Desorption of hydrogen from GaN(0001) observed by HREELS and ELS

Abstract

The bare and hydrogenated GaN(0001) surfaces were characterized using high resolution electron energy loss spectroscopy (HREELS), electron energy loss spectroscopy (ELS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). AES and LEED show that the GaN surface is clean but faceted. Changes in the surface electronic structure are characterized using ELS. Exposure to atomic hydrogen produces a merging of the double peak centered near 20 eV and a leveling of the region from 10 to 15 eV. These hydrogen-induced changes begin to decrease after briefly heating to 260°C and are completely reversed after heating to 380°C. Atomic hydrogen exposure produces HREELS loss peaks at 2580, 3280 and 3980 cm −1 due to combinations of the Ga–H stretching vibration at 1880 cm −1 and Fuchs–Kliewer phonons. Briefly heating to 260°C or above produces a decrease in the intensity of Ga–H vibrations. Heating to 380°C results in a complete disappearance of adsorbate vibrational peaks. Observation of desorbing molecular hydrogen by mass spectrometry confirms that the disappearance of Ga–H features in HREEL and ELS spectra is due to recombinative desorption of hydrogen. Overall this work demonstrates desorption of hydrogen from surface Ga sites between 250 and 450°C.