Theoretical analysis and modelling of degradation for III–V lasers on Si

Abstract: InAs/GaAs quantum-dot (QD) lasers offer a promising method to realise Si-based on-chip light sources. However, the monolithic integration of III–V materials on Si introduces a high density of threading dislocations (TDs), which limits the performance of such a laser device in terms of device lifetime. Here, we proposed a kinetic model including a degradation term and a saturation term to simulate the degradation process caused by the TDs in the early stage of laser operation. By using a rate equation model, the current density in the wetting layer, where the TDs concentrate, is calculated. We compared the rate of degradation of QD lasers with different cavity lengths and of quantum-well lasers, where both are directly grown on Si substrates, by varying the fitting parameters in the calculation of current densities in the kinetic model

Water Quality Prediction in the Luan River Based on 1-DRCNN and BiGRU Hybrid Neural Network Model

The current global water environment has been seriously damaged. The prediction of water quality parameters can provide effective reference materials for future water conditions and water quality improvement. In order to further improve the accuracy of water quality prediction and the stability and generalization ability of the model, we propose a new comprehensive deep learning water quality prediction algorithm. Firstly, the water quality data are cleaned and pretreated by isolation forest, the Lagrange interpolation method, sliding window average, and principal component analysis (PCA). Then, one-dimensional residual convolutional neural networks (1-DRCNN) and bi-directional gated recurrent units (BiGRU) are used to extract the potential local features among water quality parameters and integrate information before and after time series. Finally, a full connection layer is used to obtain the final prediction results of total nitrogen (TN), total phosphorus (TP), and potassium permanganate index (COD-Mn). Our prediction experiment was carried out according to the actual water quality data of Daheiting Reservoir, Luanxian Bridge, and Jianggezhuang at the three control sections of the Luan River in Tangshan City, Hebei Province, from 5 July 2018 to 26 March 2019. The minimum mean absolute percentage error (MAPE) of this method was 2.4866, and the coefficient of determination (R2) was able to reach 0.9431. The experimental results showed that the model proposed in this paper has higher prediction accuracy and generalization than the existing LSTM, GRU, and BiGRU models

Effect of Composition, Interface, and Deposition Sequence on Electrical Properties of Nanolayered Ta2O5-Al2O3 Films Grown on Silicon by Atomic Layer Deposition

Abstracts Nanolayered Ta2O5-Al2O3 composite films were grown on n-type silicon by atomic layer deposition (ALD) within the overlapped ALD window of 220–270 °C. Moreover, post-annealing treatment was carried out to eliminate defects and improve film quality. Nanolayered Ta2O5-Al2O3 composite films remain amorphous after 700 °C annealing. The effects of composition, interface, and deposition sequence on electrical properties of Ta2O5-Al2O3 composite films were investigated in detail utilizing MIS devices. The results demonstrate that the formation of Ta2O5-Al2O3 composite films by mixing Al2O3 into Ta2O5 can decrease the leakage current effectively, but it leads to the decrease of the dielectric constant and the enhancement of the hysteresis effect. The interfaces in composite films are not conducive to prevent the leakage current. The deposition sequence of Si/(Al2O3/Ta2O5)n, Al2O3 as the first covering layer, reduces the leakage current and the hysteresis effect effectively. Therefore, the electrical properties of Ta2O5-Al2O3 composite films could be regulated by adjusting components and structures via ALD to acquire relatively great dielectric constants and acceptable leakage currents

Infrared and Visible Image Fusion Based on Visual Saliency Map and Image Contrast Enhancement

The purpose of infrared and visible image fusion is to generate images with prominent targets and rich information which provides the basis for target detection and recognition. Among the existing image fusion methods, the traditional method is easy to produce artifacts, and the information of the visible target and texture details are not fully preserved, especially for the image fusion under dark scenes and smoke conditions. Therefore, an infrared and visible image fusion method is proposed based on visual saliency image and image contrast enhancement processing. Aiming at the problem that low image contrast brings difficulty to fusion, an improved gamma correction and local mean method is used to enhance the input image contrast. To suppress artifacts that are prone to occur in the process of image fusion, a differential rolling guidance filter (DRGF) method is adopted to decompose the input image into the basic layer and the detail layer. Compared with the traditional multi-scale decomposition method, this method can retain specific edge information and reduce the occurrence of artifacts. In order to solve the problem that the salient object of the fused image is not prominent and the texture detail information is not fully preserved, the salient map extraction method is used to extract the infrared image salient map to guide the fusion image target weight, and on the other hand, it is used to control the fusion weight of the basic layer to improve the shortcomings of the traditional ‘average’ fusion method to weaken the contrast information. In addition, a method based on pixel intensity and gradient is proposed to fuse the detail layer and retain the edge and detail information to the greatest extent. Experimental results show that the proposed method is superior to other fusion algorithms in both subjective and objective aspects

