Unified Hierarchical Relationship Between Thermodynamic Tradeoff Relations

Recent years have witnessed a surge of discoveries in the studies of thermodynamic inequalities: the thermodynamic uncertainty relation (TUR) and the entropic bound (EB) provide a lower bound on the entropy production (EP) in terms of nonequilibrium currents; the classical speed limit (CSL) expresses the lower bound on the EP using the geometry of probability distributions; the power-efficiency (PE) tradeoff dictates the maximum power achievable for a heat engine given the level of its thermal efficiency. In this study, we show that there exists a unified hierarchical structure encompassing all of these bounds, with the fundamental inequality given by a novel extension of the TUR (XTUR) that incorporates the most general range of current-like and state-dependent observables. By selecting more specific observables, the TUR and the EB follow from the XTUR, and the CSL and the PE tradeoff follow from the EB. Our derivations cover both Langevin and Markov jump systems, with the first proof of the EB for the Markov jump systems and a more generalized form of the CSL. We also present concrete examples of the EB for the Markov jump systems and the generalized CSL.Comment: 19 pages, 4 figure

Violet-light spontaneous and stimulated emission from ultrathin In-rich InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

We investigated the spontaneous and stimulated emission properties of violet-light-emitting ultrathin In-rich InGaN/GaN multiple quantum wells (MQWs) with indium content of 60%-70%. The Stokes shift was smaller than that of In-poor InGaN MQWs, and the emission peak position at 3.196 eV was kept constant with increasing pumping power, indicating negligible quantum confined Stark effect in ultrathin In-rich InGaN MQWs despite of high indium content. Optically pumped stimulated emission performed at room temperature was observed at 3.21 eV, the high-energy side of spontaneous emission, when the pumping power density exceeds ???31 kW/ cm2.open6

In-rich InGaN/GaN quantum wells grown by metal-organic chemical vapor deposition

Growth mechanism of In-rich InGaN/GaN quantum wells (QWs) was investigated. First, we examined the initial stage of InN growth on GaN template considering strain-relieving mechanisms such as defect generation, islanding, and alloy formation at 730 degrees C. It was found that, instead of formation of InN layer, defective In-rich InGaN layer with thickness fluctuations was formed to relieve large lattice mismatch over 10% between InN and GaN. By introducing growth interruption (GI) before GaN capping at the same temperature, however, atomically flat InGaN/GaN interfaces were observed, and the quality of In-rich InGaN layer was greatly improved. We found that decomposition and mass transport processes during GI in InGaN layer are responsible for this phenomenon. There exists severe decomposition in InGaN layer during GI, and a 1-nm-thick InGaN layer remained after GI due to stronger bond strength near the InGaN/GaN interface. It was observed that the mass transport processes actively occurred during GI in InGaN layer above 730 degrees C so that defect annihilation in InGaN layer was greatly enhanced. Finally, based on these experimental results, we propose the growth mechanism of In-rich InGaN/GaN QWs using GI.open9

Strong carrier localization and diminished quantum-confined Stark effect in ultra-thin high-indium-content InGaN quantum wells with violet light emission

Here, we report on the optical and structural characteristics of violet-light-emitting, ultra-thin, high-Indium-content (UTHI) InGaN/GaN multiple quantum wells (MQWs), and of conventional low-In-content MQWs, which both emit at similar emission energies though having different well thicknesses and In compositions. The spatial inhomogeneity of In content, and the potential fluctuation in high-efficiency UTHI MQWs were compared to those in the conventional low-In-content MQWs. We conclude that the UTHI InGaN MQWs are a promising structure for achieving better quantum efficiency in the visible and near-ultraviolet spectral range, owing to their strong carrier localization and reduced quantum-confined Stark effect.open0

Observation of oxide precipitates in InN nanostructures

We observed the formation of oxide precipitates (bcc-In(2)O(3)) in InN nanostructures formed during metal-organic chemical vapor deposition (MOCVD) and/or subsequent postgrowth procedures in H(2) ambient. It was found that InN is extremely unstable in H(2) ambient and the activation energy of N(2) desorption of InN is measured to be similar to 0.28 eV, which is one order of magnitude smaller than that of reported value of InN in vacuum. Instability of InN nanostructures under H(2) ambient together with residual oxidant in the reactor facilitates the formation of indium oxide precipitates in the nanostructure matrix during MOCVD or the oxidation of residual indium at the surface, resulting in indium oxide dots.open3

Optical and microstructural studies of atomically flat ultrathin In-rich InGaN/GaN multiple quantum wells

