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

The composition and structure of the n-type GaN{0001¯}-(1×1) 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 (TOF-SARS), 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 δ and beam incident angle α using 4 keV ${\mathrm{Ne}}^{+}$ or ${\mathrm{Ar}}^{+}$ 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 (1×1) 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° from each other, and that there are steps on the surface. Hydrogen atoms are bound to the outerlayer N atoms and protrude outward from the surface with a coverage of ∼3/4 monolayer, facilitating autocompensation of the (1×1) structure. The bulk hydrogen concentration is ∼4×${10}^{19}$ atoms/${\mathrm{cm}}^3$. Evolution of gases commences at ∼850 °C with the observed evolution of ${\mathrm{N}}_2$, ${\mathrm{NH}}_2$, and ${\mathrm{H}}_2$. 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. © 1996 The American Physical Society.