Bandgap Energy Control Research Articles

Bandgap energy controlling and electrochemical performances of quaternary metal oxide combined graphene-TiO2 nanocomposite and its photocatalytic hydrogen evolution

A quaternary metal oxide (BiZnSb2O4) combined graphene-TiO2 nanocomposite could be used to control band gap energy using a heterojunction for high hydrogen production by photocatalytic activity. Here, we designed a BiZnSb2O4 combined graphene-TiO2 heterostructure using a high-power sonic synthesis process. The photocatalyst prepared in this way was coated on a nickel foam in the form of a thin film. Various techniques were then used to characterize the nanoscale composite hybrid. Standard three-probe electrode systems were used for cyclic voltammetry test, LSV, and Tafel data. Finally, we obtained good hydrogen evolution results using three different types of nanocomposites with bandgap energy control. To check photoreaction characteristics of the synthesized sample, more current generation reactions were confirmed in the photocatalyst because light existed in the evaluation of electrochemical characteristics depending on the presence or absence of light. Among these three samples, the BZSB-G-T photocatalyst showed the highest hydrogen production amount (95.5 μmol/g without ultrasonic and 112.6 μmol/g with ultrasonic during 4 h). In addition, BZSB-G-T had a lower band-value energy effect with a heterojunction effect compared to the other two types of photocatalysts owing to its synergetic effects.

Bandgap energy controlling of quaternary metal sulfide-graphene-ZnO ternary nanocomposite for photocatalytic reduction of CO2

Graphene-based semiconductor materials are commonly used in CO2 reduction experiments to provide stability against climate change and energy crises. The lack of charge separation, insufficient active area, and unsuccessful junctions are deficiencies in poor semiconductor materials. This study addresses these deficiencies by designing a ternary nanomaterial structure containing a quaternary chalcogenide nanocomposite for bandgap energy control. Alpha-hydroxide carboxylic acids have been used to synthesize quaternary chalcogenides. Its primary function is to form a chain by inducing transition metal interactions. The AgFeNi2S4-Graphene-ZnO ternary photocatalyst was synthesized using a modified solvothermal method and used for the photoreduction of CO2. The photoreduction of CO2 was conducted under various conditions, such as different light sources (λ = 254 and 565 nm), using two types of electron donors to increase the diffusion of CO2 and prolong the decay time of surface electrons. The hybrid AgFeNi2S4-Graphene-ZnO photocatalyst showed high levels of CO2 reduction to methanol because of the improved charge transfer between graphene, ZnO, and quaternary chalcogenide nanocomposites with successful interconnection. The stability and recyclability of the photocatalysts were determined after six-times recycling tests. This study offers a promising strategy for reducing CO2 emissions and creating a high-capacity catalyst for the production of hydrocarbon fuels.

Efficient control of band gap energy and optical properties of titania thin films for solar cell applications

Titanium dioxide, also known as titania is an important semiconducting oxide that has gained prominence in recent years for applications in photoelectrochemical/dye-sensitized solar cells. TiO2 is at present preferred over oxides such as ZnO or SnO2 for applications in dye-sensitized solar cell, because of its mesoporous structure, which offers high surface area for efficient dye loading. It is also important that the band gap of the metal oxide can be adjusted for efficient electron injection from most available commercial dyes since the generation of voltage in the device depends mainly on the band edge matching. Herein, TiO2 thin films were deposited in a polyvinyl pyrolidon medium by the chemical bath deposition technique at 65 °C. The inclusion of lead ions during the film formation process led to structural modification of the thin films of titania – anatase (TiO2) and subsequent formation of structurally disordered Pb-doped TiO2 thin films. The resulting films retain the high band gap energy of crystalline anatase and substantially tuned in the range, 2.85–3.26 ± 0.05 eV by the Pb2+ inclusion.

Bandgap engineering in semiconductor alloy nanomaterials with widely tunable compositions

Over the past decade, tremendous progress has been achieved in the development of nanoscale semiconductor materials with a wide range of bandgaps by alloying different individual semiconductors. These materials include traditional II–VI and III–V semiconductors and their alloys, inorganic and hybrid perovskites, and the newly emerging 2D materials. One important common feature of these materials is that their nanoscale dimensions result in a large tolerance to lattice mismatches within a monolithic structure of varying composition or between the substrate and target material, which enables us to achieve almost arbitrary control of the variation of the alloy composition. As a result, the bandgaps of these alloys can be widely tuned without the detrimental defects that are often unavoidable in bulk materials, which have a much more limited tolerance to lattice mismatches. This class of nanomaterials could have a far-reaching impact on a wide range of photonic applications, including tunable lasers, solid-state lighting, artificial photosynthesis and new solar cells. Nanoscale semiconductor materials have large tolerance to lattice mismatches, which enables an almost arbitrary control of alloy composition and bandgap energy. In this Review, semiconductor alloy nanomaterials are examined, and their synthesis, properties and potential for applications — such as lasers, solid-state lighting and solar cells — are discussed.

