Recrystallization of epitaxial GaN under indentation

Dhara, Sandip; Das, C. R.; Hsu, Hsu Cheng; Raj, Baldev; Bhaduri, A.K.; Chen, L. C.; Chen, K. H.; Albert, S. K.; Ray, Ayan

doi:10.1063/1.2907851

Cited by 14 publications

(16 citation statements)

References 16 publications

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“…A 1 (TO) be the starting of A 1 symmetry phonon modes and this frequency corresponds to the quasi-confined modes in isolated nanowire model which are the continuation of SO modes for frequencies below A 1 (TO). TO modes will appear when the orientations have different crystalline planes [28]. TO vibration modes are exhibited when the q vector (propagation direction) travels in between the c-and a-planes.…”

Section: Optical Propertiesmentioning

confidence: 99%

HVPE growth of self-aligned GaN nanorods on c-plane, a-plane, r-plane, and m-plane sapphire wafers

et al. 2015

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Herein, we report the self-aligned growth of GaN nanorods on different orientations of sapphire like c-, a-, rand m-plane substrates by hydride vapor phase epitaxy. Vertical c-axis orientation of GaN NRs is obtained on c-plane [0001] and a-plane 11 20 ½ sapphire and a skew or inclined NRs on r-plane, and inclined intertwined but self-aligned NR array was formed on m-plane sapphire. GaN (002) and (004) peaks were obtained on c-and a-plane sapphire, whereas (110), (103), and (103) only were observed on r-and mplanes, respectively. In the case of r-and m-plane-grown GaN, A 1 transverse optical mode is dominant, and the A 1 longitudinal optical mode is suppressed. Conversely, in the case of c-and a-plane, it is reversed. The probable reason is the optical mode vibrations difference along the differently inclined NRs surfaces. In addition, the specimen exhibits surface optical modes too. The optical behavior of GaN NR on m-sapphire shows an intensity variation when measured in different angular rotations of the specimen by photoluminescence which is because of the higher area of excitation in the case of axial surfaces and lower area of excitation in radial surface. Their epitaxial crystallographic relationship with the substrates and the reasons for the self-aligned orientations are discussed. The anomalies found in the optical behavior are attributed to Raman antenna effect and so on. The self-aligned intertwined GaN NRs find suitable applications in polarizer.

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Section: Optical Propertiesmentioning

confidence: 99%

HVPE growth of self-aligned GaN nanorods on c-plane, a-plane, r-plane, and m-plane sapphire wafers

et al. 2015

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“…These high stresses are reported for pressure-induced phase transformations to denser crystalline (c-) and amorphous forms in monovalently [1 -3] and covalently bonded compound [4,5] semiconductors along with plastic deformation, leading to recrystallization by dislocation activity in ionic-bonded compound semiconductors. [6] Study of materials under pressure is always of immense interest both for electronic and mechanical properties. In addition, the study of transformation to the high-pressure phase has technological importance for having control in the precision micromachining process steps using enhancement of ductility in these systems.…”

Section: Introductionmentioning

confidence: 99%

A complete Raman mapping of phase transitions in Si under indentation

Das

Hsu

Dhara

et al. 2009

J Raman Spectroscopy

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Crystalline Si substrates are studied for pressure-induced phase transformation under indentation at room temperature (RT) using a Berkovich tip. Raman spectroscopy, as a nondestructive tool, is used for the identification of the transformed phases. Raman lines as well as area mapping are used for locating the phases in the indented region. Calculation of pressure contours in the indented region is used for understanding the phase distribution. We report here a comprehensive study of all the phases of Si, reported so far, leading to possible understanding of material properties useful for possible electromechanical applications. As a major finding, distribution of the amorphous phase in the indented region deviates from the conventional wisdom of being in the central region alone. We present phase mapping results for both Si(100) and Si(111) substrates.

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“…The mechanism responsible for the 'pop-in' bursts appears to be associated with the nucleation and movement of dislocation sources. [14,15] A hardness value of ∼10 GPa is achieved in our indentation study, [2] and the value is comparable to the bulk value of GaN. [16] It is also observed that the hardness of the GaN film is also sensitive to the loading rate (strain rate), as shown in Fig 3(a).…”

Section: Nucleation and Dynamics Of Defects Under Indentation Stress mentioning

confidence: 54%

“…A detailed description of compliance curve along with 'pop-in' bursts in the loading line is reported in our earlier studies, [2] and also shown in Fig. S1 (Supporting Information) for high and low loads.…”

Section: Nucleation and Dynamics Of Defects Under Indentation Stress mentioning

confidence: 99%

“…Several techniques have been adopted for the diminution of dislocation densities in GaN, [1] including our recent report on recrystallization under indentation. [2] A layer-bylayer defect formation in GaN is studied using structural studies, [3] without a detailed atomistic model of its origin and dynamics. It necessitates a detailed study of the lattice dynamics in the stressfree region, as well as in the strained volume for comparison.…”

Section: Introductionmentioning

confidence: 99%

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The mechanism of the recrystallization process in epitaxial GaN under dynamic stress field: atomistic origin of planar defect formation

Das

Dhara

Hsu

et al. 2009

J Raman Spectroscopy

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The mechanism of the recrystallization in epitaxial (0001) GaN film, introduced by the indentation technique, is probed by lattice dynamic studies using Raman spectroscopy. The recrystallized region is identified by micro‐Raman area mapping. ‘Pop‐in’ bursts in loading lines indicate nucleation of dislocations and climb of dislocations. These processes set in plastic motion of lattice atoms under stress field at the center of indentation for the initiation of the recrystallization process. A planar defect migration mechanism is evolved. A pivotal role of vacancy migration is noted, for the first time, as the rate‐limiting factor for the dislocation dynamics initiating the recrystallization process in GaN. Copyright © 2009 John Wiley & Sons, Ltd.

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Recrystallization of epitaxial GaN under indentation

Cited by 14 publications

References 16 publications

HVPE growth of self-aligned GaN nanorods on c-plane, a-plane, r-plane, and m-plane sapphire wafers

HVPE growth of self-aligned GaN nanorods on c-plane, a-plane, r-plane, and m-plane sapphire wafers

A complete Raman mapping of phase transitions in Si under indentation

The mechanism of the recrystallization process in epitaxial GaN under dynamic stress field: atomistic origin of planar defect formation

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