The role of high-temperature island coalescence in the development of stresses in GaN films

Böttcher, T.; Einfeldt, S.; Figge, S.; Chierchia, Rosa; Heinke, H.; Hommel, D.; Speck, James S.

doi:10.1063/1.1359780

Cited by 199 publications

(124 citation statements)

References 17 publications

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“…The residual strain on the Al 0.62 Ga 0.38 N buffer layers was caused by strains associated with the growth process, i.e., the lattice mismatch of 13.4% between the buffer and the sapphire, and the compressive thermal mismatch strain that developed while cooling to room temperature. 9 The lattice mismatch between the Al 0.62 Ga 0.38 N buffer layer and sapphire was relaxed by 98%. This extent of relaxation corresponds to a residual strain of approximately −0.27% ͑i.e., compressive͒ in the Al 0.62 Ga 0.38 N. The strain in the Al 0.62 Ga 0.38 N layer due to thermal-expansion mismatch with the sapphire is estimated to be ϳ−0.30%.…”

Section: Resultsmentioning

confidence: 99%

Role of inclined threading dislocations in stress relaxation in mismatched layers

Cantu

Waltereit

et al. 2005

Journal of Applied Physics

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͑0001͒-oriented epitaxial wurtzite III-nitride layers grown on mismatched substrates have no resolved shear stress on the natural basal and prismatic slip planes; however, strained III-nitride layers may gradually relax. We report on the stress relaxation of Al 0.49 Ga 0.51 N layers grown on nominally relaxed Al 0.62 Ga 0.38 N buffer layers on sapphire. The reduction in elastic strain of the Al 0.49 Ga 0.51 N was enhanced by Si doping which caused an increased surface roughness. Despite the Si doping, the films always sustained step-flow growth. The extent of relaxation of the Al 0.49 Ga 0.51 N layer was determined by on-axis -2 scans of ͑000l͒ peaks and reciprocal space maps of inclined ͑off-axis͒ peaks. Cross-section and plan-view transmission electron microscopy studies showed that the threading dislocations in the Al 0.49 Ga 0.51 N layer inclined from the ͓0001͔ direction towards ͗1100͘ directions by ϳ15-25°, perpendicular to their Burgers vector ͑ 1 3 ͗1120͘ ͒ . These inclined threading dislocations have a misfit dislocation component and thus provide stress relief. The contribution of the dislocation inclination to the degree of relaxation has been formulated and the energy release has been determined for dislocation inclination in mismatched stressed layers.

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Section: Resultsmentioning

confidence: 99%

Role of inclined threading dislocations in stress relaxation in mismatched layers

Cantu

Waltereit

et al. 2005

Journal of Applied Physics

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“…3). Actually, HVPE-grown material as investigated here is well known to be under significant tensile strain [24,25], and we therefore tentatively assign the stabilization of the four-core struc- ture as a consequence of significant tensile strain in the sample. Furthermore, the effect of Ga and N vacancies on the stability of the dislocation core has been considered.…”

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confidence: 93%

Strain Induced Deep Electronic States around Threading Dislocations in GaN

et al. 2004

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Combining through-focus high-resolution transmission electron microscopy and hierarchical multiscale simulations consisting of density-functional theory, analytical empirical potentials, and continuum elastic theory we demonstrate the existence of a new dislocation type in GaN. In contrast with all previously identified or suggested dislocation structures in GaN, all core atoms are fully coordinated; i.e., no broken bonds occur, implying that the dislocation should be electrically inactive. However, as we show, the giant local strain-field around the dislocation core, in combination with the small lattice constant of GaN, causes deep defect states and thus electrically active edge dislocations independent on the specific core structure.

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“…Differently, in epitaxial GaN, compressive stress generally dominates, because of the larger thermal expansion coefficient of sapphire. 51,[56][57][58][59][60] Large compressive stresses were also reported in films deposited by RF sputtering for substrate temperatures below 500 C. 25 Both the previous literature 39-41,51,52,56,61 and our analysis of the data in the present study indicate that the observed lattice swelling (with changes in both a and c parameters of the GaN hexagonal cell) can be attributed to three main factors: (i) the coalescence/merging of the crystallites/interfaces; 56 (ii) the loss of film material during and after growth; and (iii) impingement of energetic N and the corresponding creation of selfinterstitials. 34,41,52,62,63 These points are discussed in more detail in the following.…”

Section: Discussionmentioning

confidence: 99%

“…The observed effects largely overcame the compressive stress resulting from the smaller expansion coefficient of GaN in relation to the sapphire substrate, which has been generally observed on epitaxially grown samples. 56,59,60 In the low temperature range (T s < 500 C), the thicker layers are expected to decrease the "memory" effect of the film-substrate interface, helped by the wider grain boundaries and amorphous regions present.…”

Section: Discussionmentioning

confidence: 99%

Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

Schiaber

Leite

Bortoleto

et al. 2013

Journal of Applied Physics

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Growth stresses and cracking in GaN films on (111) The combined effects of substrate temperature, substrate orientation, and energetic particle impingement on the structure of GaN films grown by reactive radio-frequency magnetron sputtering are investigated. Monte-Carlo based simulations are employed to analyze the energies of the species generated in the plasma and colliding with the growing surface. Polycrystalline films grown at temperatures ranging from 500 to 1000 C clearly showed a dependence of orientation texture and surface morphology on substrate orientation (c-and a-plane sapphire) in which the (0001) GaN planes were parallel to the substrate surface. A large increase in interplanar spacing associated with the increase in both a-and c-parameters of the hexagonal lattice and a redshift of the optical bandgap were observed at substrate temperatures higher than 600 C. The results showed that the tensile stresses produced during the film's growth in high-temperature deposition ranges were much larger than the expected compressive stresses caused by the difference in the thermal expansion coefficients of the film and substrate in the cool-down process after the film growth. The best films were deposited at 500 C, 30 W and 600 C, 45 W, which corresponds to conditions where the out diffusion from the film is low. Under these conditions the benefits of the temperature increase because of the decrease in defect density are greater than the problems caused by the strongly strained lattice that occurr at higher temperatures. The results are useful to the analysis of the growth conditions of GaN films by reactive sputtering. V C 2013 AIP Publishing LLC.

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The role of high-temperature island coalescence in the development of stresses in GaN films

Cited by 199 publications

References 17 publications

Role of inclined threading dislocations in stress relaxation in mismatched layers

Role of inclined threading dislocations in stress relaxation in mismatched layers

Strain Induced Deep Electronic States around Threading Dislocations in GaN

Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

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