Photoluminescence studies of cubic GaN epilayers

Church, Stephen; Hammersley, Simon; Mitchell, P.W.; Kappers, Menno J.; Sahonta, S.‐L.; Frentrup, Martin; Nilsson, Daniel; Ward, Peter; Shaw, L. J.; Wallis, D. J.; Humphreys, C. J.; Oliver, Rachel A.; Binks, David J.; Dawson, Philip E.

doi:10.1002/pssb.201600733

Cited by 20 publications

(22 citation statements)

References 32 publications

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“…None of the G-samples show any emission at 386 nm which is related to the GaN zinc blende crystal phase 3,42 . Unlike the reference sample, the GaN nanocolumn samples G1 and G3 do not display any shoulder peak at 369 nm, which is attributed to excitons bound to structural defects 43 .…”

Section: Resultsmentioning

confidence: 91%

The influence of AlN buffer layer on the growth of self-assembled GaN nanocolumns on graphene

Mulyo

Rajpalke

Vullum

et al. 2020

Sci Rep

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GaN nanocolumns were synthesized on single-layer graphene via radio-frequency plasma-assisted molecular beam epitaxy, using a thin migration-enhanced epitaxy (MEE) AlN buffer layer as nucleation sites. Due to the weak nucleation on graphene, instead of an AlN thin-film we observe two distinguished AlN formations which affect the subsequent GaN nanocolumn growth: (i) AlN islands and (ii) AlN nanostructures grown along line defects (grain boundaries or wrinkles) of graphene. Structure (i) leads to the formation of vertical GaN nanocolumns regardless of the number of AlN MEE cycles, whereas (ii) can result in random orientation of the nanocolumns depending on the AlN morphology. Additionally, there is a limited amount of direct GaN nucleation on graphene, which induces nonvertical GaN nanocolumn growth. The GaN nanocolumn samples were characterized by means of scanning electron microscopy, transmission electron microscopy, high-resolution X-ray diffraction, room temperature micro-photoluminescence, and micro-Raman measurements. Surprisingly, the graphene with AlN buffer layer formed using less MEE cycles, thus resulting in lower AlN coverage, has a lower level of nitrogen plasma damage. The AlN buffer layer with lowest AlN coverage also provides the best result with respect to high-quality and vertically-aligned GaN nanocolumns. Recent progresses in the growth of GaN thin-film on graphene 1-6 increasingly justify the possibility for graphene to be a good alternative substrate over the available conventional substrates, for instance Si 7,8 , SiC 9 and sapphire 10. It is also reported that GaN thin-film is achievable on sapphire or amorphous substrates by employing either multi-layer or single-layer graphene as buffer layer 11-14. Such exploitations can be realized by taking advantage of the weak quasi-van der Waals binding 15-17 which can drastically relax the lattice matching condition to be satisfied by constituent materials. That being said, the lack of chemical reactivity of graphene and its extremely low surface energy 18 greatly disrupt the nucleation process of GaN, resulting in a low nucleation density 19 and difficulty in controlling the stacking sequence of the GaN growth 3. The latter issue, which often manifests in the form of stacking faults 3,5 or threading dislocations 1,4,17 , can possibly be suppressed by growing nanowire or nanocolumn structures 16,20-25. Nevertheless, because of the absence of dangling bonds in graphene, nanocolumns are often aligned in non-vertical directions 26-28 and/or have low density 27,29. Both problems are required to be addressed in order to demonstrate that the growth of III-N semiconductor nanostructures, particularly nanocolumns, utilizing graphene as the substrate can be further considered as an alternative platform in enabling the advancement of optoelectronic device performance and functionality, for instance light-emitting diodes 30. In this regard, the introduction of defects in graphene by means of plasma treatments could alleviate the issue of absence of dangling...

