Composition and structure of the GaN{0001}-(1x1) surface

The composition and structure of the n-type GaN{<000(1)over bar>}-(1x1) surface of samples grown on sapphire by organometallic vapor-phase epitaxy (OMVPE) has been determined through the use of time-of-flight scattering and recoiling spectrometry (TOE-SAPS), three-dimensional classical ion trajectory simulations, low-energy electron diffraction (LEED), and thermal decomposition mass spectrometry (MS). Elastic recoil detection was used to determine the bulk hydrogen concentration. TOF-SARS spectra of scattered and recoiled ions plus fast neutrals were collected as a function of crystal azimuthal rotation angle delta and beam incident angle alpha using 4 keV Ne+ or Ar+ primary ions in order to determine the surface termination layer, presence and location of impurities, and possible reconstruction or relaxation. LEED, TOF-SARS, and MS were monitored as a function sample temperature up to the point of decomposition. The totality of these data leads to the conclusions that the (1x1) surface is neither reconstructed nor relaxed, that it is terminated in a N layer, that Ga comprises the second layer, that there are two domains rotated by 60 degrees from each other, and that there are steps on the surface. Hydro en atoms are bound to the outerlayer N atoms and protrude outward from the surface with of similar to 3/4 a coverage monolayer, facilitating autocompensation of the (1x1) structure. The bulk hydrogen concentration is similar to 4x10(19) atoms/cm(3). Evolution of gases commences at similar to 850 degrees C with the observed evolution of N-2, NH2, and H-2. These results are discussed in terms of reconstruction phenomena, autocompensation, film/substrate polarity matching, and the role of hydrogen in stabilizing the growth of GaN.