Generative Design of Stable Semiconductor Materials Using Deep Learning And DFT

Semiconductor device technology has exceptionally developed in complexity since discovering the bipolar transistor. With the rapid advancement of various technologies, semiconductors with distinct properties are essential. Recently, deep-learning, data-mining, and density functional theory (DFT)- based high-throughput calculations were widely performed to discover potential semiconductors for diverse applications. CubicGAN is a generative adversarial network where high-throughput analyses were done to uncover mechanically and dynamically stable materials with the assistance of DFT. In our work, we screened the semiconductors using a binary classifier from materials found from the CubicGAN. Next, we performed DFT computations to study their thermodynamic stability based on energy-above-hull and formation energy. According to our studies, 12 stable semiconductors were found with a particular class of materials, which we label as AA′MH6. Those are BaNaRhH6, BaSrZnH6, BaCsAlH6, SrTlIrH6, KNaNiH6, NaYRuH6, CsKSiH6, CaScMnH6, YZnMnH6, NaZrMnH6, AgZrMnH6, AgZrMnH6, and ScZnMnH6. It could be shown that AA′MH6 with M=Mn and NaYRuH6 semiconductors have considerably different structural, mechanical, and thermodynamic properties compared to the rest of the AA′MH6 semiconductors. In this study, The maximum bandgap found was approximately 3.3 eV from KNaNiH6, while the minimum bandgap was about 1.3 eV from CaScMnH6. BaNaRhH6, BaCsAlH6, CsKSiH6, KNaNiH6, and NaYRuH6 were identified as wide-bandgap semiconductors, where bandgaps are greater than 2 eV. Furthermore, BaSrZnH6 and KNaNiH6 are a direct bandgap semiconductors, whereas other AA′MH6 semiconductors exhibit indirect bandgaps.

Enhanced Light-Matter Interaction in Two-Dimensional Transition Metal Dichalcogenides

Two dimensional (2D) transition metal dichalcogenide (TMDC) materials, such as MoS2, WS2, MoSe2, and WSe2, have received extensive attention in the past decade due to their extraordinary electronic, optical and thermal properties. They evolve from indirect bandgap semiconductors to direct bandgap semiconductors while their layer number is reduced from few layers to a monolayer limit. Consequently, there is strong photoluminescence in a monolayer (1L) TMDC due to the large quantum yield. Moreover, such monolayer semiconductors have two other exciting properties: large binding energy of excitons and valley polarization. These properties make them become ideal materials for various electronic, photonic and optoelectronic devices. However, their performance is limited by the relatively weak light-matter interactions due to their atomically thin form factor. Resonant nanophotonic structures provide a viable way to address this issue and enhance light-matter interactions in 2D TMDCs. Here, we provide an overview of this research area, showcasing relevant applications, including exotic light emission, absorption and scattering features. We start by overviewing the concept of excitons in 1L-TMDC and the fundamental theory of cavity-enhanced emission, followed by a discussion on the recent progress of enhanced light emission, strong coupling and valleytronics. The atomically thin nature of 1L-TMDC enables a broad range of ways to tune its electric and optical properties. Thus, we continue by reviewing advances in TMDC-based tunable photonic devices. Next, we survey the recent progress in enhanced light absorption over narrow and broad bandwidths using 1L or few-layer TMDCs, and their applications for photovoltaics and photodetectors. We also review recent efforts of engineering light scattering, e.g., inducing Fano resonances, wavefront engineering in 1L or few-layer TMDCs by either integrating resonant structures, such as plasmonic/Mie resonant metasurfaces, or directly patterning monolayer/few layers TMDCs. We then overview the intriguing physical properties of different types of van der Waals heterostructures, and their applications in optoelectronic and photonic devices. Finally, we draw our opinion on potential opportunities and challenges in this rapidly developing field of research.

Power Electronic Converters for Microgrids

Power electronic converters are indispensable building blocks of microgrids. They are the enabling technology for many applications of microgrids, e.g., renewable energy integration, transportation electrification, energy storage, and power supplies for computing. In this chapter, the requirements, functions, and operation of power electronic converters are introduced. Then, different topologies of the converters used in microgrids are discussed, including DC/DC converters, single-phase DC/AC converters, three-phase three-wire, and four-wire DC/AC converters. The remaining parts of this chapter focus on how to optimally design and control these converters with the emerging wide-bandgap semiconductors. Correlated tradeoffs of converter efficiency, power density, and cost are analyzed using Artificial Neural Networks to find the optimal design of the converters.

Crystalization-enhanced Stability by Effectively Suppressing Pho-tooxidation Defect for Lasing Emission and Electroluminescent Device

Effectively protection against photooxidation of wide bandgap semiconductors remains a challenge that become the bottleneck on the road to commercialization. Herein, we demonstrated the crystallization effects of fluorene-based blue emitters on long-wavelength green band (g-band) defect with the well-defined organic micro/nanocrystals obtained via the self-assembly of surfactant-assisted reprecipitation methods. For the key molecule model 2,2'-bi(9,9-dipropyl)fluorene (DDC3F), the self-assembled nanorods film ex-hibits an ultrastable spectral stability without the presence of g-band emission (530 nm), and even main-tains the deep-blue emission under ultraviolet exposure (~ 3 h). In contrast, the spin-coated amorphous film shows a poor color purity with a green-index of ~ 4. Our results offer a robust evidence on the princi-ple in aggregate-enhanced stability, which is severely ignored by the general application of amorphously glassy molecules in OLED devices. In addition, the single nanorod as Fabry-Pérot (FP) optical resonator exhibits size-dependent dual wavelength lasing at 392 nm (threshold: 102 mW/cm2) and 412 nm (threshold: 216 mW/cm2), and generates the deep-blue electroluminescence in solution-processing OLED devices. The supramolecular self-assembled micro/nanocrystals strategy provides a potential platform to maintain ultrastable color purity in wide-bandgap optoelectronic device.

