Direct Band Gap Material Research Articles

Strain and electric field tuning of 2D hexagonal boron arsenide

Group theory and density functional theory (DFT) methods are combined to obtain compact and accurate k · p Hamiltonians that describe the bandstructures around the K and points for the 2D material hexagonal boron arsenide predicted to be an important low-bandgap material for electric, thermoelectric, and piezoelectric properties that supplements the well-studied 2D material hexagonal boron nitride. Hexagonal boron arsenide is a direct bandgap material with band extrema at the K point. The bandgap becomes indirect with a conduction band minimum at the point subject to a strong electric field or biaxial strain. At even higher electric field strengths (approximately 0.75 V Å−1) or a large strain (14%) 2D hexagonal boron arsenide becomes metallic. Our k · p models include to leading orders the influence of strain, electric, and magnetic fields. Excellent qualitative and quantitative agreement between DFT and k · p predictions are demonstrated for different types of strain and electric fields.

Earth-abundant nontoxic direct band gap semiconductors for photovoltaic applications by ab-initio simulations

Direct band gap semiconductors with high optical absorption, high electrical conductivity, high carrier mobility, low reflectance and low recombination rate of charge carriers are needed for a variety of applications in solar energy conversion and optoelectronics. We have identified three ternary semiconductors Ca3PN, NaBaP and ZrOS which have direct-band gap and other promising properties for solar energy applications. The prime novelty of this work mainly projects a detailed information on the electronic structure and optical properties for the three materials. From the first principles computational work and analysis, we have found that all the three materials with optimum band gap (~1.52 eV) value are having suitable absorption coefficient, extinction coefficient, optical conductivity and low reflectance in the visible region. Moreover, these materials are found to have low charge carrier effective masses and low recombination rates which can enhance carrier mobility and electrical conductivity. As a result, we will have three best non-silicon based direct band gap materials consisting of earth-abundant and non-toxic elements in the photovoltaic (PV) industry.

Strain-Engineered Asymmetrical Superlattice Si/Si1–x Ge x Nano-ATT $\langle$ p++-n-n−-n++$\rangle$ Oscillator: Enhanced Photo-Sensitivity in Terahertz Domain

This paper proposes a strained Si-based single drift nano-mixed tunnel avalanche transit time (MITATT) oscillator capable of generating high RF power in the terahertz regime, inaccessible by conventional Si devices. The authors have developed a quantum modified classical drift-diffusion model to study the nanoscale properties of strained Si oscillator. The study reveals that 14.72-GW/m2 RF power could be generated from 0.715-THz strain-engineered Si oscillator. Such performance enhancement of the Si device is due to selective incorporation of trace amounts of Ge in the Si active region. This generates in-plane biaxial strain which in turn degrades the in-plane electron mobility, hence unsuitable for conventional MOSFETs. However, such strain remarkably enhances the out-of-plane mobility, and uniqueness of the current research is the utilization of in-plane strain to boost up the out-of-plane mobility depending on geometry and dimensions of the oscillator’s active region. The model incorporates parasitic series resistance and elevates junction temperature effects on terahertz properties of the device. Incorporation of the strained layer in the active region reduces the parasitic series resistance effect on high frequency properties of the oscillator. Validity of the developed model is established by comparing simulated data with the corresponding experimental observations. The authors have further studied photo irradiation effects on terahertz characteristics of the new class of devices. The structure-induced quantum confinement effect has made the Si-based active region to behave as a partially direct bandgap material, and therefore, a significant improvement is observed in optical sensitivity. To the best of the authors’ knowledge, this is the first report on strain-engineered asymmetrically doped Si/SiGe based avalanche photosensor in the high-frequency terahertz domain.

Epitaxial Ge0.81Sn0.19 Nanowires for Nanoscale Mid-Infrared Emitters.

Highly oriented Ge0.81Sn0.19 nanowires have been synthesized by a low-temperature chemical vapor deposition growth technique. The nanostructures form by a self-seeded vapor-liquid-solid mechanism. In this process, liquid metallic Sn seeds enable the anisotropic crystal growth and act as a sole source of Sn for the formation of the metastable Ge1-xSnx semiconductor material. The strain relaxation for a lattice mismatch of ε = 2.94% between the Ge (111) substrate and the constant Ge0.81Sn0.19 composition of nanowires is confined to a transition zone of <100 nm. In contrast, Ge1-xSnx structures with diameters in the micrometer range show a 5-fold longer compositional gradient very similar to epitaxial thin-film growth. Effects of the Sn growth promoters' dimensions on the morphological and compositional evolution of Ge1-xSnx are described. The temperature- and laser power-dependent photoluminescence analyses verify the formation of a direct band gap material with emission in the mid-infrared region and values expected for unstrained Ge0.81Sn0.19 (e.g., band gap of 0.3 eV at room temperature). These materials hold promise in applications such as thermal imaging and photodetection as well as building blocks for group IV-based mid- to near-IR photonics.

