InN and InGaN alloys still belong to the least understood materials among the group III-nitrides. However, due to the promising applications, e.g. blue, green and infrared light emitters, solarcells and high frequency transistors it is crucial to obtain more information on the atomic surface structure, binding configuration and electronic properties such as surface charge accumulation and band bending. Furthermore, the existence of metallic bilayers has been proposed recently, which require more detailed investigation [1].

In_xGa_1-xN layers with different In-content (0.07<x<0.3) and film thicknesses ranging between 15nm and 30nm were grown by metallorganic vapour phase epitaxy (MOVPE) on (0001) GaN/sapphire. Within this work the preparation of clean surfaces was investigated by annealing the In_xGa_1-xN samples under ultrahigh vacuum (UHV) conditions at temperatures between 350°C and 800°C and the results are compared to results obtained on 300nm thick InN films on sapphire substrate. The stoichiometry, atomic structure and binding configuration were elucidated with Atomic Force Microscopy (AFM), Electron Energy Diffraction methods (LEED, RHEED), Scanning Tunneling Microscopy (STM), Auger Electron Spectroscopy (AES) and Synchrotron based Photoemission Spectroscopy (SXPS).

The post-growth surface morphology was determined by AFM and reveals a surface roughness of approximately 2nm for InGaN (15% In-content) and 25nm for InN. Also typical defects like screw dislocations and surface pits can be observed. After transfer into UHV the samples were thermally deoxidized by radiative heating. AES and SXPS measurements of the chemical surface composition confirm residual oxide components such as carbon and oxygen even after annealing up to 600°C on both, InN and InGaN.  The surface symmetry as observed by RHEED and LEED reveals a (1x1) pattern and does not change during these annealing steps. However, further annealing of InGaN at higher temperatures leads to a strong reduction of carbon and oxygen and a change of the diffraction pattern. LEED measurements reveal clearly a (1+1/6)-surface periodicity as reported for GaN(0001) in [2]. Depending on the preparation conditions a (2x2) symmetry can be observed. STM images on such prepared clean surfaces show atomically flat terraces. Annealing at higher temperatures leads to a destructive change of the surface morphology and chemical composition. Further, LEED reveals faceting structures on the surface.

[1] T.D. Veal et al., Phys. Rev. B 76 (2007) 075313

[2] A.R. Smith et al., J. Vac. Sci. Technol. B. 16 (1998) 2242

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