Spatially resolved optical emission of cubic GaN/AlN multi-quantum well structures

Journal of Crystal Growth

Frentrup

Vacek

et al. 2019

Cubic zincblende (zb-)GaN nucleation layers (NLs) grown by MOVPE on 3C-SiC/Si substrates were studied to determine their optimal thickness for subsequent zb-GaN epilayer growth. The layers were characterised by atomic force microscopy, X-ray diffraction and scanning transmission electron microscopy. The as-grown NLs, with nominal thicknesses varying from 3 nm to 44 nm, consist of small grains which are elongated in the [1-10] direction, and cover the underlying SiC surface almost entirely. Thermal annealing of the NLs by heating in a H2/NH3 atmosphere to the elevated epilayer growth temperature reduces the substrate coverage of the films that are less than 22 nm thick, due to both material desorption and the ripening of islands. The compressive biaxial in-plane strain of the NLs reduces with increasing NL thickness to the value of relaxed GaN for a thickness of 44 nm. Both the as-grown and annealed NLs are crystalline and have high zincblende phase purity, but contain defects including misfit dislocations and stacking faults. The zb-GaN epilayers 2 grown on the thinnest NLs show an enhanced fraction of the wurtzite phase, most likely formed by nucleation on the exposed substrate surface at elevated temperature, thus dictating the minimum NL thickness for phase-pure zb-GaN epilayer growth.

Section: Introductionmentioning

confidence: 99%

Investigation of MOVPE-grown zincblende GaN nucleation layers on 3C-SiC/Si substrates

Journal of Crystal Growth

Frentrup

Vacek

et al. 2019

“…The choice of substrate is vital to ensure zincblende GaN growth. The main substrates that have been studied include cubic GaAs (001) (by MBE [10][11][12][13][14] and MOVPE [15][16][17][18][19][20][21]), 3C-SiC (by MBE [22][23][24][25][26] and MOVPE [27]), 3C-SiC on Si by MBE [28][29][30][31][32][33], patterned 3C-SiC on Si [34] and patterned Si [35][36][37] substrates. Some of the substrate properties to consider are lattice matching and difference in thermal expansion coefficient with zincblende GaN and cost.…”

Section: Zincblende Gan Growth Methodsmentioning

confidence: 99%

“…Stacking faults in zincblende GaN have been consistently found to lie on the {111} planes when grown on both GaAs [49,50], 3C-SiC [26,32] and patterned 3C-SiC/Si [34] substrates. The prevalence of stacking faults in zincblende GaN is likely due to stacking faults having the same stacking sequence as the wurtzite structure, which is more thermodynamically stable than the zincblende structure.…”

Section: Crystal Defectsmentioning

confidence: 99%

Cubic zincblende gallium nitride for green-wavelength light-emitting diodes

Materials Science and Technology

2017

Gallium nitride (GaN)-based light-emitting diodes (LEDs) are highly energy efficient and their widespread usage in lighting can induce significant worldwide electricity savings. To achieve white and colour-tuneable lighting, the mixing of light from red-, blue- and green-wavelength LEDs is desired. At present, the efficiency of green-wavelength LEDs is only about half of that of red- and blue-wavelength LEDs, which is also known as the ‘green gap’ problem. Cubic zincblende GaN has the potential to bridge the ‘green gap’ due to the theoretical absence of internal electric fields that plague the commonly used c-plane hexagonal wurtzite structure. This review first looks at the various methods of achieving metastable zincblende GaN, and examines the crystal defects present. Then the different components towards a full zincblende GaN LED structure, including p- and n-type doping, zincblende InGaN and AlGaN on GaN heterostructures, together with the problems that need to be overcome to achieve green-wavelength emissions are reviewed. This review was submitted as part of the 2017 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged

“…As there are no native substrates for zb III-nitride epitaxy, foreign substrates such as GaAs, [2][3][4] 3C-SiC, 5,6 and micro-structured Si (001) 7 are used instead. In all these cases, the GaN epilayer suffers from a high density of stacking faults (SFs).…”

Section: Introductionmentioning

confidence: 99%

Defect structures in (001) zincblende GaN/3C-SiC nucleation layers

Vacek

Frentrup

Journal of Applied Physics

et al. 2021

The defect structure of zincblende GaN nucleation layers grown by metalorganic vapor-phase epitaxy on 3C-SiC/Si (001) was investigated by high-resolution scanning transmission electron microscopy. Perfect dislocations, partial dislocations, and stacking faults are present in the layers. Perfect dislocations are identified as 60° mixed-type and act as misfit dislocations to relieve the compressive lattice mismatch strain in GaN. Stacking faults are mainly bounded by 30° Shockley partial dislocations and rarely by Lomer-Cottrell partial dislocations, both of which are able to relieve the compressive lattice mismatch strain in the layer. We propose that the stacking faults and their partial dislocations originate from the dissociation of perfect dislocations present in the zincblende GaN layer, and by direct nucleation of partial dislocations loops from the surface. These are the two main mechanisms, which lead to the final defect structure of the zincblende GaN nucleation layers.