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Section: Resultsmentioning

confidence: 91%

The influence of AlN buffer layer on the growth of self-assembled GaN nanocolumns on graphene

Mulyo

Rajpalke

Vullum

et al. 2020

Sci Rep

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“…However, metastable zb-GaN suffers from a high density of {111} stacking faults (SFs) when grown on GaAs 1,2 , 3C-SiC 3, 4 and patterned 3C-SiC/Si 5 substrates. Such SFs are the dominant planar defect in zb-GaN and may negatively impact the optical and electronic properties of the material 6,7 . The SFs often originate from heteroepitaxial interfaces, where defects are generated to compensate for the lattice mismatch between the different materials.…”

Section: Introductionmentioning

confidence: 99%

Investigation of stacking faults in MOVPE-grown zincblende GaN by XRD and TEM

Lee

Frentrup

Vacek

et al. 2019

Journal of Applied Physics

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X-ray diffraction and bright-field transmission electron microscopy are used to investigate the distribution and density of {111}-type stacking faults (SFs) present in a heteroepitaxial zincblende GaN epilayer with high phase purity, grown on a 3C-SiC/Si (001) substrate by metalorganic vapour-phase epitaxy. It is found that the 4° miscut towards the [110] direction of the substrate, that prevents the formation of undesirable antiphase domains, has a profound effect on the relative densities of SFs occurring on the different {111} planes. The two orientations of SFs in the [-110] zone, where the SF inclination angle with the GaN/SiC interface is altered by the 4° miscut, show a significant difference in density, with the steeper (111) SFs being more numerous than the shallower (-1-11) SFs by a factor of ~ 5 at 380 nm from the GaN/SiC interface. In contrast, the two orientations of SFs in the [110] zone, which is unaffected by the miscut, have densities comparable with the (-1-11) SFs in the [-110] zone. A simple model, simulating the propagation and annihilation of SFs in zincblende GaN epilayers, reproduces the presence of local SF bunches observed in TEM data. The model 2 also verifies that a difference in the starting density at the GaN/SiC interface of the two orientations of intersecting {111} SFs in the same zone reduces the efficiency of SF annihilation. Hence, (111) SFs have a higher density compared with SFs on the other three {111} planes, due to their preferential formation at the GaN/SiC interface caused by the miscut.

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“…Recent work on a sample of zb-GaN grown on 3C-SiC reported the observation of a broad emission that encompasses the bandgaps of zb and wz-GaN and extending as far as 3.6 eV. It was suggested that carrier confinement around a high density of SFs was responsible for the band 20 . In this paper we report further investigations into the nature of the high energy emission band (HEB) in zbGaN epilayers via an investigation of the luminescence of an epilayer grown using metal-organic chemical vapour deposition (MOCVD) onto 3C-SiC/Si (001) substrates.…”

Section: Introductionmentioning

confidence: 99%

“…To investigate this, the conduction and valence band alignments were calculated in a bunch of identically spaced SFs, each treated as a 3 monolayer thick (equal to 0.78 nm) layer of wz-GaN, using the method discussed in our previous work 20 . In this model, a type II band alignment is assumed, with band offsets of 270 meV and 70 meV for the conduction and valence bands 35 .…”

Section: B Modelling Of Sfsmentioning

confidence: 99%

“…Alternatively, GaN can be grown in the [001] direction of the zincblende (zb) crystal phase, which has increased symmetry when compared to wz-GaN, resulting in zero polarisation field across the QWs 11 . Heteroepitaxial growth of zb-GaN can be performed upon 3C-SiC/Si (001) substrates [12][13][14][15][16][17][18][19][20] , which offers the advantages of being commercially viable and having a relatively small lattice mismatch of 3.7 % with GaN 21 . However, growing phase-pure zb-GaN is challenging with epilayers often containing wz-GaN, as either stacking faults (SFs) or crystal inclusions, which has been reported to reduce the radiative efficiency of zb-GaN based QW structures 22 .…”

Section: Introductionmentioning

confidence: 99%

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Effect of stacking faults on the photoluminescence spectrum of zincblende GaN

Church

Hammersley

Mitchell

et al. 2018

Journal of Applied Physics

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The photoluminescence spectra of a zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time.

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Photoluminescence studies of cubic GaN epilayers

Cited by 20 publications

References 32 publications

The influence of AlN buffer layer on the growth of self-assembled GaN nanocolumns on graphene

The influence of AlN buffer layer on the growth of self-assembled GaN nanocolumns on graphene

Investigation of stacking faults in MOVPE-grown zincblende GaN by XRD and TEM

Effect of stacking faults on the photoluminescence spectrum of zincblende GaN

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