Boosting quantum yields in two-dimensional semiconductors via proximal metal plates

Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to the defect traps and the strong exciton-exciton interaction in TMDs has significantly limited the efficiency of exciton emission from this class of materials. Here, we show that exciton-exciton interaction in 1L-WS2 can be effectively screened using an ultra-flat Au film substrate separated by multilayers of hexagonal boron nitride. Under this geometry, induced dipolar exciton-exciton interaction becomes quadrupole-quadrupole interaction because of effective image dipoles formed within the metal. The suppressed exciton-exciton interaction leads to a significantly improved quantum yield by an order of magnitude, which is also accompanied by a reduction in the exciton-exciton annihilation (EEA) rate, as confirmed by time-resolved optical measurements. A theoretical model accounting for the screening of the dipole-dipole interaction is in a good agreement with the dependence of EEA on exciton densities. Our results suggest that fundamental EEA processes in the TMD can be engineered through proximal metallic screening, which represents a practical approach towards high-efficiency 2D light emitters.

GeSnOI mid-infrared laser technology

GeSn alloys are promising materials for CMOS-compatible mid-infrared lasers manufacturing. Indeed, Sn alloying and tensile strain can transform them into direct bandgap semiconductors. This growing laser technology however suffers from a number of limitations, such as poor optical confinement, lack of strain, thermal, and defects management, all of which are poorly discussed in the literature. Herein, a specific GeSn-on-insulator (GeSnOI) stack using stressor layers as dielectric optical claddings is demonstrated to be suitable for a monolithically integration of planar Group-IV semiconductor lasers on a versatile photonic platform for the near- and mid-infrared spectral range. Microdisk-shape resonators on mesa structures were fabricated from GeSnOI, after bonding a Ge0.9Sn0.1 alloy layer grown on a Ge strain-relaxed-buffer, itself on a Si(001) substrate. The GeSnOI microdisk mesas exhibited significantly improved optical gain as compared to that of conventional suspended microdisk resonators formed from the as-grown layer. We further show enhanced vertical out-coupling of the disk whispering gallery mode in-plane radiation, with up to 30% vertical out-coupling efficiency. As a result, the GeSnOI approach can be a valuable asset in the development of silicon-based mid-infrared photonics that combine integrated sources in a photonic platform with complex lightwave engineering.

Topical Review: Pathways toward cost-effective single-junction III-V solar cells

III-V semiconductors such as InP and GaAs are direct bandgap semiconductors with significantly higher absorption compared to silicon. The high absorption allows for the fabrication of thin/ultra-thin solar cells, which in turn permits for the realization of lightweight, flexible, and highly efficient solar cells that can be used in many applications where rigidity and weight are an issue, such as electric vehicles, the internet of things, space technologies, remote lighting, portable electronics, etc. However, their cost is significantly higher than silicon solar cells, making them restrictive for widespread applications. Nonetheless, they remain pivotal for the continuous development of photovoltaics. Therefore, there has been a continuous worldwide effort to reduce the cost of III-V solar cells substantially. This topical review summarises current research efforts in III-V growth and device fabrication to overcome the cost barriers of III-V solar cells. We start the review with a cost analysis of the current state-of-art III-V solar cells followed by a subsequent discussion on low-cost growth techniques, substrate reuse, and emerging device technologies. We conclude the review emphasizing that to substantially reduce the cost-related challenges of III-V photovoltaics, low-cost growth technologies need to be combined synergistically with new substrate reuse techniques and innovative device designs.

Decoration of Ag Nanoparticle on ZnO Nanowire by Intense Pulsed Light and Enhanced UV Photodetector

Zinc oxide (ZnO) nanowires (NWs) are wide-bandgap semiconductors that absorb ultraviolet (UV) radiation. Various post-treatment processes have been studied to improve the optical properties of the as-grown ZnO NWs. Among them, Ag nanoparticles (NPs) effectively improved the optical properties on the surface of the ZnO NWs. In this study, ZnO NWs were synthesized via the hydrothermal synthesis method. ZnO NWs were decorated with Ag NPs on the surface of the ZnO NWs in a silver nitrate (AgNO3) aqueous solution by intense pulsed light (IPL) irradiation. Ag NPs were successfully decorated under the following conditions: aqueous AgNO3 solution of 100 nM, an energy of 1 J/cm2, and an exposure time of 8 ms. The responsivity and sensitivity of the ZnO NW UV photodetectors increased by 7.43 and 3.37 times, respectively. The IPL process makes it possible to decorate Ag NPs in a simple manner within an extremely short time.