Status and Prospects of AlN Templates on Sapphire for Ultraviolet Light‐Emitting Diodes

Hagedorn, Sylvia; Walde, Sebastian; Knauer, A.; Susilo, Norman; Pacak, Daniel; Cancellara, Leonardo; Netzel, Carsten; Mogilatenko, A.; Hartmann, C.; Wernicke, Tim; Kneissl, Michael; Weyers, M.

doi:10.1002/pssa.201901022

Cited by 41 publications

(44 citation statements)

References 64 publications

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“…As recently addressed in a review article about substrates for UV LEDs, our group investigates whether HTA can promote dislocation movement and annihilation in Al x Ga 1− x N layers, similar to the TDD reduction in MOVPE‐grown AlN. [ 14 ] To our knowledge, there are no other publications to date that investigate AlGaN annealing at temperatures of up to 1700 °C. Therefore, in this article, a detailed study of the influence of annealing temperature on the properties of Al 0.77 Ga 0.23 N is presented.…”

Section: Introductionmentioning

confidence: 99%

High‐Temperature Annealing of AlGaN

Hagedorn

Khan

Netzel

et al. 2020

Physica Status Solidi (a)

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In the past few years, high‐temperature annealing of AlN has become a proven method for providing AlN layers with low dislocation densities. Herein, the example of Al0.77Ga0.23N is used to investigate whether annealing can also improve the material quality of the ternary alloy. A detailed analysis of the influence of annealing temperature on structural and optical material properties is presented. It is found that with increasing annealing temperature, the threading dislocation density can be lowered from an initial value of 6.0 × 109 down to 2.6 × 109 cm−2. Ga depletion at the AlGaN surface and Ga diffusion into the AlN buffer layer are observed. After annealing, the defect luminescence between 3 and 4 eV is increased, accompanied by an increase in the oxygen concentration by about two orders of magnitude. Furthermore, due to annealing optical absorption at 325 nm (3.8 eV) occurs, which increases with increasing annealing temperature. It is assumed that the reason for this decrease in ultraviolet (UV) transmittance is the increasing number of vacancies caused by the removal of group‐III and N atoms from the AlGaN lattice during annealing.

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Section: Introductionmentioning

confidence: 99%

High‐Temperature Annealing of AlGaN

Hagedorn

Khan

Netzel

et al. 2020

Physica Status Solidi (a)

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“…Consequently, a high annealing temperature is not absolutely necessary to reach the low TDD. This experiment also shows that for an annealing temperature of 1730 C the TDD cannot be further decreased by increasing the annealing duration from 1 to 3 h. In addition, the sample annealed at 1730 C for 3 h exhibits an increased surface roughness in the edge region (inset of Figure 6b) with up to 50 nm high steps [20] Copyright 2020, Wiley-VCH. show that the interface between AlN and sapphire is strongly rounded and irregular in the edge region.…”

Section: Annealing Temperature and Annealing Duration Impact On Aln Elo Templatesmentioning

confidence: 72%

“…b) TDD DSE plotted against annealing temperature (T HTA ) with dashed line indicating TDD DSE for the sample without HTA. Inset in (b) shows a Nomarski light microscopy image indicating surface disturbance at the wafer edge of the sample treated by HTA at 1730 C for 3 h. Reproduced with permission [20]. Copyright 2020, Wiley-VCH.…”

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confidence: 99%

High‐Temperature Annealing and Patterned AlN/Sapphire Interfaces

Hagedorn

Mogilatenko

Walde

et al. 2021

Physica Status Solidi (b)

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Using the example of epitaxial lateral overgrowth of AlN on trench-patterned AlN/sapphire templates, the impact of introducing a high-temperature annealing step into the process chain is investigated. Covering the open surfaces of sapphire trench sidewalls with a thin layer of AlN is found to be necessary to preserve the trench shape during annealing. Both the influence of annealing temperature and annealing duration are investigated. To avoid the deformation of the AlN/sapphire interface during annealing, the annealing duration or annealing temperature must be low enough. Annealing for 1 h at 1730 C is found to allow for the lowest threading dislocation density of 3.5 Â 10 8 cm À2 in the subsequently grown AlN, while maintaining an uncracked smooth surface over the entire 2 in. wafer. Transmission electron microscopy study confirms the defect reduction by high-temperature annealing and reveals an additional strain relaxation mechanism by accumulation of horizontal dislocation lines at the interface between annealed and nonannealed AlN. By applying a second annealing step, the dislocation density can be further reduced to 2.5 Â 10 8 cm À2 .

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“…It was grown on a high‐temperature‐annealed (HTA) AlN/sapphire template with reduced threading dislocation density (TDD). [ 29 ] A 900 nm‐thick step‐graded Al 0.93→0.69 Ga 0.07→0.31 N layer was positioned between the template and the two top layers, leading to a degree of relaxation of 14% for the studied Al 0.55 Ga 0.45 N layer. The TDD, determined by dark spot counting in CL, varied among the samples.…”

Section: Methodsmentioning

confidence: 99%

Temperature Dependence of Dark Spot Diameters in GaN and AlGaN

Netzel

Knauer

Brunner

et al. 2021

Physica Status Solidi (b)

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Threading dislocations in c‐plane (Al,Ga)N layers are surrounded by areas with reduced light generation efficiency, called “dark spots.” These areas are observable in luminescence measurements with spatial resolution in the submicrometer range. Dark spots reduce the internal quantum efficiency in single layers and light‐emitting devices. In cathodoluminescence measurements, the diameter of dark spots (full width at half maximum [FWHM]) is observed to be 200–250 nm for GaN. It decreases by 30–60% for AlxGa1−xN with x ≈ 0.5. Furthermore, the dark spot diameter increases with increasing temperature from 83 to 300 K in AlGaN, whereas it decreases in GaN. Emission energy mappings around dark spots become less smooth and show sharper features on submicrometer scales at low temperature for AlGaN and, on the contrary, at high temperature for GaN. It is concluded that charge carrier localization dominates the temperature dependence of dark spot diameters and of the emission energy distribution around threading dislocations in AlGaN, whereas the temperature‐dependent excitation volume in cathodoluminescence and charge carrier diffusion limited by phonon scattering are the dominant effects in GaN. Consequently, with increasing temperature, nonradiative recombination related to threading dislocations extends to wider regions in AlGaN, whereas it becomes spatially limited in GaN.

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Status and Prospects of AlN Templates on Sapphire for Ultraviolet Light‐Emitting Diodes

Cited by 41 publications

References 64 publications

High‐Temperature Annealing of AlGaN

High‐Temperature Annealing of AlGaN

High‐Temperature Annealing and Patterned AlN/Sapphire Interfaces

Temperature Dependence of Dark Spot Diameters in GaN and AlGaN

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