Search

Atomic-level prediction combined with machine learning (ML) and density functional theory (DFT) is carried out to accelerate the fast discovery of potential photovoltaics from the 2D perovskites. Based on the ML prediction, stability test, optical absorption, and the theoretical power conversion efficiency (PCE) evaluation, two promising photovoltaics, i.e., Sr2VON3 and Ba2VON3, are discovered with PCE as high as 30.35% and 26.03%, respectively. Cu, Ag, C, N, H, and He ion implantation are adopted to improve the photovoltaic performance of the high-efficiency and best stable perovskite Sr2VON3. The time-dependent DFT electronic stopping calculations for energetic ion implanted Sr2VON3 indicate that the excited electrons from the valence band contribute to the electron–phonon coupling, the evolution and formation of the defects, and the photovoltaic performance. This work opens the way to the high-accuracy fast discovery of the high-efficiency and environmentally stable 2D perovskites solar cells and the further engineering improvement in photovoltaic performance by ion implantation. [ABSTRACT FROM AUTHOR]

Memristive-based electro-optical neuromorphic hardware takes advantage of both the high-density of electronic circuits and the high bandwidth of their photonic counterparts, thus showing potential for low-power artificial intelligence applications. In this Perspective paper, we introduce a class of electro-optical memristors that can emulate the key properties of synapses and neurons, which are essential features for the realization of electro-optical neuromorphic functionalities. We then describe the challenges associated with existing technologies and finally give our viewpoint on possible developments toward an energy-efficient neuromorphic platform. [ABSTRACT FROM AUTHOR]

The nanosize confined effect is believed to contribute to improving the resistance drift in nanophase change devices. However, the smaller dimension of device designs is limited by plane lithography techniques. Phase change memory with a confined thickness of ultrathin GeTe layers is fabricated to overcome the limit of current plane lithography. Those memory cells composed of two-dimensional materials present a suppressed resistance drift in their amorphous phase. The drift exponent ν is reduced to 0.05 for 3 nm GeTe layers. Combined with Raman spectroscopy and ab initio molecular dynamics simulations, the structural relaxation process is described as the decay of tetrahedral-bonded sites. Tetrahedrons in ultrathin films are more stable than those in bulk materials. The local motifs of amorphous GeTe ultrathin films are covalently bonded and highly ordered in a short range. The majority of highly ordered tetrahedral clusters prevents spontaneous structural relaxation and leads to high stability in amorphous states, which helps to stop intrinsic fluctuations in physical properties of SET and RESET states, without an extra processing cost. [ABSTRACT FROM AUTHOR]

(001)-epitaxial (Ba0.5Sr0.5)TiO3 (BST) thin films with different magnitudes of compressive strain were fabricated on SrRuO3/SrTiO3 substrates by pulsed laser deposition, and their electro-optic (EO) properties were characterized by modulation ellipsometry at different temperatures. All fabricated films showed an increased paraelectric-to-ferroelectric phase transition temperature upon compressive strain and revealed c-domain structures in the ferroelectric phase. We experimentally clarified that the EO properties of compressively strained BST thin films are enhanced toward the phase transition temperature modified by the strain. The experimental results were compared with the theoretical prediction based on a phenomenological thermodynamic model. Although the measured EO coefficient r c was less than that theoretically predicted, the experimentally observed strain effect on the EO properties is in good qualitative agreement. [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum-well blue (461±4 nm) light emitting diodes with higher electroluminescence intensity are obtained by postgrowth thermal annealing at 720 °C in O2-ambient. Based on our first-principle total-energy calculations, we conclude that besides dissociating the Mg–H complex by forming H2O, annealing in O2 has another positive effect on the activation of acceptor Mg in GaN. Mg can be further activated by the formation of an impurity band above the valence band maximum of host GaN from the passivated MgGa–ON complex. Our calculated ionization energy for acceptor Mg in the passivated system is about 30 meV shallower than that in pure GaN, in good agreement with previous experimental measurement. Our model can explain that the enhanced electroluminescence intensity of InGaN/GaN MQWs based on Mg-doped p-type GaN is due to a decrease in the ionization energy of Mg acceptor with the presence of oxygen. [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum-well blue (461±4 nm) light emitting diodes with higher electroluminescence intensity are obtained by postgrowth thermal annealing at 720 °C in O2-ambient. Based on our first-principle total-energy calculations, we conclude that besides dissociating the Mg–H complex by forming H2O, annealing in O2 has another positive effect on the activation of acceptor Mg in GaN. Mg can be further activated by the formation of an impurity band above the valence band maximum of host GaN from the passivated MgGa–ON complex. Our calculated ionization energy for acceptor Mg in the passivated system is about 30 meV shallower than that in pure GaN, in good agreement with previous experimental measurement. Our model can explain that the enhanced electroluminescence intensity of InGaN/GaN MQWs based on Mg-doped p-type GaN is due to a decrease in the ionization energy of Mg acceptor with the presence of oxygen. [ABSTRACT FROM AUTHOR]

Green InGaN/GaN multiple quantum wells light-emitting diodes with graded superlattice (GSL) AlGaN/GaN inserting layer are investigated numerically and experimentally. Our simulation results indicate that GSL inserting layer can decrease the effective barrier height of holes by 57 meV, which makes holes more easily inject into the quantum wells. The piezoelectric polarization field near the last barrier is suppressed effectively by introducing of the GSL inserting layer. As a result, the efficiency droop radio is improved from 35.8% to 19.4% at current density of 100 A/cm-2. [ABSTRACT FROM AUTHOR]