Optical and microstructural properties of atomically flat ultrathin In-rich (UTIR) InGaN/GaN multiple quantum well were investigated by means of photoluminescence (PL), time-resolved PL (TRPL), and cathodoluminescence (CL) experiments. The sample exhibits efficient trapping of the photoexcited carriers into quantum wells (QWs) and the effect of internal electric field in the QWs was found negligible by excitation power-dependent PL and TRPL. These phenomena were attributed to the nature of UTIR InGaN QWs, indicating the potential of this system for application in optoelectronic devices. Variation of TRPL lifetime across the PL band and spatially resolved monochromatic CL mapping images strongly suggest that there is micrometer-scale inhomogeneity in effective band gap in UTIR InGaN/GaN QWs, which is originated from two types of localized areas.open141

The electronic structures of In-Rich InGaN quantum well

We investigated the electronic structures of thin In-rich InGaN quantum well (QW) using an eight-band k center dot p method which includes the effects of strain and piezoelectric field. We compared two different valence band offsets (VBOs) reported in literatures: 0.48 eV and 1.05 eV. Also we investigated the effects of strain relaxation and Indium composition of InGaN layer and proved the accuracy of MEIS result.open1

Compositional analysis of In-rich InGaN layers grown on GaN templates by metalorganic chemical vapor deposition

In-rich InGaN layers were successfully grown on GaN templates by metalorganic chemical vapor deposition. In incorporation in InGaN layer was enhanced by decreasing the growth temperature, and In-rich InGaN layer with In content higher than 70% was obtained below 670 ??C. Especially, double peaks from In-rich InGaN grown at 640 ??C appeared in X-ray diffraction pattern and photoluminescence (PL). The further investigation of strain status of InGaN layers by reciprocal space mapping (RSM) clarified that In-rich InGaN layers were fully relaxed and consisted of InGaN alloys of two different In contents of 82% and 97%, respectively. As a result, we confirmed that compositional inhomogeneity which is mainly reported in Ga-rich InGaN layer could exist in In-rich InGaN layer higher than 80%. We also investigated In incorporation behavior in InGaN at low temperature (640 ??C). In content in InGaN layer was found to be controlled by just changing input gas phase mole fraction (TMIn/(TMGa+TMIn)) at low growth temperature and a linear relationship was observed between In content in InGaN layers and gas phase mole fraction.close141

The impact of substrate surface defects on the properties of two-dimensional van der Waals heterostructures

The recent emergence of vertically stacked van der Waals (vdW) heterostructures provides new opportunities for these materials to be employed in a wide range of novel applications. Understanding the interlayer coupling in the stacking geometries of the heterostructures and its effect on the resultant material properties is particularly important for obtaining materials with desirable properties. Here, we report that the atomic bonding between stacked layers and thereby the interlayer properties of the vdW heterostructures can be well tuned by the substrate surface defects using WS2 flakes directly grown on graphene. We show that the defects of graphene have no significant effect on the crystal structure or the quality of the grown WS2 flakes; however, they have a strong influence on the interlayer interactions between stacked layers, thus affecting the layer deformability, thermal stability, and physical and electrical properties. Our experimental and computational investigations also reveal that WS2 flakes grown on graphene defects form covalent bonds with the underlying graphene via W atomic bridges (i.e., formation of larger overlapping hybrid orbitals), enabling these flakes to exhibit different intrinsic properties, such as higher conductivity and improved contact characteristics than heterostructures that have vdW interactions with graphene. This result emphasizes the importance of understanding the interlayer coupling in the stacking geometries and its correlation effect for designing desirable properties

Electroreflectance and photoluminescence study on InGaN alloys

Photoluminescence (PL) and electroreflectance (ER)measurements on In-rich In xGa 1-xN films grown by using metal-organic chemical vapor deposition at 640 ??C and 670 ??C were performed. Franz-Keldysh Oscillations (FKO's) were observed in the ER spectra. The analysis of the FKO's shows phase separation of InN for the In 0.8Ga 0.2N film, regardless of the growth temperature, whereas in the PL spectrum multiple peaks were resolved only in the sample grown at 640 ??C. This indicates that phase separation exists in this kind of In-rich InGaN alloy independent of the growth temperature. From a deconvolution of the FKO signal in the ER spectra, the bandgap energy of In-rich In xGa 1-xN could be estimated. The dependence of the bandgap energy of the In xGa 1-xN alloy on the In composition (x) was obtained from this information.open2