Control of optical bandgap energy and optical absorption coefficient by geometric parameters in sub-10 nm silicon-nanodisc array structure

A sub-10 nm, high-density, periodic silicon-nanodisc (Si-ND) array has been fabricated using a new top-down process, which involves a 2D array bio-template etching mask made of Listeria-Dps with a 4.5 nm diameter iron oxide core and damage-free neutral-beam etching (Si-ND diameter: 6.4 nm). An Si-ND array with an SiO2 matrix demonstrated more controllable optical bandgap energy due to the fine tunability of the Si-ND thickness and diameter. Unlike the case of shrinking Si-ND thickness, the case of shrinking Si-ND diameter simultaneously increased the optical absorption coefficient and the optical bandgap energy. The optical absorption coefficient became higher due to the decrease in the center-to-center distance of NDs to enhance wavefunction coupling. This means that our 6 nm diameter Si-ND structure can satisfy the strict requirements of optical bandgap energy control and high absorption coefficient for achieving realistic Si quantum dot solar cells.

ペロブスカイト型酸化物La1/3MO3: Pr3+ (M = Nb, Ta)における発光特性 ― バンドギャップとの関係 ―

ペロブスカイト型酸化物La1/3MO3: Pr3+ (M = Nb, Ta)における発光特性 ― バンドギャップとの関係 ―

10 Gbps transmission of electroabsorption modulators integrated with a 4-channel distributed Bragg reflector laser array

10 Gbps data transmission was demonstrated with electroabsorption modulators integrated with a 4-channel wavelength division multiplexing transmitter composed of distributed Bragg reflector (DBR) lasers. A selective area growth technique was employed for the control of bandgap energy in the gain, modulator and passive sections. Then the laser and modulator stripes were fabricated by a buried heterostructure process. The DBR lasers showed uniform threshold currents between 5 and 10 mA, while the slope efficiency was around 0.11 W A−1. By controlling the DBR currents, a 4-channel transmitter was achieved for the channel spacing of 100 GHz (0.8 nm). The electroabsorption modulator showed clear eye openings under 10 Gbps non-return-to-zero modulation. It allowed 10 Gbps error-free operation over a 25 km long single-mode fiber.

Tuning the bandgap of InAs quantum dots by selective-area MOCVD

In-plane bandgap energy control of InAs quantum dots (QDs) grown on GaAs substrates is demonstrated using selective-area epitaxy. Transmission electron microscopy and cathodoluminescence are used for characterization of the selectively grown dots. A single-step growth of a thin InAs quantum well and InAs QDs emitting at 1010 and 1100 nm (at 77 K) on the same wafer is demonstrated. Non-uniform growth profile is reported for the selectively grown QDs in the mask openings. Surface migration of adatoms from higher order facets to (1 0 0) facets results in enhanced deposition rates closer to the edge of the openings and vapour phase diffusion of adatoms results in density variations across the openings over length scales greater than the surface migration length of the adatoms.

Controlling the properties of InGaAs quantum dots by selective-area epitaxy

Selective growth of InGaAs quantum dots on GaAs is reported. It is demonstrated that selective-area epitaxy can be used for in-plane bandgap energy control of quantum dots. Atomic force microscopy and cathodoluminescence are used for characterization of the selectively grown dots. Our results show that the composition, size, and uniformity of dots are determined by the dimensions of the mask used for patterning the substrate. Properties of dots can be selectively tuned by varying the mask dimensions. A single-step growth of a thin InGaAs quantum well and InGaAs quantum dots on the same wafer is demonstrated. By using a single-step growth, dots luminescing at different wavelengths, in the range 1150–1230nm, in different parts of the same wafer are achieved.

Control of chemical composition and band gap energy in Ga In1 − − Al As on InP during molecular beam epitaxy

The growth of Ga x In 1-x-y Al y As, lattice matched with respect to InP, by molecular beam epitaxy (MBE) is investigated. To achieve a precise prediction over the chemical composition, the quaternary layers were produced by the simultaneous growth of the ternaries Ga 0.47 In 0.53 As and Al 0.48 In 0.53 As. The aluminium content y of the quaternary layer is independently preset by the ternary growth rates. The quaternary samples were characterized by X-ray diffraction as well as by low-temperature (4.2 K) and room-temperature (RT) photoluminescence (PL). At both temperatures, we found a linear dependence of the energy at maximum PL intensity on the aluminium content y in the quaternary layer. The calculated linear fit for the quaternary data points corresponds closely with the linear interpolation between our Ga 0.47 In 0.53 As and Al 0.48 In 0.52 As data. These results enabled the determination of the equation system, giving the composition x, y of Ga x In 1-x-y Al y As as a function of the measured lattice mismatch Δd/d and PL.

