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Inhomogeneous gain broadening in InAs/InP quantum dot (QD) lasers has been attributed to non-uniform QD size distribution. In this work, the interaction of two dots and three dots considering inter-dot distance, tilted position, QD size and surface ratio is investigated in terms of probability density function, eigenvalue, confinement potential of electrons and holes, strain distribution and piezoelectric potential for self-assembled InAs/InGaAsP/InP (001) quantum dots grown with double-capping procedure, by using the accurate two-step strain analysis model. It is found that strain distribution, piezoelectric potential and confinement potential are all changed, leading to optical transition energy changed and emission spectrum shifted. It is also discovered that there is greatly reduced probability density of the ground state electrons and holes in small QDs as well as large deviation in spatial overlap between electrons and holes of small QDs in the probability density distribution of the first excited state, when small QDs are overlapped with bigger QDs. Thus, the biggest InAs QD dominates the photoemission when it is closely surrounded by other QDs.

Curbing the growth of global CO2 emissions and limiting global average temperature rise to well below 2 °C are important targets for the international society after the Paris Climate Change Conference. Given the continuously increasing emission trends in most of the developing world, peaking emissions as soon as possible during the developing and transition process is a key challenge in realizing the target globally. In this study, we established a comprehensive analysis framework for peaking stage analysis, based on three scopes accounting, and estimating the impact of in-depth socioeconomic transitions on peaking stages. We further applied it to Beijing, which reversed its growth trend in CO2 emissions and acted as a pioneer in fulfilling the peaking target of emissions during in-depth socioeconomic transition period, in recent years. We found that the turning point for production-based CO2 emissions in Beijing appeared around 2007, which stopped growing and has since been fluctuating around 100 Mt. During the in-depth industrialization process, accelerating the elimination of energy and carbon intensive industries, such as resource-related heavy manufacturing, promoting the transition from industries to services, and upgrading the internal structure of industries, were key factors determining the CO2 emissions peak in Beijing. Meanwhile, the optimization of the internal production structure of consumer and producer services also led to a declining trend of services with the in-depth industrial transition. During the in-depth urbanization process, the reduced CO2 intensity and optimized production structure of shelter and household equipment, and upgraded services dominated consumption structure were the main reasons for urban household CO2 mitigation. Clarifying the mechanism of the CO2 emissions peak during the in-depth socioeconomic transition period in Beijing will help us understand the challenges of peak better and provide valuable references for other countries and regions in the developing world that are facing peaking emissions challenges in the processes of their development.

Rapid economic development in China has resulted in a large amount of carbon dioxide (CO2) emissions in recent years. Hence, how to control the growth of emissions is a great challenge for China. In fact, changes to the industrial structure have played an increasingly significant role in mitigating emissions. However, since different regions in China are in various stages of development, the industrial structure and its impact on emissions vary throughout the country. As one of the first areas that opened up economically, the south coastal economic zone, comprising Guangdong, Fujian, and Hainan provinces, developed with relatively low carbon emissions among the eight economic zones in China. With the aid of a detailed framework based on input-output analysis and structural decomposition analysis, we explored the effects of industrial structure changes on CO2 emissions in this area during 2002–2012. The results show that CO2 emissions experienced slower growth under the influence of industrial structure changes in this area. CO2 emissions from secondary industries in this area were highly concentrated in construction, machinery manufacturing, and light manufacturing, which support the dominant industrial structure. The slower growth rate of CO2 emissions in machinery manufacturing was mainly due to the change in the final demand structure and the improvement of the production structure. Considerable CO2 emissions in construction were avoided by importing carbon-intensive products. Further, CO2 intensity improvement served as an increasingly important factor in reducing CO2 emissions in secondary industries. The tertiary industry played an increasingly significant role in the overall CO2 emissions structure, while its share in the industrial structure continued to decrease during 2002–2012. A number of CO2 emissions that were abated in the tertiary industry resulted from changes to the final demand structure and CO2 intensity improvement in Guangdong and Fujian provinces, but not in Hainan province, indicating greater potential for mitigating CO2 emissions in tertiary sectors of Hainan.

