PVT growth of bulk AlN crystals with low oxygen contamination

Bickermann, Matthias; Epelbaum, Boris M.; Winnacker, A.

doi:10.1002/pssc.200303280

Cited by 36 publications

(31 citation statements)

References 15 publications

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“…Figure 1 compares the low temperature ͑10 K͒ PL spectra of AlN homoepilayers with three different orientations ͑a-plane, c-plane and m-plane͒ ͑a͒ in a broad spectral range from 2.0 to 6.2 eV and ͑b͒ in a narrower spectral range from 5.8 to 6.2 eV. We observed weak and deep impurity related emission bands centered around 2.9 eV and 4.4 eV from the m-plane sample related to O impurities 15 and at 4.70 eV in a-plane sample related to Al vacancy complex with one negative charge, 16 ͑V Al -complex͒ 1− . However, the intensities of these impurity transitions are less than 1% of the corresponding band-edge emissions, which confirms the high optical quality of our AlN homoepilayers.…”

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confidence: 82%

Photoluminescence properties of AlN homoepilayers with different orientations

Sedhain

Nepal

Nakarmi

et al. 2008

Applied Physics Letters

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AlN homoepilayers and heteroepilayers were grown on polar c-plane and nonpolar a-plane and m-plane orientations of AlN bulk and sapphire substrates by metal organic chemical vapor deposition. A systematic comparative study of photoluminescence properties of these samples revealed that all AlN homoepilayers ͑c, a and m planes͒ were strain free with an identical band gap of about 6.099 ͑6.035͒ eV at 10 ͑300͒ K, which is about 42 meV below the band gap of c-plane AlN heteroepilayers grown on sapphire. Also, nonpolar a-plane homoepilayers have the highest emission intensity over all other types of epilayers. We believe that a-plane AlN homoepilayers have the potential to provide orders of magnitude improvement in the performance of new generation deep UV photonic devices. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2965613͔ AlN has a complete solid solubility with GaN ͑Ref. 1͒ and emerged as an important semiconductor material for applications of light emitters down to 200 nm ͑Ref. 2͒ and detectors in the deep ultraviolet ͑DUV͒ and extreme UV spectral region. 3,4 Quantum wells ͑QWs͒ have been the device structure of choice for efficient III-nitride semiconductor based light emitters. 5,6 Conventional nitride c-plane multiple QW structures generate fixed sheet charges at the interfaces due to the spontaneous and piezoelectric polarization. 7-10 which induce internal electric fields, lead to carrier separation, and reduce the radiative recombination rate. Consequently, optoelectronic devices such as light emitting diodes and laser diodes based on heteroepitaxial c-plane oriented III-nitride materials possess reduced internal quantum efficiencies.There has been tremendous effort in the investigation of nonpolar a-plane and m-plane III-nitride epilayers 11 and optoelectronic devices with QW structures 9,10 to reduce the effects of internal electric fields. To achieve QW and other heterostructure based devices with improved performance, optical properties of epilayers grown on different orientations of available substrates have to be better understood. Furthermore, most previous studies on the fundamental band structures of AlN have been carried out for heteroepilayers grown on sapphires, which are plagued by lattice mismatch induced strain and high threading dislocation density, which significantly inhibited our ability for precisely determining the fundamental band structure parameters of AlN. In this work, we report a systematic comparative study of optical properties of both homoepitaxial and heteroepitaxial layers of AlN grown on polar c-plane as well as a-plane and m-plane orientations probed by DUV photoluminescence ͑PL͒.AlN bulk single crystal substrates were produced by sublimation crystal growth using polycrystalline AlN wafer as seeds and have a thickness of about 1 mm and an average grain size of about 2 ϫ 3 mm 2 . 12 The surface of AlN bulk crystal substrates was prepared by chemical mechanical polishing ͑done by NovaSiC͒ that provided a surface roughness of about 1 -4 nm. The dislocation density i...

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confidence: 82%

Photoluminescence properties of AlN homoepilayers with different orientations

Sedhain

Nepal

Nakarmi

et al. 2008

Applied Physics Letters

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“…The optical appearance of such samples is determined by the fact that about half of the grains are yellow and translucent, while the others are brown to non-transparent. Additionally, most grain boundaries also appear dark and nontransparent [5,6]. Microscopy studies confirm that the dark and opaque crystallites and grain boundaries of samples grown at high temperatures suffer from void formation.…”

Section: Resultsmentioning

confidence: 82%

“…Besides availability, high structural quality of AlN crystals is considered a prerequisite for substrate use. We succeeded in growing bulk AlN by physical vapor transport (PVT) [5], but the resulting polycrystalline boules were inhomogeneous in respect to optical appearance of different grains as well as grain boundary decoration [6]. In this study, we investigate structural properties of different AlN specimens grown by PVT (freestanding single crystals vs. bulky material) in order to understand nature and origin of these inhomogeneities.…”

Section: Introductionmentioning

confidence: 98%

Structural properties of AlN crystals grown by physical vapor transport

Bickermann

Epelbaum

Winnacker

2005

phys. stat. sol. (c)

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Structural properties of different AlN material grown by physical vapor transport (freestanding single crystals vs. bulky material) are compared. In polycrystalline samples, void formation leading to dark and opaque crystallites and grain boundaries is restricted to high growth temperatures and to grains grown with N-polarity. Single-crystalline freestanding AlN exhibits a zonal structure as growth takes place on multiple faces simultaneously. As a conclusion, optical transmission of different grains varies regardless of void formation: Grains grown with N-polarity appear darker and more opaque than grains grown in other directions. Presumably, impurity incorporation and/or intrinsic defect formation depends on the crystallographic orientation of the facet where growth occurs.

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“…The absorption edge calculated from extrapolation of the linear region of the absorption spectrum was around 6.05 eV. In addition, around 4.5 and 4.8 eV pertinent absorption for oxygen (O) impurity, as reported by several groups [10][11][12], was not observed. Therefore, it was suggested that the residual concentration of O in the AlN layer was low.…”

Section: Article In Pressmentioning

confidence: 78%