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The adsorption of hydrogen at nonpolar GaN(1-100) surfaces and its impact onthe electronic and vibrational properties is investigated using surfaceelectron spectroscopy in combination with density functional theory (DFT)calculations. For the surface mediated dissociation of H2 and the subsequentadsorption of H, an energy barrier of 0.55 eV has to be overcome. Thecalculated kinetic surface phase diagram indicates that the reaction iskinetically hindered at low pressures and low temperatures. At highertemperatures ab-initio thermodynamics show, that the H-free surface isenergetically favored. To validate these theoretical predictions experiments atroom temperature and under ultrahigh vacuum conditions were performed. Theyreveal that molecular hydrogen does not dissociatively adsorb at the GaN(1-100)surface. Only activated atomic hydrogen atoms attach to the surface. Attemperatures above 820 K, the attached hydrogen gets desorbed. The adsorbedhydrogen atoms saturate the dangling bonds of the gallium and nitrogen surfaceatoms and result in an inversion of the Ga-N surface dimer buckling. Thesignatures of the Ga-H and N-H vibrational modes on the H-covered surface haveexperimentally been identified and are in good agreement with the DFTcalculations of the surface phonon modes. Both theory and experiment show thatH adsorption results in a removal of occupied and unoccupied intragap electronstates of the clean GaN(1-100) surface and a reduction of the surface upwardband bending by 0.4 eV. The latter mechanism largely reduces surface electrondepletion.

Adsorption and desorption of hydrogen at nonpolar GaN(1-100) surfaces: Kinetics and impact on surface vibrational and electronic properties