Hydrogen adsorption on GaAs(110) studied by temperature-programmed desorption

GaAs(110) was cleaved in ultrahigh vacuum and exposed to atomic and to molecular hydrogen. After exposure at 250 K to molecular hydrogen neither H nor ${\mathrm{H}}_2$ is found desorbing up to 670 K. Upon adsorption of atomic hydrogen, use of the temperature-programmed-desorption technique reveals a second-order process for the desorption of molecular hydrogen ($E_d=13.8\mathrm{}$ kcal/mole, $T_{max}$ near 450 K), with no desorption of atomic hydrogen. Desorption of As${\mathrm{H}}_3$ ($T_{max}=340\mathrm{}$ K) precedes the desorption of ${\mathrm{H}}_2$. Further H chemisorption induces an additional amount of Ga atoms to desorb above 700 K. Preadsorption of hydrogen decreases the ${\mathrm{As}}_2$ evaporation rate. An energy scheme with the equilibrium and an excited adsorbate state is derived from the combination of the temperature-programmed-desorption data and the high-resolution electron-energy-loss spectroscopy data of Lüth and Math [Phys. Rev. Lett. 46, 1652 (1981)].