The role of surface roughness on dislocation bending and stress evolution in low mobility AlGaN films during growth

Bardhan, Abheek; Mohan, Nagaboopathy; Chandrasekar, Hareesh; Ghosh, Priyadarshini; Rao, D.V. Sridhara; Raghavan, Srinivasan

doi:10.1063/1.5005080

Cited by 14 publications

(6 citation statements)

References 34 publications

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“…A smooth surface indicates good mechanism of dislocation bending (Bardhan, 2018). Figure 1 shows the root-mean-square (RMS) roughness for the surface of the AlN layer grown with different nucleation thickness, as investigated under AFM measurement.…”

Section: Resultsmentioning

confidence: 99%

Effect of nucleation layer thickness on reducing dislocation density in AlN layer for AlGaN-based UVC LED

Samsudin

Mohd-Yusuf

Zainal

et al. 2021

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Purpose The purpose of this study is to investigate the influence of AlN nucleation thickness in reducing the threading dislocations density in AlN layer grown on sapphire substrate. Design/methodology/approach In this work, the effect of the nucleation thickness at 5 nm, 10 nm and 20 nm on reducing the dislocation density in the overgrown AlN layer by metal organic chemical vapor deposition was discussed. The AlN layer without the nucleation layer was also included in this study for comparison. Findings By inserting the 10 nm thick nucleation layer, the density of the dislocation in the AlN layer can be as low as 9.0 × 108 cm−2. The surface of the AlN layer with that nucleation layer was smoother than its counterparts. Originality/value This manuscript discussed the influence of nucleation thickness and its possible mechanism in reducing dislocations density in the AlN layer on sapphire. The authors believe that the finding will be of interest to the readers of this journal, in particular those who are working on the area of AlN.

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Section: Resultsmentioning

confidence: 99%

Effect of nucleation layer thickness on reducing dislocation density in AlN layer for AlGaN-based UVC LED

Samsudin

Mohd-Yusuf

Zainal

et al. 2021

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“…An unbiased 2D charge density of about 10 13 cm −2 typically forms at the AlGaN/GaN interface. Further information on growth is given elsewhere [26,27]. The graphene monolayer was grown on Cu foils using a home-made CVD system with methane and hydrogen as source gases.…”

Section: Resultsmentioning

confidence: 99%

Quantum capacitance of coupled two-dimensional electron gases

Balasubramanian

2021

J. Phys.: Condens. Matter

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Quantum capacitance effect is observed in nanostructured material stacks with quantum limited density of states. In contrast to conventional structures where two-dimensional electron gases (2DEG) with reduced density of states interact with a metal plate, here we explore the quantum capacitance effect in a unique structure formed by two 2DEG in a graphene sheet and AlGaN/GaN quantum well. The total capacitance of the structure depends non-linearly on the applied potential and the linear density of states in graphene leads to enhanced electric field leakage into the substrate causing a dramatic 50% drop in the overall capacitance at low bias potentials. We show theoretical projections of the quantum capacitance effect in the proposed device stack, fabricate the structure and provide experimental verification of the calculated values at various temperatures and applied potentials. The wide swing in the total capacitance is sensitive to the chemical potential of the graphene sheet and has multiple applications in molecular sensing, electro-optics, and fundamental investigations.

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“…19 The gradient of composition in the AlGaN layer leads to a large compressive stress in the overgrown GaN layer due to the gradual change of the lattice parameters and the thermal expansion coefficient from the AlN seed layer grown on Si(111) to the GaN layer. It has been shown 20 that dislocations are more prone to bend and relax the compressive stresses when the dislocation lines intersect a smooth surface; however, this is followed by cracking of the graded AlGaN layer on Si. An improvement of the crystal quality of N-polar GaN layers with a pseudomorphically grown graded AlGaN interlayer on GaN(0001) was reported in ref 21.…”

Section: Introductionmentioning

confidence: 99%

Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers

Stanchu

Kuchuk

Mazur

et al. 2018

Crystal Growth & Design

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Plastic strain relaxation in epitaxial layers is one of the crucial factors that limits the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consistent with compressive strain induced in the GaN-cap layers. Finally, the localized stress and the densities of threading dislocations are correlated with the features of the resulting fractured heterostructures. These results are important toward the control of complex plastic strain relaxation and further facilitate the growth of high quality compositionally graded AlGaN-based devices.

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The role of surface roughness on dislocation bending and stress evolution in low mobility AlGaN films during growth

Cited by 14 publications

References 34 publications

Effect of nucleation layer thickness on reducing dislocation density in AlN layer for AlGaN-based UVC LED

Effect of nucleation layer thickness on reducing dislocation density in AlN layer for AlGaN-based UVC LED

Quantum capacitance of coupled two-dimensional electron gases

Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers

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