Optically pumped UV lasers grown on bulk AlN substrates

Wunderer, Thomas; Chua, C.L.; Northrup, John E.; Yang, Zhihong; Johnson, N. M.; Kneissl, Michael; Garrett, Gregory A.; Shen, Huihui; Wraback, Michael; Moody, Baxter; Craft, H. S.; Schlesser, R.; Dalmau, Rafael; Sitar, Zlatko

doi:10.1002/pssc.201100424

Cited by 72 publications

(45 citation statements)

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“…[1][2][3][4][5][6][7][8][9][10] The demand on UV light emission, mainly for water purification purposes, 11 pushes the research on light emitting diodes (LEDs) and laser diodes (LDs) operating at short wavelengths around 270 nm. In contrast to generic LEDs, where light is emitted perpendicular to the substrate, LDs typically are edge emitters due to the cavity produced by cleaving perpendicular to the surface and quantum well plane.…”

Section: Introductionmentioning

confidence: 99%

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Neuschl

Helbing

Knab

et al. 2014

Journal of Applied Physics

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Extremely weak surface emission from (0001) c -plane AlGaN multiple quantum well structure in deep-ultraviolet spectral region Valence-band splitting and band-gap reduction in ordered GaInAs/InPThe valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k Á p theory yields a critical relative aluminum concentration x c ¼ ð0:0960:05Þ for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with C 9 symmetry of b C 9 ¼ 0:85eV, and propose a possible bowing for the crystal field energy of b cf ¼ À0:12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al x Ga 1Àx N=Al y Ga 1Ày N quantum well structures is discussed for different compositions. V C 2014 AIP Publishing LLC. [http://dx.

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Section: Introductionmentioning

confidence: 99%

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Neuschl

Helbing

Knab

et al. 2014

Journal of Applied Physics

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“…6 One approach is to deposit the diode layer, with high Al content, directly on an AlN single crystal. This kind of substrate is promising for an improvement of the crystal quality, 7,8 and recently, well operating LEDs 9 and lasers 10,11 have been presented. Nevertheless, many fundamental properties such as the exact electronic structure for typical dopants are not known.…”

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confidence: 99%

Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Neuschl

Thonke

Feneberg

et al. 2013

Applied Physics Letters

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We report on the identification of a two-electron transition for the shallow donor silicon in homoepitaxial aluminum nitride (AlN). One c-oriented sample was analyzed by low temperature photoluminescence spectroscopy on multiple excitation spots. We find a unique correlation of one single emission band, 76.6 meV below the free excitonic emission, with the luminescence of excitons bound to neutral silicon proving the identity as a two-electron transition. The assignment is confirmed by temperature dependent photoluminescence investigations. We find a donor ionization energy of ð63:5 6 1:5Þ meV for silicon in AlN. V C 2013 AIP Publishing LLC.Recent interest in light emitting devices operating in the deep UV spectral region 1 is due to promising applications such as the deactivation of microorganisms by exposure to light with short wavelengths. Several research groups are working on light emitting diodes (LEDs) based on aluminum gallium nitride (AlGaN) fabricated on foreign substrates such as sapphire 2-4 or silicon carbide. 5 As a consequence, these structures suffer from high defect densities due to the lattice and thermal expansion coefficient mismatch between the substrate material and the epitaxial film, directly degrading the efficiency of the device. 6 One approach is to deposit the diode layer, with high Al content, directly on an AlN single crystal. This kind of substrate is promising for an improvement of the crystal quality, 7,8 and recently, well operating LEDs 9 and lasers 10,11 have been presented. Nevertheless, many fundamental properties such as the exact electronic structure for typical dopants are not known. Only recently, homoepitaxial AlN layers of good crystal quality became available allowing the proper identification of single bound excitonic emission bands. 12,13 However, for the mostly present donor silicon (Si), there is no agreement on the ionization energy. There is an ongoing discussion, whether Si Al undergoes a strong lattice relaxation and forms a deep DX center, where the dopant atom captures a second electron. Several theoretical studies predict DX center formation for Si Al , 14,15 whereas others find silicon to be a shallow donor in wurtzite AlN. 16,17 Experimentally, the majority of studies shows n-type conductivity after silicon doping, 18-24 although they find very different values for the ionization energy ranging from 86 to 570 meV. On the other hand, there are two detailed reports about DX center formation found by spectrally resolved photoconductivity and electron paramagnetic resonance. 25,26 In this letter, we present a detailed investigation of a homoepitaxially grown wurtzite AlN layer by means of temperature dependent photoluminescence (PL) spectroscopy. Exposure at multiple excitation spots and the temperature dependent behavior of the emission bands observed allow for an identification of a two-electron transition with shallow silicon donors involved. We further discuss the presented results in the framework of possible DX center formation.The sample under investigat...

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“…Highly conductive n-Al x Ga 12x N layers with aluminum mole fractions above 80% Frank Mehnke, 1,a) Tim Wernicke, 1 Harald Pingel, 1 Christian Kuhn, 1 Christoph Reich, 1 Viola Kueller, 2 Arne Knauer, 2 Mickael Lapeyrade, 2 Markus Weyers, 2 Silicon doping of Al x Ga 1Àx N layers with high aluminum mole fractions (0.8 < x < 1) was studied. The AlGaN:Si layers were pseudomorphically grown by metalorganic vapor phase epitaxy on low defect density epitaxially laterally overgrown AlN/sapphire templates.…”

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confidence: 99%

Highly conductive n-AlxGa1−xN layers with aluminum mole fractions above 80%

Mehnke

Wernicke

Pingel

et al. 2013

Applied Physics Letters

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Silicon doping of AlxGa1−xN layers with high aluminum mole fractions (0.8 < x < 1) was studied. The AlGaN:Si layers were pseudomorphically grown by metalorganic vapor phase epitaxy on low defect density epitaxially laterally overgrown AlN/sapphire templates. The effects of SiH4/III ratio and aluminum content on the resistivity, the carrier concentration, and the mobility have been investigated. By variation of the SiH4/III ratio during the growth of AlxGa1−xN:Si layers, a recorded low resistivity of Al0.81Ga0.19N:Si was obtained with 0.026 Ω cm. The resistivity increases exponentially with increasing aluminum content to 3.35 Ω cm for Al0.96Ga0.04N, and the optimum SiH4/III ratio is shifted towards lower values. Hall effect measurements show that the increase of the resistivity with increasing aluminum mole fraction is mainly caused by a decrease of the carrier density. The optimized Al0.81Ga0.19N:Si exhibits a carrier concentration of 1.5 × 1019 cm−3 and a mobility of the carriers of 16.5 cm2 V−1 s−1.

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Optically pumped UV lasers grown on bulk AlN substrates

Cited by 72 publications

References 0 publications

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Composition dependent valence band order in c-oriented wurtzite AlGaN layers

Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Highly conductive n-AlxGa1−xN layers with aluminum mole fractions above 80%

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