Session BB06: V: Industrial and Applied Physics I

Laser-amplified nonvolatile charge trapping effect in semiconductor quantum dot structures

Non-volatile regulation by optical means has long been a challenge due to the usual volatility of photoelectric effect of light excitation. This limitation hinders the evolution of optoelectronic technologies, particularly in optical memory. Traditionally, photodetectors record only transient optical signals, relying on ancillary electronic devices for data retention and manipulation. Such multi-device integration delivers poor efficiency and high-power consumption. Thus, achieving direct nonvolatile storage and processing of light information is highly desirable, spurring tremendous research. Here, we report the discovery of a light-induced nonvolatile trapping effect that allows for highly effective and lasting storage of optical signals, in a simple two-terminal molybdenum disulfide quantum dot memory structure. Moreover, the charge trapping capability can be enhanced almost threefold after laser irradiation, in contrast to pure electrical means. We feature a new barrier modulation model driven by the synergistic action of electric pulse and laser signal. More interestingly, by designing an optoelectronic memory array, we successfully demonstrate that this effect can be applied simultaneously for image sensing and preprocessing, as well as in neuromorphic reinforcement learning. Undoubtedly, this work suggests a novel approach for designing multifunctional photoelectronic devices in AI applications.   

Including Excitonic Effects in Phonon-Mediated Relaxation in Semiconductor Nanocrystals

Accounting for the electron-hole bound state effects is necessary for an accurate description of dynamics of photo-excited semiconductor nanomaterials. Here, we use density function theory (DFT) simulation output to solve the Bethe-Salpeter equation (BSE) for singlet excitons and incorporate the BSE results for exciton states into the existing technique for phonon-mediated relaxation in nanomaterials based on reduced density matrix and Redfield theory. This results in a method that includes excitonic effects. As an application, we compute photoluminescence (PL) spectrum in several semiconductor nanocrystals.   

Density-functional theory study of the thermodynamic, Optical, and Dynamical Properties of the stable and metastable phases of MnTe

MnTe is a semiconductor phase-change material that has been shown to exhibit a reversible transition between stable and metastable states in response to Joule heating in a device structure[1]. in-situ device-based switching occurs between the (NiAs) α-MnTe and a metastable form of the high temperature β-MnTe phase, the β’-MnTe phase, due to the device structure. While the stable α-MnTe has been studied in the literature, the electronic properties of the metastable phases β‑MnTe and β’-MnTe phases are largely unknown. The wide band gap of these MnTe phases suggests they may be viable candidates for interferometric-based terahertz switching devices over more traditional phase-change materials such as Ge₂Sb₂Te₅ which suffer from large optical absorption.

We have used density-functional theory (DFT) to study the static and dynamical structure of the stable and metastable phases and report on both optical, pressure-induced and dynamic properties including simulated Raman and infrared spectra. All phases were found to be antiferromagnetic and self-consistent Hubbard U corrections were employed to correct for d-electron self-repulsion effects. The band structure and optical absorption were computed in addition to the phonon dispersion using the plane wave density-functional theory code Vasp 6. We have also calculated the infrared absorption and Raman spectra using the auxiliary codes phonopy and phono3py. The effects of temperature on both the infrared absorption and Raman spectra were accounted for by the calculation of three-phonon interactions. We have also calculated enthalpic contributions to the free energy taking into account the presence of strain on the different phases as might be present in a device structure in order to understand the role of pressure induced stability on the free energy of the stable  -MnTe phase and the metastable β-MnTe and β’-MnTe phases. In addition, we have also calculated the hypothetical energy barrier for the transition from the –MnTe phase and the metastable β’-MnTe phase using the nudged elastic band formalism.

[1] S. Mori et al.. Nat. Commun., 11(1):85, 2020.   

High Temperature Insulator using Casted Ceramic for Collaborative Robotic Gripper in Additive Manufacturing

In high temperature applications such as metal additive manufacturing, and casting, one of the barriers to automation is end effector tooling. One specific issue is with ceramic machining; it is a challenging task that makes it difficult to fabricate new tooling. Our solution is to circumvent the machining process entirely and use an aluminum oxide cast ceramic for use in high temperature collaborative robotic grippers. We developed a custom procedure to create complex features in casted ceramic using 3D printed molds. We have achieved features of through holes and counterbores with approximately 2 hours of active processing, and have characterized the materials properties for our casting conditions as follows: thermal conductivity of 5.123 W/mK, ultimate compressive strength of 45.47 MPa, modulus of rupture of 20.5 MPa, and a porosity of 6.51%. This will allow for rapid fabrication of end effector tooling, custom fit to each individual application, with high performance in extreme applications.   

Thickness-dependent Electromagnetic Interference shielding from a three-layered heterostructure of TMDs and carbon nanostructures

Electromagnetic interference (EMI) can hamper the optimal performance of instruments and even cause damage to the system. One effective solution to this issue is the use of an EMI shield. This study proposes a three-layered heterostructure of a carbon fiber-reinforced polymer (CFRP), WSe₂, and a final cast of multiwall carbon nanotube (MWCNT) as a promising candidate for shielding applications. Samples of different thicknesses of WSe₂ were deposited on CFRP by magnetron sputtering with a pulsed DC source and evaluated for shielding effectiveness. The cast of MWCNT showed an enhanced shielding efficiency compared to the two-layered structure suggesting a potential design for EMI shielding in the automobiles, aviation, and construction industry.   

