%0 Journal Article %J Materials Research Society Proceedings %D 1997 %T Pressure Controlled GaN MBE Growth Using a Hollow Anode Nitrogen Ion Source %A Michael S.H. Leung %A Ralf Klockenbrink %A Christian F. Kisielowski %A Hiroaki Fujii %A Joachim Krüger %A Sudhir G. Subramanya %A André Anders %A Zuzanna Liliental-Weber %A Michael D. Rubin %A Eicke R. Weber %E Joachim Krüger %X

GaN films were grown on sapphire substrates at temperatures below 1000 K utilizing a Hollow Anode nitrogen ion source. A Ga flux limited growth rate of ~0.5 μm/h is demonstrated. Active utilization of strain and the assistance of a nitrogen partial pressure during buffer layer growth are found to be crucial issues that can improve the film quality. The best films exhibit a full width at half maximum of the x-ray rocking curves of 80 arcsec and 1.85 meV for the excitonic photoluminescence measured at 4 K. A Volmer-Weber three dimensional growth mode and the spontaneous formation of cubic GaN inclusions in the hexagonal matrix are observed in the investigated growth temperature range. It is argued that this growth mode contributes to a limitation of the carrier mobility in these films that did not exceed 120 cm2/Vs through a minimum canier concentration of ~1015 cm-3 was achieved.

%B Materials Research Society Proceedings %V 449 %G eng %N 221 %1

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%2 LBNL-39851 %! MRS Proceedings %R 10.1557/PROC-449-221 %0 Conference Proceedings %B Materials Research Society Symposium N – III-V Nitrides %D 1996 %T Impact of Growth Temperature, Pressure and Strain on the Morphology of GaN Films %A Hiroaki Fujii %A Christian F. Kisielowski %A Joachim Krüger %A Michael S.H. Leung %A Ralf Klockenbrink %A Michael D. Rubin %A Eicke R. Weber %E Joachim Krüger %X

GaN films grown on sapphire at different temperatures are investigated. A Volmer-Weber growth mode is observed at temperatures below 1000K that leads to thin films composed of oriented grains with finite size. Their size is temperature dependent and can actively be influenced by strain. Largest grains are observed in compressed films. It is argued that diffusing Ga ad-atoms dominate the observed effects with an activation energy of 2.3 ± 0.5 eV. Comparably large grain sizes are observed in films grown on off-axes sapphire substrates and on bulk GaN. This assures that the observed size limitation is a consequence of the 3D growth mode and not dependent on the choice of the substrate. In addition, the grain size and the surface roughness of the films depend on the nitrogen partial pressure in the molecular beam epitaxy (MBE) chamber,most likely due to collisions between the reactive species and the background gas molecules. This effect is utilized to grow improved nucleation layers on sapphire.

%B Materials Research Society Symposium N – III-V Nitrides %V 449 %P 227 %G eng %1

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%2 LBNL-39850 %R 10.1557/PROC-449-227 %0 Conference Paper %B 23rd International Conference on the Physics of Semiconductors %D 1996 %T Origin of Strain in GaN Thin Films %A Christian F. Kisielowski %A Joachim Krüger %A Michael S.H. Leung %A Ralf Klockenbrink %A Hiroaki Fujii %A Tadeusz Suski %A Sudhir G. Subramanya %A Joel W. Ager III %A Michael D. Rubin %A Eicke R. Weber %E Joachim Krüger %X

Photoluminescence measurements are used to determine the strain in GaN thin films grown by Molecular Beam Epitaxy. The strain which originates from growth on lattice mismatched substrates and from differences in thermal expansion coefficients is found to be greatly relaxed. Residual strains are shown to depend on the thickness of GaN buffer layers and the III/V flux ration during main layer growth. The results strongly suggest that the residual biaxial strain caused by the post-growth cooling can be modified by the incorporation of point defects during the main layer growth which introduce an additional hydrostatic strain field. The effect allows for strain engineering of GaN crystals.

%B 23rd International Conference on the Physics of Semiconductors %C Singapore %V 4 %P 513 %G eng %L LBNL-39853 %1

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%2 LBNL-39853