A Study of Hydrogen Atom Adsorption on Gallium Arsenide (100) by Multiple Internal Reflection Infrared Spectroscopy

We have studied the adsorption of hydrogen atoms on GaAs (100) by multiple internal reflection infrared spectroscopy. The crystal was etched in 1:1:10 H3PO4/H2O2-/H2O solution and in 1:1 HCI/H2O solution, then annealed to 580°C in the vacuum chamber. Hydrogen adsorption was carried out at −90 and 45°C. At both temperatures, a monolayer forms giving rise to infrared bands for arsenic hydride and gallium hydride at 2105 and 1860 cm−1, respectively. The arsenic hydride vibration is polarized parallel to the surface, whereas the gallium hydride vibration is polarized normal to the surface. By monitoring the changes in the intensity of the infrared absorption bands with time during exposure to H atoms and during heating, the kinetics of hydrogen adsorption and desorption can be measured. At t`9°C, the H atom sticking probability follows the Langmuir model, $$S/{S_ \circ } = (1 - {\theta _H})$$ . Upon heating the crystal, the arsenic hydride rapidly decomposes near 120°C, while the gallium hydride slowly decomposes between 150 and 400°C.