Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS 2 ) and tungsten (W) doping of molybdenum diselenide (MoSe 2 ) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of two dimensional (2D) materials. To date, the impact of the doping on the structural, electronic and photonic properties of in-situ doped monolayers remains unanswered due to challenges This article is protected by copyright. All rights reserved.2 including strong film-substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, we demonstrate in-situ rhenium (Re) doping of synthetic monolayer MoS 2 with ~1 at% Re. To limit substrate-film charge transfer r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence (PL) indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the Mo-O bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re.The work presented here demonstrates that Re doping of MoS 2 is a promising route towards electronic and photonic engineering of 2D materials.

The transfer-free direct growth of high-performance materials and devices can enable transformative new technologies. Here, room-temperature field-effect hole mobilities as high as 707 cm V s are reported, achieved using transfer-free, low-temperature (≤120 °C) direct growth of helical tellurium (Te) nanostructure devices on SiO /Si. The Te nanostructures exhibit significantly higher device performance than other low-temperature grown semiconductors, and it is demonstrated that through careful control of the growth process, high-performance Te can be grown on other technologically relevant substrates including flexible plastics like polyethylene terephthalate and graphene in addition to amorphous oxides like SiO /Si and HfO . The morphology of the Te films can be tailored by the growth temperature, and different carrier scattering mechanisms are identified for films with different morphologies. The transfer-free direct growth of high-mobility Te devices can enable major technological breakthroughs, as the low-temperature growth and fabrication is compatible with the severe thermal budget constraints of emerging applications. For example, vertical integration of novel devices atop a silicon complementary metal oxide semiconductor platform (thermal budget <450 °C) has been theoretically shown to provide a 10× systems level performance improvement, while flexible and wearable electronics (thermal budget <200 °C) can revolutionize defense and medical applications.

Two-dimensional materials have shown great promise for implementation in next-generation devices. However, controlling the film thickness during epitaxial growth remains elusive and must be fully understood before wide scale industrial application. Currently, uncontrolled multilayer growth is frequently observed, and not only does this growth mode contradict theoretical expectations, but it also breaks the inversion symmetry of the bulk crystal. In this work, a multiscale theoretical investigation aided by experimental evidence is carried out to identify the mechanism of such an unconventional, yet widely observed multilayer growth in the epitaxy of layered materials. This work reveals the subtle mechanistic similarities between multilayer concentric growth and spiral growth. Using the combination of experimental demonstration and simulations, this work presents an extended analysis of the driving forces behind this non-ideal growth mode, and the conditions that promote the formation of these defects. Our study shows that multilayer growth can be a result of both chalcogen deficiency and chalcogen excess: the former causes metal clustering as nucleation defects, and the latter generates in-domain step edges facilitating multilayer growth. Based on this fundamental understanding, our findings provide guidelines for the narrow window of growth conditions which enables large-area, layer-by-layer growth.