On the origin of the 265 nm absorption band in AlN bulk crystals

Collazo, Ramón; Xie, Jinqiao; Gaddy, Benjamin E.; Bryan, Zachary; Kirste, Ronny; Hoffmann, Marc P.; Dalmau, Rafael; Moody, Baxter; Kumagai, Yoshinao; Nagashima, Toru; Kubota, Yuki; Kinoshita, Toru; Koukitu, Akinori; Irving, Douglas L.; Sitar, Zlatko

doi:10.1063/1.4717623

Cited by 149 publications

(153 citation statements)

References 28 publications

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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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“…21 In addition, Bryan et al have shown that an unoptimized growth condition of the AlGaN DUV MQW on the AlN substrate can lower the IQE significantly. 22 Moreover, Collazo et al have shown that bulk AlN substrate can have a high absorption coefficient of a > 350 cm À1 in the DUV range because of carbon impurities 23 and Xie et al show that there was considerable light leakage towards the substrate for the lowthreshold photo-pumped DUV MQW laser grown on the AlN substrate because of imperfect optical confinement. 14 Thus, the severe absorption could limit the performance of AlGaN DUV MQW laser grown on currently available AlN substrates.…”

mentioning

confidence: 99%

Low-threshold stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates

Detchprohm

Kao

et al. 2014

Applied Physics Letters

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Optically pumped deep-ultraviolet (DUV) lasing with low threshold was demonstrated from AlGaN-based multiple-quantum-well (MQW) heterostructures grown on sapphire substrates. The epitaxial layers were grown pseudomorphically by metalorganic chemical vapor deposition on (0001) sapphire substrates. Stimulated emission was observed at wavelengths of 256 nm and 249 nm with thresholds of 61 kW/cm2 and 95 kW/cm2 at room temperature, respectively. The thresholds are comparable to the reported state-of-the-art AlGaN-based MQW DUV lasers grown on bulk AlN substrates emitting at 266 nm. These low thresholds are attributed to the optimization of active region and waveguide layer as well as the use of high-quality AlN/sapphire templates. The stimulated emission above threshold was dominated by transverse-electric polarization. This work demonstrates the potential candidacy of sapphire substrates for DUV diode lasers.

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“…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%

“…[3] The origin of 4.7 eV band was reportedly related to the carbon contaminations. [48] Density functional theory (DFT) calculations have predicted that substitutional carbon on the nitrogen site (CN) introduces absorption at this energy. Optical absorption measurements performed on a series of single crystalline AlN wafers with different carbon concentrations showed that the absorption coefficient at 4.7 eV linearly increased with carbon content, supporting the prediction of CN being responsible for the said absorption.…”

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

confidence: 99%

“…Optical absorption measurements performed on a series of single crystalline AlN wafers with different carbon concentrations showed that the absorption coefficient at 4.7 eV linearly increased with carbon content, supporting the prediction of CN being responsible for the said absorption. [48] Another promising method for growing bulk AlN crystals is hydride vapor phase epitaxy (HVPE). Compared to the PVT produced AlN, HVPE grown AlN has much better transparency in the DUV range due to better controlled carbon incorporation.…”

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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On the origin of the 265 nm absorption band in AlN bulk crystals

Cited by 149 publications

References 28 publications

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

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

Low-threshold stimulated emission at 249 nm and 256 nm from AlGaN-based multiple-quantum-well lasers grown on sapphire substrates

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

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