While new species and properties of two-dimensional (2D) materials are being reported with extraordinary regularity, a significant bottleneck in the field is the ability to controllably process material into working devices. We report a chemical vapor deposition based procedure to selectively grow 2D material in a deterministic manner around lithographically defined metallic patterns which concurrently provide as-grown contacts to the material.Monolayer films, with lateral extent of up to hundreds of microns are controllably grown on and around patterned regions of bulk transition metals. By using different combinations of metallic pattern and oxide precursor, heterostructured MoS2/WS2 growth has been observed as well. The materials display strong luminescence, monolayer Raman signatures, and relatively large crystal domains. In addition to producing high optical quality monolayer material deterministically and selectively over large regions, the metallic patterns have the advantage of providing as-grown contacts to the material, offering a path for device fabrication and large scale production. 2The contemporary prominence of layered materials is driven by their technological and scientific potential in the 2D, monolayer, limit. [1,2] In addition to properties such as high mobilities, semiconducting and superconducting behavior, and excellent thermal properties, many of these materials have the potential for transformative opto-electronic applications, with large absorption, strong room-temperature emission, non-linear response, and optical control of spin and valley degrees of freedom. [3] Many seminal results of 2D material based device fabrication have involved the isolation of monolayers followed by making metal contact with the film, commonly using e-beam lithography. The customary method for isolating monolayers is micromechanical exfoliation which produces high quality crystalline flakes, on the order of up to tens of microns. However, this method provides no deterministic control over sample thickness, size, or location and provides no path to scalability. Liquid exfoliation uses ionic species as intercalating agents, which facilitates a breakdown of van der Waal forces and results in sub-micrometer sized monolayers of transition metal dichalcogenides (TMDs). [4,5] In addition to small sizes, liquid exfoliated monolayers are often found to have different structural and electronic properties, requiring further processing. [4] Chemical Vapor Deposition (CVD) has emerged as one of the most promising and preferred synthesis processes for TMD growth. [6] Two general methods of CVD growth include heating of a metal oxide powder in the presence of sulfur, [7] or direct sulfurization of thin layers of either metal or metal oxide. [8,9] Regardless of the technique used to produce monolayer TMDs, once they are grown or isolated, devices are then typically fabricated using lithography and metal deposition, which may require further processing in order to obtain useful metal-semiconductor contacts. Here we ...

The novel use of a GaAs y P1–y /GaP compressively strained superlattice (CSS) to provide enhanced control over misfit dislocation (MD) evolution and threading dislocation density (TDD) during GaP/Si metamorphic heteroepitaxy is demonstrated. Insertion of the CSS just after critical thickness, and thus prior to substantial dislocation introduction, is found to yield significantly reduced TDD in relaxed, 500 nm thick, n-type GaP/Si versus comparable control samples. The impact of CSS period count on average TDD and the overall dislocation network morphology was examined, supported by quantitative microstructural characterization, revealing a nearly 20× relative TDD reduction (to (2.4 ± 0.4) × 106 cm–2) with a 3-period CSS structure. A similarly low TDD ((3.0 ± 0.6) × 106 cm–2) is maintained when the resultant n-GaP/Si virtual substrate is used for the growth of a subsequent n-type GaAs0.75P0.25-terminal GaAs y P1–y step-graded metamorphic buffer. Although the physical mechanism for TDD reduction provided by these structures is not yet entirely understood, this initial work suggests that enhanced glide dynamics of MDs at or within the CSS placed early in the growth leads to a reduction in the total number of dislocations introduced overall, as opposed to annihilation-based reduction that occurs in conventional strained-layer superlattice dislocation filter approaches.

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Characterization of crystalline defects in semiconducting materials is crucial for the development of wellinformed growth methods and ultimately high-performance optoelectronic devices. An excellent example is the technologically important, but fundamentally complex, heteroepitaxial GaP/Si system. GaP/Si is presently under extensive consideration as an enabling materials integration pathway for the production of III-V/Si photovoltaics and optoelectronics. However, due to lattice-mismatch and interfacial heterovalency, GaP/Si growth can result in a multitude of extended defects (e.g. misfit dislocations), the control of which is critical for the performance of associated devices. To achieve the resolution necessary for characterization of such defects, transmission electron microscopy (TEM) has generally been accepted as the most viable technique. However, the extensive sample preparation required, and the relatively small resultant sample areas, can lead to characterization bottlenecks and insufficiently representative results. An alternative diffraction imaging technique, electron channeling contrast imaging (ECCI) [1]- [3], which is growing in popularity within the semiconductor epitaxy field, provides a number of inherent advantages over TEM [4]- [7]. Performed in a scanning electron microscope (SEM), ECCI enables high-throughput, non-destructive characterization of surface and subsurface defects across much larger specimens with little to no sample preparation. With ECCI it is possible to rapidly collect extremely large image sets, from which statistically relevant quantitative descriptors can nominally be extracted, enabling the determination of key defect formation and evolution properties, like dislocation dynamics. To this end, we briefly describe preliminary work on quantitative ECCI-based characterization of misfit dislocations at the GaP/Si interface using semi-automated image analysis, with the ultimate goal of providing detailed insight into the dislocation dynamics in this model system.Depending on the epitaxial processes used to produce the GaP/Si structures, the range and morphology of the resulting misfit dislocation networks can vary greatly, with densities and line lengths spanning orders of magnitude (Fig. 1). Statistically relevant quantification thus requires the use of large total image areas (0.1 mm 2 or more). In such cases, manual image analysis is highly impractical, if not effectively impossible. Therefore, we are investigating both state-of-the-art segmentation analysis, as well as machine learning approaches, toward the development of a robust set of semi-automated image analysis procedures for the extraction of a wide range of misfit dislocation statistics, which can be compared against and/or used to develop descriptive and predictive dislocation dynamics models. To date, we have had the most success with the MIPAR image analysis package [8] for batch-processed segmentation of very large area ECCI micrographs and montages. This method has yielded reliable and accurate (within 5% of...

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