Timescales for Charge-State Decay of NV- Centers in Diamond

The NV^- color center in diamond has broad application in quantum sensing, computation, and communication. The robustness of the NV^- center, however, is affected by charge-state decay to NV⁰ due to the large hole-capture cross section of optically activated NV^- centers. We present an ab initio formalism for accurately estimating the rate of charge-state decay of color centers in wide-bandgap semiconductors. We employ density functional theory calculations in the context of thermal equilibrium to arrive at our results. The method is illustrated using the transition of NV^- to NV⁰ in the presence of substitutional N [see Z. Yuan et al., PRR 2, 033263 (2020)].   

Title: Passivated Interfacial Traps of Monolayer Phototransistor [P1] with Bipolar Electrical Pulse

   Heterogeneous integration of monolayer semiconductors is an emergent approach to induce unprecedented properties. A long-standing challenge along this route is to manipulate the interfacial configurations of each unit in stacking architecture.Monolayer of transition metal dichalcogenides (TMDs) offers an embodiment of studying interface engineering of integrated systems because optoelectronic performances generally trade off with each other due to interfacial trap states. [1-3]

   By utilizing a bipolar gate pulse, electrostatic passivation of interfacial traps is accomplished. These findings open pathways for the development of integrated devices of the stacked monolayers.

Ref 

[1] Chen, P.-H.; Chen, C.-A.; Lin, Y.-T.; Hsieh, P.-Y.; Chuang, M.-H.; Liu, X.; Hsieh, T.-Y.; Shen, C.-H.; Shieh, J.-M.; Wu, M.-C. Passivated Interfacial Traps of Monolayer MoS2 with Bipolar Electrical Pulse. ACS Applied Materials & Interfaces 2023, 15 (8), 10812-10819.

[2] Hu, Z.; Wu, Z.; Han, C.; He, J.; Ni, Z.; Chen, W. Two-Dimensional Transition Metal Dichalcogenides: Interface and Defect Engineering. Chem. Soc. Rev. 2018, 47, 3100−3128.

[3] Cao, G.; An, Y.; Bao, Q.; Li, X. Physics and Optoelectronic Simulation of Photodetectors Based on 2D Materials. Adv. Opt. Mater. 2019, 7, No. 1900410.   

Development of 2D Semiconductor Oxide Based on β-TeO2 with Room Temperature Broad Photoluminescence

2D oxide semiconductors with large band-gap have gained significant attention for the development of high-performance and energy-efficient electronics. Recently, there have been few theoretical investigations on β-phase TeO₂. Moreover, only a handful of experimental work has been demonstrated, which shows β-TeO₂ transistors exhibit a high-mobility p-type semiconductor with hole mobility up to ~232 cm² V^-1 s^-1 at room temperature and a band gap in the range of 3.2 to 3.7 for bulk to monolayer, respectively. Here, we report a reliable and well-controlled method to form layered β-TeO₂ large band gap semiconductor obtained via deterministic laser-induced oxidation of exfoliated β-Te. We show Raman signatures of β-TeO₂ readily after laser oxidation. This 2D wide bandgap semiconductor possesses a broad photoluminescence (PL) spectrum with multiple peaks covering the range 1.76 eV to 2.08 eV. This optical emission indicates a strong exciton binding energy which is estimated to reach ~1.54 eV to 1.6 eV. This work highlights important methods to obtain 2D oxide semiconductor with large band gap for electronic and photonic applications.   

Guest-induced phase transition leads to polarization enhancement in MHyPbCl3

Hybrid perovskites offer more structural and chemical flexibility than traditional metal halide perovskites. In supertolerant 3D perovskites, a strong organic-inorganic sublattice coupling can influence several physical properties significantly. Here, we use first-principles calculations to explore the structural and polar properties of one such member, methylhydrazinium lead chloride, MHyPbCl₃, as it transitions from highly polar Phase-I to less polar Phase-II upon cooling. From a host/guest perspective, the two phases vary structurally in the guest (MHy) orientation and the two differently distorted host (lead halide) layers. Unlike most hybrid perovskites, this transition is primarily driven by the guest reorientation, further confirmed by a minimum energy path calculation. Maximally localized Wannier functions identify the atomistic origin of polarization enhancement as the host atoms, especially the more distorted octahedral layer. The guest, despite being the primary order parameter for transition, has a negligible contribution, in contrast to prior suggestions. The host distortion also induces significant feedback polarization on the guest molecule, which alters the density of states occupied by the guest at the band edge, leading to a nontrivial impact of the guest on optoelectronic properties.   

High-field photocarrier dynamics in multilayer WSe2 driven by intense terahertz fields

We investigate high-field photocarrier dynamics in a 2D semiconductor, WSe₂, employing time-resolved nonlinear THz spectroscopy. Non-equilibrium photocarriers in multilayer WSe₂ injected by femtosecond laser pulses exhibit extraordinary nonlinear dynamics in the presence of intense THz fields. THz absorption in optically excited WSe₂ rises rapidly in the low THz field regime and more gradually ramps up at high intensities. The nonlinear THz absorption in WSe₂ is extraordinary, since intense THz pulses enhance transparency in conventional 3D semiconductors such as Si, Ge and GaAs as well as another 2D material, graphene. The spectrally analyzed nonlinear THz absorption provides insights into the underlying microscopic processes of the high-field photocarrier dynamics in WSe₂. The permittivity spectrum of the optically excited WSe₂ is predominantly imaginary and inversely proportional to the frequency at low frequencies, which is consistent with the THz properties of conducting media. The conductivity spectrum, however, shows prominent spectral features, implying that the photocarriers undergo resonant interactions such as carrier-phonon scattering. The high-speed control of the electronic structure of 2D semiconductors via THz fields can provide promising platforms not only for nanoelectronic and spintronic applications, but also for exploring fundamental physical processes such as phase transitions and many-body interactions.