REACTION OF HCL WITH THE GAAS(100) SURFACE

We have studied the interaction of HCl with Ga-rich and As-rich GaAs(100) surfaces, using AES, TPD, HREELS, and MQS. HREELS data show that when 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 reaction model is proposed in which HCl adds across Ga-As backbonds at Ga dimer vacancies, with H bonding to As and Cl bonding to Ga. When the sample temperature is raised after reacting HCl with GaAs at 85 K, the only etch products desorbed are GaCl and As-2. H-2 and HCl are also desorbed due to combination of surface H and Cl atoms. The TPD data for the etch products from reaction of HCl versus Cl-2 agree with the observations that Cl-2, etches GaAs at temperatures as low as 320 K, whereas etching by HCl requires temperatures above 600 K.