Dr. Zuzanna Liliental-Weber Profile

Dr. Zuzanna Liliental-Weber

at Lawrence Berkeley National Lab

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Author

Publications (3)

Proceedings Article | 7 February 2007 Paper

Two-step epitaxial lateral overgrowth of a-plane GaN by MOCVD

Ü. Özgür, A. Baski, H. Morkoç, X. Ni, Z. Liliental-Weber, H. Everitt

Proceedings Volume 6473, 647303 (2007) https://doi.org/10.1117/12.706826

KEYWORDS: Gallium nitride, Epitaxial lateral overgrowth, Metalorganic chemical vapor deposition, Transmission electron microscopy, Luminescence, Atomic force microscopy, Near field scanning optical microscopy, Picosecond phenomena, Scanning electron microscopy, Excitons

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We report on growth and characterization of epitaxial lateral overgrown (ELO) (11₂^-0) a-plane GaN by metalorganic chemical vapor deposition (MOCVD). The ELO samples were grown using a SiO₂ striped mask pattern consisting of 4 &mgr;m wide open windows and 10 &mgr;m or 20 &mgr;m wide SiO₂ stripes. Different growth rates in Ga- and N-wings along with the wing tilt create a major obstacle for achieving a fully coalesced flat surface in ELO-GaN. To address this problem we have employed a two-step growth method that is able to provide a high height to width aspect ratio in the first growth step followed by enhanced lateral growth in the second step by controlling the growth temperature. Depending on the growth conditions, lateral growth rate of the wings with Ga-polarity were from 2 to 5 times larger than that of the N-polarity wings. We investigated the effects of growth parameters on wing tilt, which was observed to be ~0.25° from the Kikuchi lines using large angle convergent beam electron diffraction (LACBED) and accompanied by some twist (0.09°) between the two opposite wings. Transmission electron microscopy (TEM) results showed that the threading dislocation density in the resulting fully coalesced overgrown GaN was reduced from 4.2×10¹⁰ cm^-2 in the window area to 1.0×10⁸ cm^-2 in the wing area, and that the wing areas contained relatively high density of basal stacking faults, 1.2×10⁴ cm^-1. The recombination of carriers/excitons localized at stacking faults was evident in far-field near bandedge photoluminescence (PL) measured at 10 K. Moreover, atomic force microscopy (AFM) measurements revealed two orders of magnitude higher density of surface pits in window than in wing regions, which could be decorating dislocation termination on surface. Time-resolved PL measurements for the a-plane ELO-GaN samples revealed biexponential decays. The recombination times were significantly increased ( &tgr;₁ =80 ps and &tgr;₂ =250 ps) compared to the standard a-plane epitaxial layers (<45 ps), and ratio of the slow decaying component magnitude to the fast decaying one was more than 1.5, showing considerable reduction of nonradiative centers by lateral overgrowth. In addition, room temperature near-field optical microscopy studies revealed the improved optical quality in the wing regions of the overgrown GaN. As revealed from far-field PL, the band edge luminescence at room temperature was more than two orders of magnitude weaker than the yellow luminescence. Therefore, the overall spectrally integrated near field PL was collected, and its intensity was noticeably stronger in the wing areas with both Ga and N polarity. The much weaker emission at the windows and meeting fronts of the two opposite wings were consistent with the observations of high density of dislocations in the window regions and new defects originating at the meeting boundaries from TEM.

Proceedings Article | 3 March 2006 Paper

TEM studies of laterally overgrown GaN layers grown in polar and non-polar directions

Z. Liliental-Weber, R. Davis, D. Zakharov, B. Wagner

Proceedings Volume 6121, 612101 (2006) https://doi.org/10.1117/12.659227

KEYWORDS: Gallium nitride, Transmission electron microscopy, Silicon carbide, Diffraction, Gallium, Point spread functions, Light emitting diodes, Crystals, Photomicroscopy, Polarization

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Proceedings Article | 22 January 1997 Paper

Al-based thermal oxides in vertical cavity surface emitting lasers

Zuzanna Liliental-Weber, Jack Washburn, Constance Chang-Hasnain, Eicke Weber, S. Ruvimov, W. Swider, Gabriel Li, Meng Li

Proceedings Volume 3006, (1997) https://doi.org/10.1117/12.264224

KEYWORDS: Oxides, Vertical cavity surface emitting lasers, Gallium arsenide, Gallium, Arsenic, Interfaces, Aluminum, Transmission electron microscopy, Reflectors, Oxidation

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