Transition metal dichalcogenides such as MoS2, which can be produced in monolayer form, have attracted attention because of their interesting and potentially useful electrical and optical properties. These properties often depend sensitively on material properties such as defect density and crystallinity. Herein, the effects of postgrowth annealing on monolayer MoS2 grown using a novel chemical vapor deposition process are investigated. In this process bulk molybdenum patterns serve as the nucleation site and source material for high‐quality MoS2 material growth. After postgrowth thermal annealing, the photoluminescence is found to blueshift and become more uniform up to an annealing temperature of 300 °C. At higher temperatures, isolated monolayers begin to crack along the grain boundaries, which leads to variations in luminescence, whereas after annealing temperature of 200 °C, material anchored to the molybdenum patterns is found to easily ablate.

A chemical vapor deposition (CVD) growth model is presented for a technique resulting in naturally formed 2D transition metal dichalcogenide (TMD)-based metal-oxide-semiconductor structures. The process is based on a standard CVD reaction involving a chalcogen and transition metal oxide-based precursor. Here however, a thin metal oxide layer formed on lithographically defined contacts composed of pure bulk transition metal serves as the precursor. The chalcogen reacts with the metal oxide, leading to the growth of highly crystalline films, which display strong luminescence, monolayer Raman signatures, and relatively large crystal domains. Raman spectroscopy and cross-sectional SEM studies provide insight into the characteristics of the metal oxide and its effect on the TMD growth. The TMD material migrates outward along the substrate while remaining connected to the lithographically defined contacts, offering a scalable path for producing as-grown, naturally contacted, two-dimensional material-based devices.

Coupled quantum dots (CQDs) that consist of two InAs QDs stacked along the growth direction and separated by a relatively thin tunnel barrier have been the focus of extensive research efforts. The expansion of available states enabled by the formation of delocalized molecular wavefunctions in these systems has led to significant enhancement of the already substantial capabilities of single QD systems and have proven to be a fertile platform for studying light-matter interactions, from semi-classical to purely quantum phenomena. Observations unique to CQDs, including tunable g-factors and radiative lifetimes, in situ control of exchange interactions, coherent phonon effects, manipulation of multiple spins, and nondestructive spin readout, along with possibilities such as quantum-to-quantum transduction with error correction and multipartite entanglement, open new and exciting opportunities for CQD-based photonic quantum technologies. This review is focused on recent CQD work, highlighting aspects where CQDs provide a unique advantage and with an emphasis on results relevant to photonic quantum technologies.

The hexagonal boron nitride (h-BN) as a wide bandgap semiconductor is an attractive material for deep ultraviolet (DUV) generation. In this paper we study the prospect of using the stacking hexagonal boron nitride nanosheets (h-BNNS) for generating DUV emission by impact excitation in alternating current driven thin electroluminescence devices (ACTEL) based on BN phosphors having different morphologies. A theoretical approach considered is based on the impact excitation model for generating DUV from stacking h-BNNS under a high electric field. It was found that in the h-BNNS with a thickness of 90 nm biased at 3.33×10^9 V/m, the quantum yield can reach to 86.8%, and the power conversion efficiency of 1.68%. To achieve the same quantum yield and power conversion efficiency for the ACTEL based on h-BN single crystal, the active phosphor layer should be 2 μm thick when biased at 1.5×10^8 V/m.

The difficulty of processing two-dimensional (2D) transition metal dichalcogenide (TMD) materials into working devices with any scalability is one of the largest impediments to capitalizing on their industrial promise. Here, we describe a versatile, simple, and scalable technique to directly grow self-contacted thin-film materials over a range of TMDs (MoS2, MoSe2, WS2, and WSe2), where predeposited bulk metallic contacts serve as the nucleation site for the TMD material to grow, forming naturally contacted device structures in a single step. The conditions for growth as well as optical and physical properties are reported. Because the material grows controllably around the lithographically defined patterns, wafer scale circuits and complex device geometries can be envisioned, including lateral heterostructures of different TMD materials.

We will present a chemical vapor deposition process to selectively grow 2D materials in a deterministic manner around lithographically defined bulk metallic patterns which concurrently provide asgrown electrical contact to the material [1]. With this process, monolayer films, with lateral extent of up to hundreds of microns are controllably grown on and around patterned regions of transition metals. The materials display strong luminescence, monolayer Raman signatures, and relatively large crystal domains. In addition to producing high optical quality monolayer material, the metallic patterns remain conductive providing as-grown metallic contacts to the material. Preliminary results (Figure 1) have demonstrated the feasibility of this process through the direct growth of MoS2 based metal-semiconductor-metal photodiodes and Schottky barrier FET devices. Since the material grows controllably around the lithographically defined patterns, complex device structures and wafer scale circuits can be envisioned. Preliminary results also indicate the technique has the added potential of producing self-contacted heterostructured devices as well as the possibility of controllable doping of the 2D material using alloyed metallic contacts. This is the first report of using bulk metallic patterns resulting in as-grown, self-forming, electrical contact to the monolayer material, providing a simple, scalable, and reproducible method for creating 2D materials-based devices with broad implications for basic research and industrial applications.

Scalable fabrication of two-dimensional materials-based devices with consistent characteristics remains a significant impediment in the field. Here, we report on as-grown monolayer MoS2 metal-semiconductor-metal photodetectors produced using a CVD process which results in self-contacted two-dimensional material-based devices. The photodetectors show high responsivity (∼1 A/W) even at a low drain-source voltage (VDS) of 1.5 V and a maximum responsivity of up to 15 A/W when VDS = 4 V with an applied gate voltage of 8 V. The response time of the devices is found to be on the order of 1 μs, an order of magnitude faster than previous reports. These devices demonstrate the potential of this simple, scalable, and reproducible method for creating as-grown two-dimensional materials-based devices with broad implications for basic research and industrial applications.

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 process to selectively grow 2D material in a deterministic manner around lithographically defined bulk 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 transition metals. By using different combinations of metallic pattern and oxide based 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 remain conductive and therefore have the advantage of providing as-grown metallic contacts to the material, offering a path for simple device fabrication and large scale production

Interdot transitions in the emission spectra of a quantum dot molecule may be used as a sensitive nanoscale probe to measure electric fields. Here, we demonstrate this potential by monitoring the temporal behavior of photovoltaic band flattening in a Schottky diode structure using a two-color excitation scheme. First, a continuous wave laser is tuned to an excitation energy below the wetting layer (WL) emission energy to create the interdot transition that is used to monitor the electric field in the device. A second modulated laser, at higher energy, is then used to create the optically generated electric field (OGEF) which leads to the photovoltaic band flattening. It is found that the rise time of this OGEF is ∼2.85 μs and the decay, or fall time, is on the order of ∼110 μs, most likely determined by device-dependent carrier transport, trapping, and tunneling rates. We also find that, at higher applied fields, the OGEF tends to decay faster and the measured values are consistent with the photovoltaic band-flattening effects reported previously in nanostructure devices.