UV transparent single‐crystalline bulk AlN substrates

Bickermann, Matthias; Epelbaum, Boris M.; Filip, Octavian; Heimann, Paul; Nagata, S.; Winnacker, A.

doi:10.1002/pssc.200982601

Cited by 70 publications

(68 citation statements)

References 11 publications

(16 reference statements)

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“…Furthermore, AlN is believed to have a high technological potential as a substrate material for short-wavelength emitters, as the high-band-gap material is transparent up to about 200 nm 2,3 and allows for low-strain active regions composed of high-aluminum-content AlGaN. [4][5][6][7] These applications in turn triggered improvements in the growth of high-quality AlN, [8][9][10] only recently allowing us to investigate the fundamental properties of this semiconductor in unpreceded quality.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic absorption and emission of bulk(11¯00)AlN

et al. 2013

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The intrinsic anisotropic optical properties of wurtzite AlN are investigated in absorption and emission. Full access to the anisotropy of the optical response of the hexagonal material is obtained by investigating the (1100) plane of a high-quality bulk crystal allowing electric field E polarization perpendicular (E ⊥ c) and parallel (E c) to the optical axis c. Spectroscopic ellipsometry yields the ordinary (ε ⊥ ) and extraordinary (ε ) dielectric functions (DFs) from 0.58 up to 20 eV. The comparison of the experimental data with recently calculated DFs demonstrates that Coulomb interaction has a strong impact not only on the spectral dependence around the fundamental absorption edge but also on the high-energy features usually discussed in terms of van Hove singularities. The fits of the second-order derivatives of ε and ε ⊥ provide the transition energies for the main features in this range. The DFs close to the fundamental absorption edge, dominated by free excitons, exciton-phonon complexes, and the exciton continuum, are independently confirmed by reflectivity and synchrotron-based photoluminescence excitation studies. Values for the band gaps, the crystal field ( cf = −221 ± 2 meV), and spin-orbit splittings ( so = 13 ± 2 meV) are obtained. Furthermore, we obtain accurate values for the static dielectric constants of ε S⊥ = 7.65 and ε S = 9.21, entering, e.g., the calculations of exciton binding energies. Photoluminescence is used to investigate the emission properties of the same sample.

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Section: Introductionmentioning

confidence: 99%

Anisotropic absorption and emission of bulk(11¯00)AlN

et al. 2013

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“…Although AlN should be transparent down to 210 nm due to its wide bandgap of 6 eV, PVT-AlN substrates have shown wide optical absorption bands below the band gap in the blue and UV ranges. [35,44,45] These absorption bands are attributed to the residual impurities such as silicon, oxygen (mainly from the source materials) and carbon (mainly from the reactor parts such as TaC crucible) and intrinsic point defects, and Al vacancies. The underlying mechanisms for the formation of these bands are still under discussion.…”

Section: Growth and Optical Properties Of Bulk Aln For Duv Ledsmentioning

confidence: 99%

“…The underlying mechanisms for the formation of these bands are still under discussion. [35,39,[44][45][46][47][48][49][50] Specifically, at least three absorption bands at 2.8 eV, 3.3-4.3 eV and 4.7 eV were found and discussed for PVT-grown AlN. The origin of the 2.8 eV band is still an issue of intense debate.…”

Section: Growth and Optical Properties Of Bulk Aln For Duv Ledsmentioning

confidence: 99%

“…[50] However, others attributed to transitions between oxygen on N sites (ON) and VAl (ON-VAl). [44] The broad 3.3-4.3 eV band is presumably associated with VAl and/or oxygen related complexes, and reduction of oxygen contaminations in the source material was found to lead to a significant decrease of UV absorption in both colorless and yellowish areas of bulk AlN. [44] The 4.7 eV band with an absorption coefficient above 1000 cm -1 , which is detrimental to DUV LEDs with emission wavelength shorter than 270 nm, was typically observed in crystals grown with TaC crucibles.…”

Section: Growth and Optical Properties Of Bulk Aln For Duv Ledsmentioning

confidence: 99%

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Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes

Ding¹,

Avrutin²,

Özgür³

et al. 2017

Preprint

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Abstract:We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV) light-emitting diodes (LEDs), with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances in the methods for the growth of bulk single crystal AlN intended as a native substrate together with a discussion of its UV transparency. It should be stated, however, that due to the high-cost of bulk AlN substrates at the time of this writing, the growth of DUV LEDs on foreign substrates such as sapphire still dominates the field. On the deposition front, the heteroepitaxial growth approaches incorporate high-temperature metal organic chemical vapor deposition (MOCVD) and pulsed-flow growth, a variant of MOCVD, with the overarching goal of enhancing adatom surface mobility, and thus epitaxial lateral overgrowth which culminates in minimization the effect of lattice-and thermal-mismatches. This is followed by addressing the benefits of pseudomorphic growth of strained high Al-molar fraction AlGaN on AlN. Finally, methods utilized to enhance both p-and n-type conductivity of high Al-molar fraction AlGaN are reviewed.

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“…The reddish samples turned out to contain Fe 2+ impurity (Ilyin et al, 2010). The below band-gap absorption bands limiting UV transparency are attributed to the point defects (Bickermann et al, 2010), for example, the band-to-impurity absorption manifesting itself as yellow coloration is thought to be related to either the doubly negative charged state V…”

Section: Sublimation Growth Of Aln Crystalsmentioning

confidence: 99%