A comparative study of the isoelectronic Cd and Hg substitution in EDTA-capped ZnS nanocrystals

In this research, the surface capped pure ZnS nanoparticles, as well as the Cd- and Hg-doped ones were synthesized via a green ultrasonic-assisted co-precipitation route. The products were characterized by X-ray diffraction, scanning and transmission electron microscopies, Fourier transform infrared, UV–Vis and photoluminescence spectroscopies. The results showed that the synthesized spherical-like nanoparticles are single-phased and well-dispersed with diameters of about 3 nm. They were crystallized in a cubic zincblende structure whose lattice constants increase on doping due to the larger ionic radii of the dopants. The Cd/Hg substitution results in slightly less microstrain and so rather smaller particles. The studied nanoparticles are direct band gap materials whose band gap values vary with Cd/Hg doping from 4.31 eV for ZnS to 3.94/4.40 eV as a result of the competition between the quantum size effect and the composition effect. The effect of the isoelectronic Cd and Hg doping is also revealed as the weakening of the blue photoluminescence band around 430 nm originated from the defect states in ZnS matrix, and the appearance of a red excitonic emission at 640 nm. It was found that in these nanoparticles being smaller than Bohr dimension, the particle size is a determinative parameter for governing the efficiency of the radiative emissions.

First-Principles Study of Electronic Structure and Optical Properties of La-Doped AlN

As a wide-bandgap semiconductor material with small dielectric constant and good thermal stability, aluminium nitride (AlN) can theoretically emit light in the deep ultraviolet wavelength region, so it is important in expanding the response of AlN in the visible region. In order to study the influences of La doping on the photoelectric properties of wurtzite AlN crystal, the first-principle plane-wave pseudopotential method and generalized gradient approximation were used to study the lattice constants, electronic structure and optical properties of undoped and La-doped AlN. The calculation results indicate that the intrinsic AlN is a direct-bandgap semiconductor material which both conduction band bottom and valence band top being at the G point, but La-doped AlN forms an indirect-bandgap semiconductor in which the conduction band bottom is at the G point and the valence band top is at the F point. The peak of the density of states is reduced near Fermi energy, and the electronic localization features are significantly diminished. The La doping makes the forbidden band width of AlN narrow, which reduces the photon energy needed for the electron transition, and shows a red shift phenomenon, which expands the influence on visible light. Therefore, this provides a theoretical basis for the study of the photoelectric properties of rare-earth-metal La-doped AlN.

Effects of volumetric and potential energy change on indirect to direct bandgap transition of Ge/Sn alloy

The germanium-tin (Ge-Sn) alloy has been considered a candidate for applications in Short Wave Infrared optical electronics, because it has the property of transforming pure germanium (Ge), typically an indirect bandgap material, into a direct bandgap material. In this paper, the effects of volumetric and potential energy changes are utilized to calculate how the band structure of the Ge-Sn alloy changes with respect to the fraction of tin (Sn). The results indicate that a transition occurs for a Sn fraction ranging from 5.81% to 8.75% with the alloy lattice-constant bowing parameter that ranges from 0.3 Å to 0.0 Å.

High-pressure characterization of the optical and electronic properties of InVO4, InNbO4, and InTaO4

We have studied the electronic properties at ambient pressure and under high pressure of InVO4, InNbO4, and InTaO4 powders, three candidate materials for hydrogen production by means of photocatalytic water splitting using solar energy. A combination of optical absorption and resistivity measurements and band structure calculations have allowed us to determine that these materials are wide band-gap semiconductors with a band-gap energy of 3.62(5), 3.63(5), and 3.79(5) eV for InVO4, InNbO4, and InTaO4, respectively. The last two compounds are indirect band-gap materials, and InVO4 is a direct band-gap material. The pressure dependence of the band-gap energy and the electrical resistivity have been determined too. In the three compounds, the band gap opens under compression until reaching a critical pressure, where a phase transition occurs. The structural transition triggers a band-gap collapse larger than 1.2 eV in the three materials, being the abrupt decrease in the band-gap energy related to an increase in the pentavalent cation coordination number. The phase transitions also cause changes in the electrical resistivity, which can be correlated with changes induced by pressure in the band structure. An explanation to the reported results is provided based upon ab initio calculations. The conclusions attained are of significance for technological applications of the studied oxides.

