The structure and chemistry of clean GaN surfaces and InGaN thin films and nanostructures grown by metal organic vapour pressure epitaxy (MOVPE) has been studied by means of X-ray photoemission spectroscopy, low-energy electron diffraction as well as scanning tunneling microscopy (STM) and transmission electron microscopy. Thermal annealing strongly improves the cleanliness of samples after dry nitrogen transfer and related exposure to residual oxygen. Nitrogen plasma assisted cleaning is shown to successfully further remove carbon contaminations, while Ga deposition with subsequent desorption to is shown to be superior for an enhanced reduction of surface oxygen. Using STM, the surface morphology has been studied in dependence on major growth parameters at various stages of InGaN MOVPE growth. The formation of nano-islands is reported for different growth conditions. By means of microphotoluminescence measurements, we find samples to show strong photoluminescence from quantum-dot-like structures, however, the corresponding growth front is found to be rather flat throughout InGaN deposition. This leads to the conclusion that the formation of quantum dots does not proceed in a Stranski-Krastanov-like fashion but most likely during overgrowth.Scanning tunneling micrograph and height profile of 3.9 nm InGaN grown by MOVPE at 700 8C, after growth interruption and 1 min post-growth annealing at the growth temperature. The surface exhibits a two-dimensional islands morphology.

Articles you may be interested inSurface oxidation of GaN(0001): Nitrogen plasma-assisted cleaning for ultrahigh vacuum applications J. Vac. Sci. Technol. A 32, 051401 (2014); 10.1116/1.4886956 High quality single atomic layer deposition of hexagonal boron nitride on single crystalline Rh(111) four-inch wafers Rev. Sci. Instrum. 85, 035101 (2014); 10.1063/1.4866648 Preparation and atomic structure of reconstructed (0001) InGaN surfaces J. Appl. Phys. 112, 033509 (2012); 10.1063/1.4743000Preparation and characterization of atomically clean, stoichiometric surfaces of n-and p-type GaN (0001) The cleaning of GaN͑2110͒ surfaces was investigated by x-ray photoelectron spectroscopy, scanning tunneling microscopy, and low-energy electron diffraction. Two different two-step cleaning methods, performed under ultrahigh-vacuum conditions, were carried out and compared. The first cleaning step of both methods is thermal degassing. The second step is either the deposition of metallic gallium followed by redesorption or an exposure to active nitrogen from a radio frequency nitrogen plasma source. Upon storage in a glovebox ͑N 2 atmosphere͒ and transfer to ultrahigh vacuum under dry nitrogen, carbon and oxygen were identified as the major contaminants. A significant decrease in oxygen and carbon was achieved by thermal degassing at 750°C under ultrahigh-vacuum conditions. By applying a subsequent Ga deposition/redesorption or N 2 -plasma cleaning step, a further reduction in oxygen and carbon could be achieved. In comparison, the Ga deposition/redesorption cleaning showed a better performance in oxygen removal, whereas the N 2 plasma exhibits a better efficiency in carbon removal. Furthermore scanning tunneling microscopy and low-energy electron diffraction investigations showed a drastic improvement of the morphology and atomic structure of the clean surfaces in contrast to the sample surfaces after N 2 storage and transfer.

The ($ \bar 2 $110) plane of gallium nitride, exposed by cleaving a GaN single crystal under ultra‐high vacuum conditions, has been atomically resolved for the first time, using cross‐sectional scanning tunneling microscopy. The spatial period length supports a (1 × 1) unit mesh size, i.e., the absence of a reconstruction. The contrast observed in the experimental data is well explained by the atomic arrangement expected for a truncated‐bulk structure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)