Large bandgap energy control of [formula omitted] multiple quantum wells selectively grown by low-pressure MOVPE

Bandgap energy control of a selectively grown InAlAsInGaAs multiple quantum well (MQW) on a mask-patterned planar InP substrate was studied in order to expand device applications using the large conduction band offset of 0.5 eV in the InAlAsInGaAs system. The growth mechanism in the InAlAs selective growth was mainly dominated by gas-phase diffusion through the lateral concentration gradient, like that in InGaAs, and distinguishable segregation of highly active Al species was not observed. The induced strain for the grown InAlAs was characterized to achieve a highly crystalline MQW structure. An extremely wide bandgap energy shift exceeding 350 meV was demonstrated for the selectively grown InAlAsInGaAs MQW without polycrystals on the mask.

InAIGaAs selective MOVPE growth with bandgap energy shift

Selective MOVPE of InAlGaAs with almost no polycrystalline growth was achieved. The composition change was also observed in selective InAlGaAs growth. The In content is enhanced with wider mask width, which makes the bandgap energy smaller. A large photoluminescence (PL) peak wavelength shift of 170 nm with a mesa width of 2 /spl mu/m and a mask width of 40 /spl mu/m was achieved. This is the first report on bandgap energy control in InAlGaAs selective growth.

Strained-layer InGaAs-GaAs-AlGaAs buried-heterostructure quantum-well lasers by three-step selective-area metalorganic chemical vapor deposition

Strained-layer In/sub x/Ga/sub 1-x/As-GaAs-Al/sub y/Ga/sub 1-y/As buried-heterostructure (BH) quantum-well lasers have been fabricated using three-step selective area atmospheric pressure metal-organic chemical vapor deposition. Selective-area epitaxy is used to produce BH lasers involving only GaAs on GaAs regrowth, eliminating the detrimental effects associated with exposed Al/sub y/Ga/sub 1-y/As found in other fabrication methods. Additionally, selective-area epitaxy provides inplane bandgap energy control to fabricate BH devices with different wavelengths on the same wafer. Threshold currents as low as 11 mA are obtained for a 540-/spl mu/m-long, 4-/spl mu/m-wide device with uncoated cleaved facets. The devices operate at room temperature to more than 200 mW/uncoated facet with 40% external differential quantum efficiency. In-plane bandgap energy control results in a wide range of possible laser emission wavelengths for BH lasers grown on the same substrate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Selective metalorganic vapor phase epitaxial growth of InGaAsP / InP layers with bandgap energy control in InGaAs / InGaAsP multiple-quantum well structures

Selective metalorganic vapor phase epitaxial growth on a mask-patterned planar InP substrate is studied. For direct applications to active layers and passive waveguide layers in photonic devices, InGaAsP/InP layers are selectively grown on typically 2 μm wide open stripe regions between pairs of SiO 2 mask stripes. For such relatively narrow growth regions, layer thicknesses are enhanced not only by group III species that are laterally diffused in the gas phase, but also by the species that migrate from surfaces of side facets to the top surface. A flat grown surface is obtained by decreasing the amounts of the surface migrated species, which results in an increase of migration lengths on the top surfaces. Selectively grown InGaAs/InGaAsP multiple-quantum well (MQW) ridge structures with crystallographically smooth side facets and flat interfacesare successfully obtained. By changing the mask stripe width, the bandgap energy of the MQW structure is modified. Group III composition change of selectively grown InGaAs layers, which occurs in both of the gas phase diffusion and the surface migration processes, results in an additional bandgap energy shift in thickness-modulated InGaAs quantum wells. A peak wavelength shift as large as 200 nm is obtained from photoluminescence spectra of simultaneously grown MQW ridge structures, while maintaining flat interfaces.

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-extinction-ratio MQW electroabsorption-modulator integrated DFB laser fabricated by in-plane bandgap energy control technique

The local bandgap energy of an InGaAs/InGaAsP multiple quantum well (MQW) structure was precisely adjusted by in-plane Eg control in one-step selective area metalorganic chemical vapor deposition (MOCVD) growth. The technique was then applied to an MQW electroabsorption-modulator integrated distributed feedback (DFB) laser. Experimental results showed superior device characteristics, such as a high extinction ratio of 25 dB and low threshold current of 15 mA. >

High-speed (10 Gbit/s) and low-drive-voltage (1 V peak to peak) InGaAs/InGaAsP MQW electroabsorption-modulator integrated DFB laser with semi-insulating buried heterostructure

An MQW electroabsorption-modulator integrated DFB laser fabricated by using the in-plane bandgap energy control technique and a low-capacitance semi-insulating BH process is presented. This device has a threshold current as low as 5.4 mA and a modulation efficiency as high as 13 dB/2V. Modulation at 10 Gbit/s with a modulation voltage of only 1V peak to peak demonstrates the potential value of this device for electroabsorption modulation at 1.55 μm.