out extensive Raman scattering investigations of the damage caused by the dry etching in GaAs. The heavily doped n+-GaAs (2–3×1018 cm−3) allows the study of the coupled longitudinal optical (LO) phonon-plasmon mode as a probe to assess the dry etch-induced damage. Three etching techniques were used including conventional radio frequency (rf) reactive ion etching (RIE), ion beam etching (IBE), and electron cyclotron resonance radio frequency reactive ion etching (ECR-RIE). It is demonstrated that the etched damage is confined to a few tens of nanometers after 20 nm of material is etched away. ECR-RIE etching produces the smallest damage. It is found that in RIE etching, as etching proceeds, the depletion depth saturates while for purely physical etching (IBE) the depletion depth increases continuously, at least under the conditions used.