This PDF file contains the front matter associated with SPIE Proceedings Volume 12651, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

X-ray photoelectron spectroscopy confirmed (XPS) that Nb substitutes on W lattice sites yielding substitutional extrinsic p-type doping in pulsed laser deposited (PLD) few-layer WS₂:Nb films. A Fermi level separation of 0.31 eV from the valence band edge with 0.5 atomic % of Nb doping was measured by ultraviolet photoelectron spectroscopy (UPS), which decreased to 0.18 eV when doping was increased to 1.1 atomic %. The corresponding hole sheet concentrations increased from 3.9 x 10¹² to 8.6 x 10¹³ cm^-2 respectively while the mobility exhibited the opposite trend, presumably due to increased ionized impurity scattering. Separately, undoped PLD few-layer WS₂ films exhibited a conductivity switch from n to p-type when the composition changed from sulfur-deficient to sulfur-rich. UPS revealed a workfunction increase from 3.36 to 4.52 eV and a corresponding change in the Fermi level separation from the valence band edge. The intrinsic p-type conductivity is assigned to excess sulfur in the form of interstitials. Despite the relatively large change in workfunction in these films, Ohmic contacts were obtained to both the n and p-type materials with indium, albeit with different contact resistances. This suggests that in addition to the interfacial energy barrier, tunneling from gap states associated with point defects and surface contamination are likely contributors to charge injection. The approach demonstrates the potential of PLD for controlled doping and the creation of p-n junctions from transition metal dichalcogenides.

Extensive research has been conducted on the negative differential resistance (NDR) behavior in various electronic applications. Theoretical simulations suggest that defects in monolayer 2D materials could impact the NDR phenomenon. In this study, we experimentally validated this theoretical prediction using straightforward fabrication methods on monolayer MoS₂. To create MoS₂ transistors with a specific amount of sulfur vacancy, we employed techniques such as KOH solution treatment, electron beam irradiation, and chemical vapor deposition (CVD) using low sulfur supply. Through comprehensive analysis of the devices' electrical characteristics and spectroscopic examination, we successfully observed the NDR in the defective monolayer MoS₂ field-effect transistors (FETs) with approximately 5% sulfur vacancy, as confirmed by x-ray photoelectron spectroscopy (XPS). Moreover, this NDR effect remains stable and can be controlled by the gate electric field or light intensity at room temperature. This discovery suggests that the NDR effect in monolayer MoS₂ transistors holds promising potential for future electronic applications.

A compact assembly of photodetectors, enhanced with innovative surface nanostructures, can significantly enhance imaging modalities. This advancement captures multi-dimensional data, including spectral profiles, temporal responses, and spatial resolution. Achieving this breakthrough centers on the meticulous engineering of individual ultrafast detectors, which exhibit diverse responses to identical illumination conditions. A pivotal role is played by the integration of artificial intelligence (AI)-driven computational imaging, which optimizes the obtained multi-dimensional data. This paper demonstrates the benefits of such an imaging method. Specifically, we highlight the potential reductions in the physical scale of current systems, significant enhancements in system sensitivity, and substantial cost reduction. The potential applications include molecular fluorescence signal detection, chem-biological imaging, advanced LiDAR systems, and state-of-the-art focal plane arrays.

The accelerated advancements in nanophotonic technologies have amplified the requirements for optoelectronic devices. These now encompass the need for compact design, rapid operation, enhanced efficiency, and reduced power consumption. Meeting these evolving demands necessitates the development of innovative material frameworks aligned with emerging technological standards. In this context, we unveil our latest research findings, accentuating the exploitation of low-dimensional materials to pioneer advancements in photodetector and electro-optic modulator functionalities. Drawing from the emergent field of ’strainoptronics’ our work elucidates its capability to modulate a variety of material properties: bandgap, work function, and mobility. Moreover, harnessing the principles of the scaling-length theory, we chart our progression and empirical outcomes related to high gain-bandwidth product photodetectors. This encompasses the amalgamation of a metal slot with a silicon photonic waveguide aimed at refining the carrier-lifetime-to-transit time ratio. Additionally, our 2D material PN junction photodetector, operable at zero bias, emerges as a vanguard in curtailing dark currents, resulting in remarkably efficient noise-equivalent power outputs. Furthermore, recognizing the surging interest in wearable technology, our research also delves into the integration of these advancements into flexible substrates. We also elucidate the symbiotic relationship between our innovations and Photonic Integrated Circuits (PICs), highlighting the potential for our developments to serve as foundational building blocks for the next generation of compact, efficient, and integrative PICs. Our research presents a confluence of innovative approaches and material amalgamations, poised to redefine optoelectronic device performance in tandem with contemporary nanophotonic paradigms and the dynamic landscape of wearable technology and integrated photonic circuits.

