TY - JOUR T1 - Pressure Controlled GaN MBE Growth Using a Hollow Anode Nitrogen Ion Source JF - Materials Research Society Proceedings Y1 - 1997/ A1 - Michael S.H. Leung A1 - Ralf Klockenbrink A1 - Christian F. Kisielowski A1 - Hiroaki Fujii A1 - Joachim Krüger A1 - Sudhir G. Subramanya A1 - André Anders A1 - Zuzanna Liliental-Weber A1 - Michael D. Rubin A1 - Eicke R. Weber ED - Joachim Krüger AB - 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. VL - 449 IS - 221 N1 -

1996 MRS Fall Meeting

U1 -

Windows and Daylighting Group

U2 - LBNL-39851 JO - MRS Proceedings DO - 10.1557/PROC-449-221 ER - TY - Generic T1 - Impact of Growth Temperature, Pressure and Strain on the Morphology of GaN Films T2 - Materials Research Society Symposium N – III-V Nitrides Y1 - 1996/ SP - 227 A1 - Hiroaki Fujii A1 - Christian F. Kisielowski A1 - Joachim Krüger A1 - Michael S.H. Leung A1 - Ralf Klockenbrink A1 - Michael D. Rubin A1 - Eicke R. Weber ED - Joachim Krüger AB - 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. JF - Materials Research Society Symposium N – III-V Nitrides VL - 449 U1 -

Windows and Daylighting Group

U2 - LBNL-39850 DO - 10.1557/PROC-449-227 ER - TY - CONF T1 - Origin of Strain in GaN Thin Films T2 - 23rd International Conference on the Physics of Semiconductors Y1 - 1996/ SP - 513 A1 - Christian F. Kisielowski A1 - Joachim Krüger A1 - Michael S.H. Leung A1 - Ralf Klockenbrink A1 - Hiroaki Fujii A1 - Tadeusz Suski A1 - Sudhir G. Subramanya A1 - Joel W. Ager III A1 - Michael D. Rubin A1 - Eicke R. Weber ED - Joachim Krüger AB - 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. JF - 23rd International Conference on the Physics of Semiconductors CY - Singapore VL - 4 U1 -

Windows and Daylighting Group

U2 - LBNL-39853 ER - TY - JOUR T1 - Strain Related Phenomena in GaN Thin Films JF - Physical Review B Y1 - 1996/12// SP - 17745 EP - 17753 A1 - Christian F. Kisielowski A1 - Joachim Krüger A1 - Sergei Ruvimov A1 - Tadeusz Suski A1 - Joel W. Ager III A1 - Erin C. Jones A1 - Zuzanna Liliental-Weber A1 - Michael D. Rubin A1 - Eicke R. Weber A1 - Michael D. Bremser A1 - Robert F. Davis ED - Joachim Krüger AB - Photoluminescence (PL), Raman spectroscopy, and x-ray diffraction are employed to demonstrate the co-existence of a biaxial and a hydrostatic strain that can be present in GaN thin films. The biaxial strain originates from growth on lattice-mismatched substrates and from post-growth cooling. An additional hydrostatic strain is shown to be introduced by the presence of point defects. A consistent description of the experimental results is derived within the limits of the linear and isotropic elastic theory using a Poisson ratio nu =0.23+/-0.06 and a bulk modulus B=200+/-20 GPa. These isotropic elastic constants help to judge the validity of published anisotropic elastic constants that vary greatly. Calibration constants for strain-induced shifts of the near-band-edge PL lines with respect to the E2 Raman mode are given for strain-free, biaxially strained, and hydrostatically contracted or expanded thin films. They allow us to extract differences between hydrostatic and biaxial stress components if present. In particular, we determine that a biaxial stress of one GPa would shift the near-band-edge PL lines by 27+/-2 meV and the E2 Raman mode by 4.2+/-0.3 cm-1 by use of the listed isotropic elastic constants. It is expected from the analyses that stoichiometric variations in the GaN thin films together with the design of specific buffer layers can be utilized to strain engineer the material to an extent that greatly exceeds the possibilities known from other semiconductor systems because of the largely different covalent radii of the Ga and the N atom. VL - 54 IS - 24 U1 -

