Heteroepitaxy of Semiconductors

Ayers, J. E.; Kujofsa, Tedi; Rago, Paul J.; Raphael, Johanna

doi:10.1201/9781315372440

Cited by 52 publications

(34 citation statements)

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“…The lattice mismatch between MoS 2 and HOPG can be defined using the simple formula f ¼ asÀae ae , where a s and a e are the lattice constant of the substrate and the over-layer, respectively. 41 In the MoS 2 /HOPG case, the mismatch is quite large: (0.246-0.315 nm)/ 0.315 nm = 22%. However, the strain energy could be reduced by skewed stacking the MoS 2 and HOPG.…”

Section: Discussionmentioning

confidence: 97%

Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

Butler

Huang

et al. 2017

npj 2D Mater Appl

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This report presents a series of low-temperature (4.5 K) scanning tunneling microscopy and spectroscopy experimental results on monolayer MoS 2 deposited on highly oriented pyrolytic graphite using chemical vapor deposition. To reveal the detailed connection between atomic morphology and conductivity in twisted MoS 2 /graphite heterojunctions, we employ high-sensitivity tunneling spectroscopy measurements by choosing a reduced tip-sample distance. We discern previously unobserved conductance peaks within the band gap range of MoS 2 , and by comparing the tunneling spectra from MoS 2 grains of varying rotation with respect to the substrate, show that these features have small but non-negligible dependence on the moiré superstructure. Furthermore, within a single moiré supercell, atomically resolved tunneling spectroscopy measurements show that the spectra between the moiré high and low areas are also distinct. These in-gap states are shown to have an energy shift attributed to their local lattice strain, matching corresponding behavior of the conduction band edge, and we therefore infer that these features are intrinsic to the density of states, rather than experimental artifacts, and attribute them to the twisted stacking and local strain energy of the MoS 2 /graphite heterointerface.

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Section: Discussionmentioning

confidence: 97%

Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

Butler

Huang

et al. 2017

npj 2D Mater Appl

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“…Given the 8% lattice mismatch as well as the 84% difference in thermal expansion coefficient, growing InP directly on silicon typically results in a large density of misfit and threading dislocations, detrimental for optoelectronic devices 15 . A common approach to accommodate the mismatch uses a several micrometer thick buffer layer [28][29][30] .…”

Section: Fabricationmentioning

confidence: 99%

“…However, considerable hurdles need to be overcome. When directly growing III-V semiconductors on silicon substrates, the large lattice mismatch (εInP/Si = 8.06 %), the difference in thermal expansion and the different polarity of the materials result in large densities of crystalline defects including misfit and threading dislocations, twins, stacking faults and anti-phase boundaries, strongly degrading the performance and reducing the lifetime of any device fabricated in the as-grown layers 15 . Several routes to overcome these issues have been proposed.…”