In recent years, ultra-thin quasi-2D (<4nm) oxide semiconductor (OS)-based transistors are promising for future high performance electronic and photoelectronic. For such applications, precise tuning of doping concentration of semiconductor with a wide tunable window is of critical importance. However, in practical electronic circuits is limited by the relative lack of doping modulation with fine control over wide bandwidths. Here, the doping concentration of ultra-thin OS transistor is precisely tuned over a range, corresponding to a shift of threshold voltage change of more than 10 V using thermal annealing combined with laser illumination. Due to the strong surface effect, the ultra-thin OS would be highly sensitive to ambient atmosphere. The gas absorption process makes us could dramatically change the carrier concentration of OS by introducing laser to the system. This work highlights the importance of tunable threshold voltage and the mechanism of the transition process. The tunability of doping concentration in ultra-thin OS-based transistors opens up a new path toward high performance logic circuits and other practical applications.

Anisotropic etching silicon (Si) is an active area of research for applications including energy storage (Enovix), energy conversion (photovoltaics), and now for x-ray phase contrast imaging (XPCI) diffraction gratings. Previously, a lack of control over precise alignment of the etch pattern to crystal planes and the constant evolution of hydrogen bubbles inhibited uniformity and limited the potential for higher aspect ratios. Sandia National Laboratories has made significant advancements in anisotropic silicon etching, including improvements to accurate crystal alignment using new equipment capabilities and methods of liberating hydrogen bubbles trapped in deep trenches. The possibility of reaching aspect ratios of 600:1 using anisotropic wet etching in Si have been cited in literature, but we have found no evidence of such aspect ratios being achieved. Our process is focused on improvements to yield, better anisotropy and uniformity, enabling gratings with aspect ratios as high as 170:1. The well-defined sharp edges and deep trenches that can be achieved using this technique make it a suitable method for optical grating fabrication. Deeper trenches support pushing XPCI to higher x-ray energies, which will allow access to imaging thicker or denser samples, or improved image contrast at lower energies. Higher aspect ratios in the gratings will better improve sensitivity and enable higher energy systems.

Here we demonstrate Tungsten Disulfide (WS₂) integrated silicon nitride photodetector, and we experimentally tested the responsivity of 0.32 A/W. The spectroscopic results using PL and Raman mapping were used to understand strain effect on excitonic bandgap by studying characteristics like excitons, trions, E¹_2g, A¹_g and opto-electronic response. We show high potential for flexible sensors and high spectral resolution sensing.

The formation of reproducible p-type conductivity in ZnO thin films is highly challenging now a days for the fabrication of several homo/heterojunction based fully transparent opto-electronic devices. In this study, p-type P: ZnO thin films are deposited by cost-effective SOD process and then intrinsically n-type Ga₂O₃ films are deposited on it to validate the p-type conductivity of ZnO by making vertical heterojunction with n-Ga₂O₃. The ZnO thin films are deposited by RF sputtering and subsequent P-doping is done by using the SOD technique on it. This involves proximity diffusing dopants into a spin-coated film by stacking the dopant source during thermal annealing at 800◦C for four hours in the furnace. Ga₂O₃ films are deposited on the P: ZnO films by using RF sputtering technique, for making the heterojunction. The electrical measurements are performed by using current-voltage (I-V) measurements under illuminated and dark conditions. The photo-switching and responsivity are also measured on the fabricated device. It is observed that the P: ZnO/Ga₂O₃ heterojunction exhibits the photoresponse in the dual wavelength region. The corresponding two peaks of responsivity are found around 200 nm and 390 nm with the values of 68.03 A/W and 7.93 A/W (at 5 V), respectively. Such two peaks originated due to the ultra-wide bandgaps of Ga₂O₃ (4.7eV) and P: ZnO (3.1 eV). Also, such heterojunction shows a rapid switching speed under white light at 5 V (rise time: 230 ms, fall time: 163 ms) and −5 V (rise time: 83 ms, Fall time: 169 ms), which is comparable with the other reported results. Therefore, the current study demonstrates the development of highly stable and reproducible p-type P: ZnO thin films by employing SOD technique and the validation of p-type formation by fabricating P: ZnO/Ga₂O₃ heterojunctions for dual-wavelength selector UV detector application and such detectors can be a potential candidate for various optoelectronic devices.

This paper reports a comparative study of InAs/GaAs quantum dots (QDs) heterostructures with vertically aligned strain-coupled uncapped and capped buried dots, epitaxially grown by solid-state MBE. Here an in-situ method is used to optimize the band alignment among the coupled QD heterostructures. In this work, the stable uncapped QDs are grown with reduced surface energy using the self-assembly growth technique called Stranski Krastanov (SK) QDs. During growth we reduced the Indium flux to the top uncapped QDs layer referred to as Surface QDs (SQDs), keeping a constant overgrowth percentage (2.7 ML) for capped QDs known as buried QDs (BQDs). Up to 2 ML SQD, two distinguished energy states for BQD and SQD are observed, showing a gradual blue-shift as the InAs content reduces from 2.2 to 2 ML. As we get into the regime of 1.6ML, the energy states of SQD are in resonating condition with the BQDs. This resonance enhances the electronic interaction between the coupled dot layers. The corresponding photoluminescence response depicts the wave function overlapping surface and buried dots. In addition, AFM images show a homogeneous distribution in size and shape of the SQDs in this regime. Strain analysis of the heterostructure is performed by Raman spectroscopy and HRXRD measurement. The heterostructure with 1.6 ML coverage would promise a sensor based on SK-QDs with high efficiency due to inter-dot carrier communication. Here the underneath capped QD supplies surplus carriers act like a reservoir and the surface QD layers act as a primary receptor.