Windows and Daylighting Group

U2 - LBNL-39079 DO - 10.1103/PhysRevB.54.17745 ER - TY - JOUR T1 - The Influence of Nitrogen Ion Energy on the Quality of GaN Films Grown with Molecular Beam Epitaxy JF - Journal of Electronic Materials Y1 - 1995/04// SP - 249 EP - 255 A1 - T.C. Fu A1 - Nathan Newman A1 - Erin C. Jones A1 - James S. Chan A1 - Xiaohong Liu A1 - Michael D. Rubin A1 - Nathan W. Cheung A1 - Eicke R. Weber KW - Activated nitrogen KW - GaN KW - molecular beam epitaxy (MBE) KW - nitrogen ion energy AB - Since the growth of GaN using molecular beam epitaxy (MBE) occurs under metastable growth conditions, activated nitrogen is required to drive the forward synthesis reaction. In the process of exciting the nitrogen using a plasma or ion-beam source, species with large kinetic energies are generated. Impingement on the growth surface by these species can result in subsurface damage to the growing film, as well as an enhancement of the reverse decomposition reaction rate. In this study, we investigate the effect of the kinetic energy of the impinging nitrogen ions during growth on the resulting optical and structural properties of GaN films. Strong band-edge photoluminescence and cathodoluminescence are found when a kinetic energy of ~10 eV are used, while luminescence is not detectable when the kinetic energies exceeds 18 eV. Also, we find that the use of conductive SiC substrates results in more homogeneous luminescence than the use of insulating sapphire substrates. This is attributed to sample surface charging in the case of sapphire substrates and subsequent variation in the incident ion flux and kinetic energy across the growth surface.This study clearly shows that the quality of GaN films grown by MBE are presently limited by damage from the impingement of high energy species on the growth surface. VL - 24 IS - 4 U1 -

Windows and Daylighting Group

U2 - LBL-37223 DO - 10.1007/BF02659683 ER - TY - JOUR T1 - Thermal Annealing Characteristics of Si and Mg-implanted GaN Thin Films JF - Applied Physics Letters Y1 - 1996/03// SP - 2702 EP - 2704 A1 - James S. Chan A1 - Nathan W. Cheung A1 - Lawrence F. Schloss A1 - Erin C. Jones A1 - William S. Wong A1 - Nathan Newman A1 - Xiaohong Liu A1 - Eicke R. Weber A1 - A. Gassman A1 - Michael D. Rubin KW - annealing KW - crystal doping KW - defect states KW - electrical properties KW - gallium nitrides KW - ion implantation KW - magnesium additions KW - microstructure KW - silicon additions AB - In this letter, we report the results of ion implantation of GaN using 28Si and 23Mg species. Structural and electrical characterizations of the GaN thin films after thermal annealing show that native defects in the GaN films dominate over implant doping effects. The formation energies of the annealing induced defects are estimated to range from 1.4 to 3.6 eV. A 30 keV10^14 cm-2 Mg implant results in the decrease of the free-carrier concentration by three orders of magnitude compared to unimplanted GaN up to an annealing temperature of 690 °C. Furthermore, we have observed the correlation between these annealing-induced defects to both improved optical and electrical properties. VL - 68 IS - 19 U1 -

Windows and Daylighting Group

U2 - LBL-37372 DO - 10.1063/1.116314 ER - TY - CONF T1 - Fundamental Materials-Issues Involved in the Growth of GaN by Molecular Beam Epitaxy Y1 - 1994/ A1 - Nathan Newman A1 - T.C. Fu A1 - Z. Liu A1 - Zuzanna Liliental-Weber A1 - Michael D. Rubin A1 - James S. Chan A1 - Erin C. Jones A1 - Jennifer T. Ross A1 - Ian M. Tidswell A1 - Kin Man Yu A1 - Nathan W. Cheung A1 - Eicke R. Weber AB - Gallium nitride is one of the most promising materials for ultraviolet and blue light-emitting diodes and lasers. Both Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD) have recently made strong progress in fabricating high-quality epitaxial GaN thin films. In this paper, we review materials-related issues involved in MBE growth. We show that a strong understanding of the unique meta-stable growth process allows us to correctly predict the optimum conditions for epitaxial GaN growth. The resulting structural, electronic and optical properties of the GaN films are described in detail. U2 - LBL-37296 ER -