Photoluminescence analysis of InAIAs-InGaAs HFET Material with Varied Placement of Heavy δ-Doping

Low temperature photoluminescence (PL) has been used to characterize InAlAs/InGaAs/InP heterojunction field-effect transistor (HFET) structure material. A phenomenological lineshape model has been applied to the PL spectrum to derive energy levels and the position of the Fermi-energy and hence the channel carrier concentration. The data is compared with results from low-temperature Hall and Shubnikov-de Hans (SdH) measurements, and fit with a charge-control model of the conduction band. Values for the sheet density are derived from PL for channel-doped structures where SdH measurements are difficult. Changes in the quantum well symmetry through variations in the dopant distribution are shown to be reflected in the PL lineshape.     

Combination of heterojunction and mixed-host structures in one blue fluorescent organic light emitting diode to improve the power efficiency

High power efficiency blue organic light-emitting diode (OLED), based on 2-methyl-9,10-di(2-naphthyl) anthracene (MADN) and p-bis(p-N,N-diphenyl-amino-styryl) benzene (DSA-ph), has been realized by combining heterojunction (HJ) structure and mixed host (MH) structure in one device. This combination resulted in both high current efficiency and low driving voltage, and thus highly efficient blue OLED with peak power efficiency of 5.0 lm/W was achieved, which is approximately five times higher than 1.1 lm/W in the MH control device and 56% higher than 3.2 lm/W in the HJ control device.     

Voltage and current loss in semiconductor solar cells from MCV and simultaneous IV measurements

We present a method for determining the voltage and current loss in solar cells using the modulation capacitance voltage measuring technique. Both losses can be investigated in the forward biased mode and the generator mode. The method is especially suitable for characterising particular loss components due to band offsets and interface recombination in heteroemitter solar cells. Nonlinear loss-versus-current characteristics were generally found for a-Si:H(p⁺), SIPOS(n⁺) and ZnO(n⁺) emitters on c-Si. The losses are strongly modified by the preparation which affects the heterojunction interface. These results can give insight into effects of recombination and band offsets in both bands.     

Solution processable quinacridone based materials as acceptor for organic heterojunction solar cells

Two series of novel quinacridone (QA) based materials that combined a strong absorption over a broad range in visible region with good electrical characteristics, which were used as the new electron-accepting materials for organic solar cells, are explored. Unique cyclic compounds 1-6 are synthesized by incorporating electron withdrawing groups (CN, COOH) at carbonyl position of alkyl substituted quinacridones, which lead to the compounds possessing the characteristics of solution-processed and being suitable for photovoltaic applications. Heterojunction solar cells with simple device configuration using these soluble materials as acceptor and effective donor poly (3-hexyl thiophene) (P3HT) were fabricated. The maximum power conversion efficiency (PCE) achieved in the solar cell based on compound 5 is 0.42% under simulated AM 1.5 solar irradiation with J_sc=1.80 mA cm⁻², V_oc=0.50 V and FF=47%. Although the aimed devices just exhibit moderate PCE, our results clearly suggest that the new-type electron-accepting materials different from fullerene have great potential as acceptor in heterojunction solar cell due to many advantages of the QA derivatives such as relatively inexpensive, good electrochemical stability and could be readily modified.     

Strontuim titanate aided water splitting: An overview of current scenario

Addressing the ever-growing global energy demands and environmental concerns by switching over to sustainable and renewable energy resources have been the thrust area of research in the past few decades. Harnessing the abundant solar energy has been the most viable option in this regard. Perovskites, especially strontium titanate have been among the most explored photocatalytic catalytic systems due to their unique properties. The present review summarises the state of art in the solar assisted water splitting using strontium titanate as catalyst. Strategies adopted in enhancing the visible light sensitivity and performance has been discussed giving emphasis to the mechanistic pathway     

Cooperative effect between BaTiO3 and CaFe2O4 in a cocatalyst-free heterojunction composite for improved photochemical H2 generation

A series of novel BaTiO₃/CaFe₂O₄ heterojunction composites with different weight ratios of CaFe₂O₄ vs BaTiO₃ was successfully fabricated by sonication-calcination method using the pre-prepared BaTiO₃ and CaFe₂O₄ powders synthesized in hydrothermal and sol-gel methods, respectively. The composites were well characterized using XRD, UV–vis DRS, SEM, TEM, EDS and XPS to substantiate that BaTiO₃ and CaFe₂O₄ coexist in the heterojunction composite. The highest photocatalytic hydrogen generation rate was obtained for BaTiO₃/CaFe₂O₄ (40 wt%) compared to either of its individual counterparts and this improvement indicated the existence of a cooperative effect between BaTiO₃ and CaFe₂O₄ in the heterojunction. Based on UV-vis-DRS, photoluminescence and time-resolved fluorescence lifetime measurements, the cooperative effect between BaTiO₃ and CaFe₂O₄ originated from the improved photoresponse in the visible light region and efficient separation of the photogenerated electron–hole pairs augmenting their availability for the photocatalytic reaction. A plausible photocatalytic mechanism was also deduced using electrochemical impedance spectroscopy measurements, describing the migration direction of the separated charge carriers. Moreover, the best composite BaTiO₃/CaFe₂O₄ (40 wt%) exhibited fairly stable photoactivity for H₂ production using the sacrificial agent (Na₂S and Na₂SO₃) without the assistance of any noble metals as cocatalysts.     

Influence of the As/Ga flux ratio on diffusion of Be in MBE GaAs layers

Beryllium (Be) diffusion after rapid thermal annealing experiments is studied in heavily doped GaAs structures grown by MBE. SIMS measurements show that in p/p⁺ structures, Be diffusion is reduced by increasing the As₄/Ga flux ratios. In contrast, no effect is observed in p/p⁺/p structures. Furthermore, Be concentration profiles measured after annealing experiments performed at 770 and 850°C for 30 s indicate that Be redistribution is almost independent of the annealing temperature. These results are discussed in terms of a substitutional interstitial diffusion mechanism.     

Exceptional photocatalytic activity for g-C3N4 activated by H2O2 and integrated with Bi2S3 and Fe3O4 nanoparticles for removal of organic and inorganic pollutants

Herein, hydrogen peroxide activated graphitic carbon nitride (agCN) was combined with Fe₃O₄ and Bi₂S₃ to fabricate agCN/Fe₃O₄/Bi₂S₃ nanocomposites via facile refluxing method, as visible-light-induced photocatalysts for photodegradations of anionic and cationic dyes such as MO, RhB, MB, and photoreduction of Cr(VI). The fabricated samples were explored by XRD, EDX, XPS, TGA, SEM, TEM, HRTEM, VSM, PL, FT-IR, BET, and UV-vis DRS. Photocatalytic activity of the nanocomposite with 20% of Bi₂S₃ was 16.6, 40.4, 19.5, and 12.5 times more than that of the pristine gCN in removal of RhB, MB, MO, and Cr(VI), respectively. A plausible photocatalytic mechanism on the agCN/Fe₃O₄/Bi₂S₃ nanocomposites was proposed by construction of n-n heterojunction between gCN and Bi₂S₃. Also, stability of the magnetic hybrid was characterized through cyclic photocatalytic tests.