Structure and Dielectric Property of High-k ZrO2 Films Grown by Atomic Layer Deposition Using Tetrakis(Dimethylamido)Zirconium and Ozone

Abstracts High-k metal oxide films are vital for the future development of microelectronics technology. In this work, ZrO2 films were grown on silicon by atomic layer deposition (ALD) using tetrakis(dimethylamido)zirconium and ozone as precursors. The relatively constant deposition rate of 0.125 nm/cycle is obtained within the ALD temperature window of 200–250 °C. The film thickness can be precisely controlled by regulating the number of ALD cycle. The ZrO2 films formed at 200–250 °C have an O/Zr atomic ratio of 1.85–1.9 and a low content of carbon impurity. ZrO2 film begins to crystallize in ALD process above 210 °C, and the crystal structure is changed from cubic and orthorhombic phases to monoclinic and orthorhombic phases with increasing the deposition temperature to 350 °C. Moreover, the effect of annealing temperature on dielectric properties of ZrO2 film was studied utilizing ZrO2-based MIS device. The growth of the interface layer between ZrO2 and Si substrate leads to the decrease in the capacitance and the leakage current of dielectric layer in the MIS device after 1000 °C annealing. ZrO2 film exhibits the relatively high dielectric constant of 32.57 at 100 kHz and the low leakage current density of 3.3 × 10−6 A cm−2 at 1 MV/cm

Analysis on the influence law of traction speed on the cutting performance of coal containing hard concretion

Due to the great differences in mechanical properties between hard concretion and coal, the shearer drum cutting coal and rock containing hard concretion will inevitably lead to a series of problems, such as severe load impact, increased cutting specific energy consumption and low coal loading efficiency. Taking the cutting part of a thin coal seam shearer in service in the target mining area as the prototype, the mechanical models of shearer drum and rocker arm are established by using UG, and the discrete element model of coal wall with hard concretions is built by importing it into EDEM. The influence law of traction speed on coal loading rate, drum load and cutting specific energy consumption is analyzed, and the corresponding fitting relationship function is obtained. Taking the traction speed as the design variable, and the drum load, cutting specific energy consumption and coal loading rate as the comprehensive indicators, a multi-objective optimization function is established. The optimal solution is obtained by using NSGA II optimization algorithm, and the accuracy of the simulation is verified by experiments. This method has certain engineering significance for the reasonable selection of shearer traction speed

Separation Zone Required to Buffer Hazardous Waste Landfills Impact on Scattered Water Supply Sources: From a Whole Lifespan Perspective

Threats from landfill leachate leakage to groundwater quality in remote areas is a major concern globally. Buffering distance (BFD) maintained between landfill site and groundwater supply wells is important to prevent drinking water from contamination of hazardous pollutant. Ignoring the leakage increase in the end of landfill life leads to an underestimate of BFD demand, posing potential threat to drinking safety. This paper constructs a framework for BFD prediction with the consideration of landfill performance degradation by coupling landfill performance evaluation model with the aging and defect evolution model of landfill engineering materials, and carries out model application and verification in a coastal hazardous waste landfill. The results show that during the life cycle of a landfill, its BFD experienced a 1.5-time increase from the start of its operation to its life end and reached 3000 m. Under the condition of landfill performance degradation, the BFDs required to attenuate heavy metals experience more increase than those of organic pollutants; BFD required for zinc (Zn), for example, increases 720 m over the no-degradation condition, while 2,4-dichlorophenol(2,4-D) increases by only 288 m. Considering the uncertainty sourced from model parameter and structure, the BFD should be more than 4050 m to ensure long-term safe drinking under unfavorable conditions such as large amount of leachate, weak degradation and fast diffusion of pollutant in vadose and aquifer. If the BFD cannot meet the demand at the end of the landfill life, the leaching behavior of solid waste can be controlled to reduce it depending on BFD. For example, when the leaching concentration of Cd in the waste is reduced from 0.6 mg/L to 0.17 mg/L, the buffering distance is be reduced from 3000 m to 500 m

Low-temperature solution growth of textured zinc oxide films for light trapping enhancement in thin film silicon solar cells

We study the pyramid-like textured zinc oxide films from low-temperature chemical bath deposition as a promising light trapping component in thin film silicon solar cells. It is found that the surface texture increases as the film thickness increases, while the preferential orientation of the crystal also changes gradually during the film growth. The textured zinc oxide film exhibits high transparency over 80% even for a relatively thick (e.g., 3.5 mu m) film. Numerical modeling further indicates that the short circuit current of the thin film microcrystalline silicon solar cell can be increased by 20% due to the light trapping effect arising from the textured zinc oxide film. Meanwhile, the sheet resistance of the as-grown textured zinc oxide film can be reduced drastically by hydrogen plasma treatment