In the past decade, surface quantum dots (SQDs) have been thoroughly investigated for sensing applications. The SQDs suffer from the limitations of non-uniformity dot distribution and weak oscillator strength, which affect their response to ambient contaminants. We have achieved uniformity by coupling buried quantum dots (BQDs) with SQDs. Moreover, BQDs provide additional carriers to SQDs for enhancing sensitivity. In this study, we have theoretically investigated the impact of varying the capping material of BQDs on their strain and optical properties. Investigations have been carried out with three samples having different capping materials as GaAs (sample A1), InGaAs (sample A2), and InAlGaAs (sample A3). A decreasing trend in the magnitude of hydrostatic strain and an increasing trend in biaxial strain inside the BQD from samples A1-A3 is observed. With a decrease in hydrostatic strain, the conduction band eigenstate lowers towards the band edge resulting in a lowering bandgap. With an increase in biaxial strain, the bandgap lowers due to the heavy hole (HH) and light hole (LH) band splitting. The lowering of the bandgap enhances the luminescence of BQD in sample A3. The computed photo-luminescence (PL) emission wavelength is found to be 1547 nm, 1558 nm, and 1568 nm for GaAs, InAlGaAs, and InGaAs capping respectively. The lowering in the bandgap of BQD leads to band alignment between SQD and BQDs, which may improve the carrier communication between these layers and become a promising candidate for better carrier reservoirs for SQDs in sensor applications.

Vanadium disulfide (VS₂), which belongs to transition metal dichalcogenides (TMDs) group, is a prominent material for energy storage application. On the other hand, graphene like carbon-based nanomaterials offer improved electrochemical performance due to high specific surface area, excellent conductivity, good chemical, and mechanical stability. Therefore, composite of graphene like material with TMD have shown better electrochemical performance till date. In this work, we have synthesized VS₂/N-rGO composite material, which can be applicable for energy storage device. At first, we have synthesized graphene oxide (GO) using Tour method. Then we reduced GO along with nitrogen doping using hydrothermal route. After that, we have synthesized VS₂/N-rGO by hydrothermal method. The X-ray diffraction (XRD) spectrum of GO shows a prominent peak at 10.2°, which implies the interlayer spacing in GO of 8.7 Å. After reduction and doping with nitrogen (N), two peaks are obtained at 24.7° (d = 3.6 Å), and 42.3° (d = 2.1 Å) in the XRD pattern which corresponds to N-rGO. RAMAN spectrum of composite shows the characteristics peaks of VS₂ at 141.6, 194.5, 286.4, 404.1, 680.1 and 997.2 cm^-1 along with D and G bands coming from the N-rGO. We have also performed the Fourier-transform infrared-spectroscopy (FTIR) and Field-emission gun-scanning electron-microscopy (FEG-SEM) characterizations to investigate the bonding vibration and surface morphology of the materials. The synthesized material is suitable for energy storage applications.

High-performance semiconductors for optoelectronic device applications based on hybrid perovskites have been extensively investigated by the research community. However, their degradability and toxicity problem is a serious challenge that should be addressed effectively. Nowadays, double perovskites have been introduced as a promising lead-free alternative which is a combination of two single perovskites in which lead is replaced by monovalent and trivalent cation. Herein, we have chemically prepared a promising, stable, and novel organic-inorganic hybrid lead-free methyl ammonium (MA) based double perovskite material MA₂AgBiCl₆ by one-pot hydrothermal method. Structural characterization using x-ray diffraction (XRD) experiment confirms the formation of the orthorhombic crystalline phase of MA₂AgBiCl₆. Further, the examination of the Ultra-violet (UV-vis) spectroscopy characterization of MA₂AgBiCl₆ affirms the excellent absorbance behavior with a direct and indirect bandgap of 3.58 eV and 2.8 eV respectively. To investigate the optical characteristics of MA₂AgBiCl₆, photoluminescence (PL) spectroscopy experiment was performed and it is found that the material is reflecting good photoluminescence nature having a sharp peak at 320 nm which occur due to the band to band transition and carrier recombination of phonons. Furthermore, we performed a scanning electron microscopy (SEM) experiment on synthesized material to see its surface properties and we have observed the uniform nanotubes like fine and dense structure. Also, the Fourier transform infrared (FTIR) spectroscopy measurement reflect the transmittance nature of the prepared material. This detailed investigation on novel double perovskite MA₂AgBiCl₆ opens a new window for the emerging category of halide-based double perovskites for their possible utility in photovoltaics.