Influence of substrate-induced biaxial compressive stress on the optical properties of thin GaN films

Rieger, W.; Metzger, T. H.; Angerer, H.; Dimitrov, R.; Ambacher, O.; Stutzmann, M.

doi:10.1063/1.116115

Cited by 223 publications

(84 citation statements)

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“…The biaxial stress σ in the samples, due to mismatch of the lattice constants and the thermal [ ] p , expansion coefficients of the substrate and epitaxial films, was calculated from the results of HRXRD-measurements and is estimated to be below 0.4 GPa. Therefore, an upper limit of 10 meV for the stress-induced shift of the bandgap can be calculated using dE g /dσ ≈ 25 meV/GPa [18]. As a consequence, an upper limit of the bandgap shift towards higher energies caused by biaxial compressive stress should be approximately 10 meV at room temperature.…”

Section: Dependence Of the Absorption Edge On The Al Molar Fractionmentioning

confidence: 99%

AlGaN-Based Bragg Reflectors

Ambacher

Arzberger

Brunner

et al. 1997

MRS Internet j. nitride semicond. res.

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We have studied the dependence of the absorption edge and the refractive index of wurtzite Al x Ga 1-x N films on composition using transmission, ellipsometry and photothermal deflection spectroscopy. The Al molar fraction of the Al x Ga 1-x N films grown by plasma-induced molecular beam epitaxy was varied through the entire range of composition (0 ≤ x ≤ 1). We determined the absorption edges of Al x Ga 1-x N films and a bowing parameter of 1.3 ± 0.2 eV. The refractive index below the bandgap was deduced from the interference fringes, the dielectric function between 2.5 and 25 eV from ellipsometry measurements. The measured absorption coefficients and refractive indices were used to calculate the design and reflectivity of AlGaN-based Bragg reflectors working in the blue and near-ultraviolet spectral region.

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Section: Dependence Of the Absorption Edge On The Al Molar Fractionmentioning

confidence: 99%

AlGaN-Based Bragg Reflectors

Ambacher

Arzberger

Brunner

et al. 1997

MRS Internet j. nitride semicond. res.

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“…The NBE peak position for S2 was same as S3, however for S1 the NBE position is found to be at 361.65 nm. Generally, the PL band e edge peak position will shift towards higher wavelength (in comparison to the unstressed bulk GaN film at~364.4 nm) as the compressive stress relaxation occurs in GaN film [29]. Thus, the shift witnessed in PL peak position of grown GaN samples with increasing plasma power infers relaxation of stress in the MBE grown films.…”

Section: Resultsmentioning

confidence: 99%

Influence of active nitrogen species on surface and optical properties of epitaxial GaN films

Aggarwal

Krishna

Mishra

et al. 2016

Journal of Alloys and Compounds

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a b s t r a c tInfluence of active nitrogen species on surface and optical properties of homoepitaxial GaN films grown on GaN epilayers has been investigated. The epitaxial GaN films were grown at varying plasma powers (350e500 W) under identical growth conditions. High resolution X-Ray diffraction, Field Emission Scanning Electron Microscopy, Atomic Force Microscopy and Photoluminescence measurements were employed to characterize the structural, morphological and optical properties of the grown GaN films. High plasma power (500 W) lead to an increment in active nitrogen radicals and yielded high crystalline quality with reduced dislocations compared to low plasma power (350, 400 W) which divulge the presence of metallic gallium on the surface and low roughness. The valence band maximum position, electron affinity and ionization energy of the films increased with increment in plasma power. PL measurements revealed narrow and intense band to band edge emission with negligible defect related yellow band peak for the sample grown at 500 W. The analysis conveyed that higher amount of active nitrogen species encouraged good optical properties with insignificant defect states which can be employed for the fabrication of high performance optoelectronic & photovoltaic devices.

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“…Rieger et al 59 reported shifts in the photoluminescence caused by substrate-induced biaxial compressive stress: dE PL =dr ¼ 27 6 4 meV=GPa. 59 If an extrapolation of this value is used as a reference for the variation in the band gap in the tensile range, a decrease as high as 240 meV could be expected in the deposition at 1000 C, corresponding to the estimated tension of $ 9 GPa.…”

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%

“…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%

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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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Influence of substrate-induced biaxial compressive stress on the optical properties of thin GaN films

Cited by 223 publications

References 0 publications

AlGaN-Based Bragg Reflectors

AlGaN-Based Bragg Reflectors

Influence of active nitrogen species on surface and optical properties of epitaxial GaN films

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

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