It was found experimentally that growing an ultrathin GaP interlayer/sublayer before InAs quantum dots (QDs) grown on InGaAsP barrier lattice-matched to InP (001) substrates is an efficient way to tune the emission wavelength of InAs/InP QD lasers to 1.55 μm range at room temperature (RT). However, the impact of interlayers/sublayers in InAs/InP QD lasers has not been carefully investigated and analyzed theoretically, and the existing physic model cannot predict the emission wavelength of InAs/InP QD lasers engineered by interlayers/sublayers. In this paper, an improved model, which consists of a three-step strain analysis, is applied to precisely predict measured photoluminescence emissions of various QD samples with the GaP interlayer/sublayer that have a specific thickness or chirped/varied thicknesses at both RT and low temperature. It is found that the impact of the GaP sublayers is to enhance quantum confinement instead to stop As/P exchange. Finally, a new method of emission spectrum blue-shifting and gain spectral bandwidth enhancement of an InAs/InP QD laser is proposed and found to be more efficient. By optimizing sublayer thickness and double capping, a total gain spectral bandwidth of 245.7 nm, as an example, is predicted and peak wavelength is shortened to 1500 nm.

The double-capping procedure has been widely used to control the size distribution of self-assembled InAs/InGaAsP quantum dots during the growth on a (001) InP substrate. However, the conventional simulation method referred to one-step model does not include this procedure, which may lead to inaccuracy in modeling of quantum dots. An accurate method of modeling a single quantum dot including a thorough elastic strain analysis is proposed and developed in this paper. The confinement potential profiles are found significantly different between the two models. A series of settings (i.e., dot heights, dot base sizes, and dot shapes) is considered. The electronic band structure is calculated by using the eight-band $k \cdot p$ model. By comparing with the photoluminescence measurements in previously published works, it is found that the obtained optical transition energies using the accurate two-step model are in better agreement. The bright exciton splitting is found larger in terms of fine structures. Moreover, the impact of the quaternary compositions (arsenic mole fraction) of barrier material is for the first time systematically studied by using this accurate model.

Extensive economic growth brings about tremendous water pollutant discharge, which in turn poses great threats to ecosystem and human health, underscoring the vital importance of coordination between economic development and environment. Meanwhile, with the increasing frequency of commodity flows in China, pollutant leakage and the uneven distribution of economic benefits further enlarge the preexisting economic disparities among regions and trigger regional environmental inequities. Therefore, to understand the status quo of the inequities in China, we calculated the regional environmental inequity index (EI) of thirty provinces in terms of water pollution and value added, and further investigated the flow and important paths across provinces and sectors of water pollution and value added by combining multi–regional input–output analysis and structural path analysis. The results showed that northeastern and part of central and northwestern regions suffered from the most serious environmental inequity, while the eastern and southern coastal provinces benefited the most from interregional trade in 2015. Such inequities were driven by the inconsistent net flows of water pollutants and value added, wherein there was a net transfer of water pollutants from developed regions to less-developed provinces in northeastern and central China; however, value added was generally transferred among developed provinces and from inland less-developed to eastern coastal developed provinces. Thus, economic and environmental benefits were both more common in developed areas. This skewed relationship can be explained by the uneven spatial distribution of key sectors (i.e., agriculture, food and tobacco, construction and hotel and restaurant), that are generally in high water pollution or strongly demand for water polluted intensive products. Thereinto, the primary flowing path is that high water-polluting but low value-added agricultural products produced by inland provinces are processed for foods, ultimately consumed by developed southeastern region. By investigating the environmental inequities that exist and underlying reasons for them in mainland China, our results provide an empirical basis upon which policy makers can promote coordinated and sustainable development among regions in China.

The influence of an ultrathin GaP (or GaAs) sublayer on the nonradiative intraband relaxation in InAs/InGaAsP/InP quantum dots (QDs) is investigated. It is found that, based on our studies, the QDs with some heights (e.g., 1.5 nm) and GaP sublayer thicknesses (e.g., 1.03 monolayers) present the first excited state (ES) with higher state degeneracy with respect to ground state (GS), which suggests that the Auger relaxation is triggered more easily. We also find that the energy difference of the ES and GS decreases with increasing sublayer thickness, which suggests that the electron–phonon interaction is affected. This work further presents a study of intraband relaxation for an InAs/InP QD with a GaP or GaAs sublayer. It is found that there is a critical thickness of the GaP sublayer: When the sublayer is less than the critical thickness, the intraband relaxation is only determined by one-longitudinal optical (LO) phonon or two-LO phonons, which is dependent on QD heights. However, with the GaAs sublayer, QDs do not have the above feature. This finding may be helpful for designing and optimizing high-speed QD devices.