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confidence: 99%

Room-temperature InP distributed feedback laser array directly grown on silicon

et al. 2015

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These authors contributed equally to this work.Fully exploiting the silicon photonics platform requires a fundamentally new approach to realize high-performance laser sources that can be integrated directly using wafer-scale fabrication methods. Direct band gap III-V semiconductors allow efficient light generation but the large mismatch in lattice constant, thermal expansion and crystal polarity makes their epitaxial growth directly on silicon extremely complex. Here, using a selective area growth technique in confined regions, we surpass this fundamental limit and demonstrate an optically pumped InP-based distributed feedback (DFB) laser array grown on (001)-Silicon operating at room temperature and suitable for wavelength-division-multiplexing applications. The novel epitaxial technology suppresses threading dislocations and anti-phase boundaries to a less than 20nm thick layer not affecting the device performance. Using an in-plane laser cavity defined by standard top-down lithographic patterning together with a high yield and high uniformity provides scalability and a straightforward path towards cost-effective cointegration with photonic circuits and III-V FINFET logic.The potential of leveraging well-established and high yield manufacturing processes developed initially by the electronics industry has been the main driver fueling the massive research in silicon photonics over 2 the last decade [1][2][3][4][5][6] . From the start of its development though the lack of efficient optical amplifiers and laser sources monolithically integrated with the silicon platform inhibited the widespread adoption in high-volume applications. Solutions relying on flip-chipping prefabricated laser diodes 7,8 or bonding III-V epitaxial material [9][10][11] are now being deployed in commercially available optical interconnects but are less compatible with standard high-volume and low cost manufacturing processes. Approaches focusing on the engineering of group IV materials have achieved optical gain but still require extensive work to reach room temperature lasing at reasonable efficiency [12][13][14] . Therefore, the monolithic integration of direct bandgap III-V semiconductors, well known to be efficient light emitters, with the silicon photonics platform is heavily investigated. However, considerable hurdles need to be overcome. When directly growing III-V semiconductors on silicon substrates, the large lattice mismatch (εInP/Si = 8.06 %), the difference in thermal expansion and the different polarity of the materials result in large densities of crystalline defects including misfit and threading dislocations, twins, stacking faults and anti-phase boundaries, strongly degrading the performance and reducing the lifetime of any device fabricated in the as-grown layers 15 . Several routes to overcome these issues have been proposed. GaP-related materials can be grown on exact (001) silicon substrates with a small lattice mismatch and pulsed laser oscillation around 980 nm up to 120 K 16 has been achieved but shifting the laser...

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“…Depending on both the nature of the substrate and the deposition conditions, porphyrins can give rise to a multitude of aggregate morphologies, ranging from 1-D nanowires to 2-D nanoplatelets and 3-D nanocrystallites . In the framework of classical modes of film growth, the layer-plus-island (Stranski–Krastanov) progression is the most recurrent in organic overlayers deposited on crystalline substrates. , This occurrence is motivated by the fact that a perfect commensurism between the substrate surface lattice and the molecular organic overlayer is hardly attained. Hence, the strict 2-D growth of the overlayer, when it occurs, is confined to one to three monolayers. − As a whole, this is referred to as the wetting layer : efforts in its identification and study constitute a recent topic of significant debates. , In the case of porphyrins, due to their discoidal shape, the wetting layer can be constituted by molecules arranged edge-on or flat-on.…”

mentioning

confidence: 99%

Uniaxial Alignment of a Monolayer of Flat-on Free-Base Porphyrins on an Exfoliable Insulating Substrate

et al. 2019

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Porphyrins are an extremely valuable class of molecules engaged in a variety of roles spanning from biology to optoelectronics. Manipulation of the chemical and physical properties of the inner cavity of porphyrins has been recognized as crucial for the exploitation of these systems in organic devices, particularly when porphyrins self-organize at the interface with a flat-on orientation of the macrocycle. Such an orientation has been mostly observed on metallic surfaces. Unfortunately, the physical-chemical properties of the molecules result in being largely perturbed due to the molecule–metal interaction. In addition, conducting substrates are unsuited to exploit electrically driven devices based on organic layers. To overcome these issues, we performed a topology-based analysis of insulating organic single crystal structures to identify a surface which (i) ensures easy exfoliation through mechanical methods, (ii) ensures epitaxial match with an overlayer of close-packed flat-on porphyrin molecules, and (iii) displays chirality. The outcome of this work is represented by a unique crystal of mixed 2,5-diketopiperazine and fumaric acid in a 1:1 ratio. We demonstrate that the (110) surface of this crystal fulfills the aforementioned requirements and, thanks to its peculiar subnanometric corrugations, allows one to grow uniaxially aligned monolayers of flat-on porphyrin molecules assembled through van der Waals interactions.

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Heteroepitaxy of Semiconductors

Cited by 52 publications

References 0 publications

Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

Room-temperature InP distributed feedback laser array directly grown on silicon

Uniaxial Alignment of a Monolayer of Flat-on Free-Base Porphyrins on an Exfoliable Insulating Substrate

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