GaAs surface cleaning by low-energy hydrogen ion bombardment at moderate temperatures

Abstract

Low-energy hydrogen ion beam treatment is used to remove contaminations of carbon and oxygen from gallium arsenide (GaAs) surfaces. Real time spectroscopic ellipsometry is utilized to monitor the time evolution of the in situ ellipsometric parameters ⟨ε1⟩ and ⟨ε2⟩ during exposure of GaAs surfaces to inert H2 molecules, hydrogen plasma radicals, and hydrogen ions with energies up to Eion=400eV. Model analysis of the ellipsometric data allows the determination of both, the oxide layer degradation and the hydrogen-induced dielectric function alteration of GaAs. The degradation of the oxide layer as well as the changes of the dielectric function of GaAs depends on the surface temperature and hydrogen ion energy. Ellipsometry reveals oxygen clean surfaces for hydrogen ion bombardment with an energy of Eion=300eV at temperatures as low as 150°C, which is confirmed by in situ x-ray photoelectron spectroscopy measurements. The incorporation behavior of hydrogen and therefore the dielectric function alteration depends on the doping type of GaAs. In hydrogen-modified semi-insulating GaAs the observed energy redshift of the critical points E1 und E1+Δ1 is mainly caused by the increase of the intrinsic stress level, whereas in p-type GaAs additionally surface band bending effects are responsible for the change of the dielectric function of GaAs.