Chinese government committed to peak its CO2 emissions before 2030, while managing its in-depth socioeconomic transition to a slower but more balanced growth. Features of such a transition include rising high-tech manufacturing and services as well as fast-growing household consumption, which both have implications for China’s CO2 emissions peak. In this study, we focus on analyzing the case of Shanghai, a leading city in China, for its experience of realizing CO2 emission stagnation during in-depth socioeconomic transition process. We find that emerging high-tech manufacturing and services in Shanghai, although to some extent having replaced carbon-intensive heavy industries, have generated additional CO2 emissions of respectively 364.7 Mt and 308.6 Mt, mainly through their supply chains during the 2007–2012 time period. We also find that soaring urban household consumption induced huge CO2 emissions, including 251.0 Mt embodied emissions in producing goods and services for urban residents, and additional CO2 emissions associated with massive investment in urban infrastructure and buildings from 2007 to 2012. The challenges we identified from Shanghai’s real case provide useful insights for China to peak its CO2 emissions under its in-depth socioeconomic transition.

China faces a major challenge to support the operation and development of an enormous economy with limited water resources. Decoding the way that the final demand influences water consumption patterns is helpful for understanding the discrepancy between water supply and demand. Especially in the current time, when China has experienced socioeconomic transition and its government has proposed a series of water conservation policies over the years, exploring the transition in the water consumption pattern is necessary for further water conservation in China. Meanwhile, there exist distinct economic levels and stages of development among provinces, making it necessary to develop more refined water management strategies in the various provinces. This study comprehensively investigates the trend, spatial distribution and structure of the water footprint in mainland China. Furthermore, it explores the effects of socioeconomic factors on transitions in water footprint patterns with the aid of multi-regional input–output analysis, structural decomposition analysis, and linear regression. The results show that the water footprints of almost all the provinces were decoupled from economic growth from 2007 to 2012. Several northern provinces dramatically increased their water footprints, further enlarging the difference between north and south. The north also showed a wider urban–rural gap in per capita water footprint than did the south. From the viewpoint of structural transitions, household consumption (as the primary contributor) remained stable while an obvious increase in the water footprint was induced by fixed capital formation, in which agriculture and strategic emerging manufacturing played important roles. From the perspective of driving forces, water intensity improvement and changes in the final demand structure saved water. However, these effects were counteracted by the change in the final demand level and the composition of the final products. By identifying China’s water footprint patterns and its transitions, our results clarify China’s strategic water demand pattern and provide refined insights for future water conservation.

The two-state lasing conditions at room temperature in InAs/InP quantum dot (QD) lasers under a continuous wave electrical bias current are studied. It is found that excited state (ES) lasing is promoted by moderately decreasing spacer thickness and increasing dot-size dispersion in a QD stack, and the physical origins are due to the increased bottleneck effect and inhomogeneous broadening. Moreover, it is proved theoretically that ground state (GS) lasing with high inhomogeneous broadening may result in high phase and intensity noise at a high bias current. Therefore, an appropriate spacer thickness together with appropriate inhomogeneous broadening is critical to the GS and/or ES lasing, which helps an optimal design of laser geometry.

The optical properties of a vertical multilayer stack of semiconductor self-assembled quantum dots (QDs) depend on the coupling status. We present an improved modeling method for analysis of QD stacks, consisting of several separate steps in the elastic strain analysis, to reproduce the realistic unidirectional strain accumulation along the QD growth direction from lower and upper dots. Based on this modeling method, by varying the spacer thickness, we systematically study a large variety of QD stack structures, for better understanding the influence of strain and electronic coupling mechanisms. A “quasi continuum band” or highly degenerate excited state (ES) is found in the closely multi-stacked QDs, probably accounting for the occurrence of distinct blueshifting of the photoluminescence peak wavelength for the decreasing spacer thickness. The enhanced ES emission from this type of stacking QD modeled by using rate equations may pave a way for designing potential high-performance laser devices operating on ES.

Reference [1, Fig. 8] shows the strain-induced band edge modification (−0.65 eV in CB, −0.41 eV in HH, and +0.1 eV in LH, respectively) in the GaP sublayer, and in fact the non-strain band edge plus strain induced band edge modification should be shown. However, this error does not affect the model and conclusion. The corrected Fig. 8 is shown below.