Investigation of the mechanism of Ar+ ion-assisted Cl2 etching of GaAs{110}: Role of ion-induced charge acceptor states

An investigation of the Ar+ ion-assisted Cl2/GaAs{110} etching reaction mechanism is presented. Using modulated supersonic beam scattering and time-of-flight techniques we have measured the intensity and kinetic energy of the unreacted Cl2 and the dominant Ga-containing reaction product as a function of ion dose and surface temperature. Ion-enhanced reactivity is demonstrated and evidence that the ion-assisted GaCl2 etch product is desorbed by a physical momentum transfer mechanism is given. Surface stoichiometric and chemical state changes have been recorded as a function of etch parameters using in situ x-ray photoelectron spectroscopy. A significant dependence of the post-etch surface composition on the Ar+/Cl2 flux ratio is found ranging from Ga-rich under high Ar+ flux conditions to As-rich under high Cl2 flux conditions. These observations indicate a strong dependence of the relative As to Ga product desorption rates on the reaction parameters. From core level and valence band binding energy measurements we have identified important ion-induced band bending effects that indicate the formation of midgap charge acceptor states. The implication of these results on the ion-assisted etch mechanism is discussed.