%0 Journal Article %J Physical Review B %D 1996 %T Strain Related Phenomena in GaN Thin Films %A Christian F. Kisielowski %A Joachim Krüger %A Sergei Ruvimov %A Tadeusz Suski %A Joel W. Ager III %A Erin C. Jones %A Zuzanna Liliental-Weber %A Michael D. Rubin %A Eicke R. Weber %A Michael D. Bremser %A Robert F. Davis %E Joachim Krüger %X

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.

%B Physical Review B %V 54 %P 17745-17753 %8 12/1996 %G eng %N 24 %1

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%2 LBNL-39079 %& 17745 %R 10.1103/PhysRevB.54.17745 %0 Journal Article %J Journal of Electronic Materials %D 1995 %T The Influence of Nitrogen Ion Energy on the Quality of GaN Films Grown with Molecular Beam Epitaxy %A T.C. Fu %A Nathan Newman %A Erin C. Jones %A James S. Chan %A Xiaohong Liu %A Michael D. Rubin %A Nathan W. Cheung %A Eicke R. Weber %K Activated nitrogen %K GaN %K molecular beam epitaxy (MBE) %K nitrogen ion energy %X

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.

%B Journal of Electronic Materials %V 24 %P 249-255 %8 04/1995 %G eng %N 4 %1

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%2 LBL-37223 %& 249 %R 10.1007/BF02659683 %0 Journal Article %J Applied Physics Letters %D 1995 %T Thermal Annealing Characteristics of Si and Mg-implanted GaN Thin Films %A James S. Chan %A Nathan W. Cheung %A Lawrence F. Schloss %A Erin C. Jones %A William S. Wong %A Nathan Newman %A Xiaohong Liu %A Eicke R. Weber %A A. Gassman %A Michael D. Rubin %K annealing %K crystal doping %K defect states %K electrical properties %K gallium nitrides %K ion implantation %K magnesium additions %K microstructure %K silicon additions %X

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.

%B Applied Physics Letters %V 68 %P 2702-2704 %8 03/1996 %G eng %N 19 %1

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%2 LBL-37372 %& 2702 %R 10.1063/1.116314 %0 Conference Paper %D 1994 %T Fundamental Materials-Issues Involved in the Growth of GaN by Molecular Beam Epitaxy %A Nathan Newman %A T.C. Fu %A Z. Liu %A Zuzanna Liliental-Weber %A Michael D. Rubin %A James S. Chan %A Erin C. Jones %A Jennifer T. Ross %A Ian M. Tidswell %A Kin Man Yu %A Nathan W. Cheung %A Eicke R. Weber %X

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.

%G eng %L LBL-37296 %2 LBL-37296