REACTION OF HCL WITH THE GAAS(100) SURFACE

We have studied the interaction of HCl with Ga-rich and As-rich GaAs(1 00) surfaces, using AES, TPD, HREELS, and MQS. HREELS data show that w hen the surface is dosed with H atoms they bond to both As and Ga, but when HCl reacts with the surface the H atoms bond only to As, on both the Ga-rich and As-rich surfaces. Therefore, HCl does not add across Ga dimer bonds on the Ga-rich surface, as is found with Cl-2. A reacti on model is proposed in which HCl adds across Ga-As backbonds at Ga di mer vacancies, with H bonding to As and Cl bonding to Ga. When the sam ple temperature is raised after reacting HCl with GaAs at 85 K, the on ly etch products desorbed are GaCl and As-2. H-2 and HCl are also deso rbed due to combination of surface H and Cl atoms. The TPD data for th e etch products from reaction of HCl versus Cl-2 agree with the observ ations that Cl-2, etches GaAs at temperatures as low as 320 K, whereas etching by HCl requires temperatures above 600 K.