Growth of AlGaN alloys exhibiting enhanced luminescence efficiency

Sampath, Anand V.; Garrett, Gregory A.; Collins, Charles J.; Sarney, Wendy L.; Readinger, Eric D.; Newman, P. G.; Shen, H.; Wraback, Michael

doi:10.1007/s11664-006-0113-1

Cited by 30 publications

(15 citation statements)

References 14 publications

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“…However, as these samples were all grown on c-plane sapphire with a similar buffer layer, they are all likely to have a similar large dislocation density. Furthermore, characterization of our NCI-AlGaN films by XRD shows no evidence of (0001) reflections [6], forbidden in a random wurtzite alloy but observed in ordered alloys, indicating that ordering is not responsible for the formation of the NCI regions in these films. Rather, these results indicate that nearly stoichiometric growth conditions promote the spontaneous formation of NCI regions in AlGaN alloys grown by PA-MBE.…”

Section: Growth Of Nci-algan Alloysmentioning

confidence: 85%

Suppression of non‐radiative effects in AlGaN through nanometer scale compositional inhomogeneities

Sampath

Garrett

Enck

et al. 2011

Phys. Status Solidi C

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UV light emitting diodes (UVLEDs) emitting at wavelengths shorter than 365 nm remain in the research and development stage, with external quantum efficiencies and device operating lifetimes well below that of commercially available blue LEDs. These limitations are partially attributable to the large density of dislocations in these devices that arise due to heteroepitaxial growth of high AlN mole fraction III‐Nitride semiconductors and act as non‐radiatve recombination centers that reduce efficiency and increase debilitating heating. An approach to mitigating this problem is to incorporate nanometer scale compositional inhomogeneities within the AlGaN (NCI‐AlGaN) active region of a UVLED that can enhance the internal quantum efficiency by concentrating carriers within regions of narrow bandgap surrounded by a wider band gap matrix. In this paper we report on the growth and characterization of NCI‐AlGaN alloys deposited by plasma‐assisted molecular beam epitaxy. Growth under N‐limited and nearly stoichiometric growth conditions promote the spontaneous formation of these NCI regions. This is attributed to lower adatom mobility of group III and N species on the AlGaN layer surface under these conditions as well as the formation of beneficial surface faceting. Optical characterization by both temperature dependent, time‐resolved and time‐integrated photoluminescence demonstrates the capability for NCI regions to suppress non‐radiative recombination in these active regions despite the presence of a large density of defects. However, reduction of the defect density, both dislocations and impurities, improves the performance of these active regions. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Section: Growth Of Nci-algan Alloysmentioning

confidence: 85%

Suppression of non‐radiative effects in AlGaN through nanometer scale compositional inhomogeneities

Sampath

Garrett

Enck

et al. 2011

Phys. Status Solidi C

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“…Such inhomogeneities in the Al x Ga 1Àx N layers with the middle-range Al content (0.25 < x < 0.5), grown by PA MBE, can originate from a considerable difference in surface mobility of Ga and Al adatoms in the middle growth-temperature range (700-750 C). [20][21][22] However, the reduction of the growth temperature below 700 C and maintaining the slightly metal-rich growth conditions, realized for the AlGaN growth in both A and B samples, should yield homogeneous alloys, as it occurred in the case of sample A. Thus, one can conclude that much stronger alloy inhomogeneity in sample B is generally induced by the 3D surface morphology inherited from the AlN buffer layer.…”

Section: The Quantum Confined Stark Effect and Exciton Localizationmentioning

confidence: 94%

Suppression of the quantum-confined Stark effect in AlxGa1−xN/AlyGa1−yN corrugated quantum wells

Торопов

Shevchenko

Shubina

et al. 2013

Journal of Applied Physics

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We report comparative studies of 6-nm-thick Al x Ga 1Àx N/Al y Ga 1Ày N pyroelectric quantum wells (QWs) grown by plasma-assisted molecular beam epitaxy on c-sapphire substrates with a thick AlN buffer deposited under different growth conditions. The Al-rich growth conditions result in a 2D growth mode and formation of a planar QW, whereas the N-rich conditions lead to a 3D growth mode and formation of a QW corrugated on the size scale of 200-300 nm. Time-resolved photoluminescence (PL) measurements reveal a strong quantum-confined Stark effect in the planar QW, manifested by a long PL lifetime and a red shift of the PL line. In the corrugated QW, the emission line emerges 200 meV higher in energy, the low-temperature PL lifetime is 40 times shorter, and the PL intensity is stronger ($4 times at 4.5 K and $60 times at 300 K). The improved emission properties are explained by suppression of the quantum-confined Stark effect due to the reduction of the built-in electric field within the QW planes, which are not normal to the [0001] direction, enhanced carrier localization, and improved efficiency of light extraction. V C 2013 AIP Publishing LLC.[http://dx

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“…The samples grown on bulk AlN substrates consisted of a 600 nm thick, 70% AlN mole fraction, NCI-AlGaN film deposited directly on the substrates by plasma assisted molecular beam epitaxy using conditions published elsewhere [6]. Prior to introduction into the reactor, the N-polar backsides of the substrates were sputter coated with a $2 lm thick Ti film to improve heating uniformity, which was then capped with a protective SiO layer to prevent damage to the film during chemical preparation.…”

Section: Experimental Methodsmentioning

confidence: 99%

Characterization of nanometer scale compositionally inhomogeneous AlGaN active regions on bulk AlN substrates

Sampath

Garrett

Readinger

et al. 2010

Solid-State Electronics

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a b s t r a c tThe optical and structural properties of AlGaN active regions containing nanoscale compositional inhomogeneities (NCI) grown on low dislocation density bulk AlN substrates are reported. These substrates are found to improve the internal quantum efficiency and structural quality of NCI-AlGaN active regions for high Al content alloys, as well as the interfaces of the NCI with the surrounding wider bandgap matrix, as manifested in the absence of any significant long decay component of the low temperature radiative lifetime, which is well characterized by a single exponential photoluminescence decay with a 330 ps time constant. However, room temperature results indicate that non-radiative recombination associated with the high point defect density becomes a limiting factor in these films even at low dislocation densities for larger AlN mole fractions.Published by Elsevier Ltd.

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Growth of AlGaN alloys exhibiting enhanced luminescence efficiency

Cited by 30 publications

References 14 publications

Suppression of non‐radiative effects in AlGaN through nanometer scale compositional inhomogeneities

Suppression of non‐radiative effects in AlGaN through nanometer scale compositional inhomogeneities

Suppression of the quantum-confined Stark effect in AlxGa1−xN/AlyGa1−yN corrugated quantum wells

Characterization of nanometer scale compositionally inhomogeneous AlGaN active regions on bulk AlN substrates

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