Electronic and vibrational properties of van der Waals heterostructures of vertically stacked few-layer atomically thin MoS2 and BP

The state-of-the-art heterostructure-based devices often involve stacks of epilayers of few nanometer thick crystals. However, the ultimate limit would be a hitherto single-atomic-layer structure. Using material-by-design approach, the flexibility of two-dimensional (2D) materials could be explored to develop a multilayered artificial van der Waals (vdW) heterostructure where the synergistic coupling between the individual materials and the underlying interface creates new and novel functionalities. Herein, based on first-principles calculations, we report that vertically stacked few-layer vdW heterostructure of monolayer molybdenum disulfide (MoS2) and hexagonal boron phosphide (BP) is a strong electrically narrow direct bandgap material. More intriguingly, few-layer vdW heterostructure of monolayer MoS2 and BP exhibits superior mechanical properties. In striking contrast to heterostructures of MoS2/graphene, MoS2/WS2, and few-layer graphene, where the 2D moduli are lower than the sum of the 2D modulus of each nanosheet, the mechanical strength of few-layer hybrid vdW heterostructure of monolayer MoS2 and BP rather increased with increasing thickness. We attribute this difference to the unique interlayer and interface coupling, which affected the vibrational properties of the heterostructures including the emergence of shear and breathing phonon modes as well as the transformation of flexural phonon modes. Such superior mechanical properties could be explored for nanoelectromechanical device applications, e.g., as a nanoresonator. We demonstrate that the electronic structure could as well be tuned with both increasing numbers of monolayer stacks and defect-engineering promising for low-power applications.

Inorganic and Hybrid Perovskite Based Laser Devices: A Review.

Inorganic and organic-inorganic (hybrid) perovskite semiconductor materials have attracted worldwide scientific attention and research effort as the new wonder semiconductor material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics, dictate that an excellent direct band gap material for photovoltaic applications must be also an excellent light emitter candidate. This has been realized for the case of perovskite-based light emitting diodes (LEDs) but much less for the case of the respective laser devices. Here, the strides, exclusively in lasing, made since 2014 are presented for the first time. The solution processability, low temperature crystallization, formation of nearly defect free, nanostructures, the long range ambipolar transport, the direct energy band gap, the high spectral emission tunability over the entire visible spectrum and the almost 100% external luminescence efficiency show perovskite semiconductors’ potential to transform the nanophotonics sector. The operational principles, the various adopted material and laser configurations along the future challenges are reviewed and presented in this paper.

ZnO/Silicon-Rich Oxide Superlattices with High Thermoelectric Figure of Merit: A Comprehensive Study by Experiment and Molecular Dynamic Simulation.

ZnO is a direct band gap material that has numerous optoelectronic applications. Recently, the thermoelectric behavior of ZnO has drawn much attention because it is expected to enrich the multifunctional application of ZnO. However, the high thermal conductivity nature of ZnO (∼50 W/(m·K)) is a challenge to further increase its thermoelectrtic figure of merit ( ZT). In this paper, a way to increase the ZT of ZnO thin films by insertion of silicon-rich oxide (SRO) interlayers is reported. All of the constituents are earth-abundant and environmental friendly. The effects of the number of SRO layers, thickness, grain size, heat treatment, and crystallinity of ZnO of the superlattices on the thermoelectric behaviors of ZnO were investigated. The thermoelectric ZT was determined by the transient Harman method by measuring the Seebeck voltage. The thermal conductivity of the ZnO/SRO superlattices that is crucial to elucidate the ZT behaviors is calculated using molecular dynamic simulation, in which the Zn-O and Zn-Zn interactions were described by the Born-Mayer potential and the short-range non-Coulombic O-O interaction was described by the Morse potential. For a given total ZnO/SRO thickness, the grain size of the ZnO decreases monotonically with the increasing number of SRO layers, thus leading to a decrease of the thermal conductivity and an increase of the ZT of the superlattices. As the best result, the annealed 45 nm thick ZnO thin film with three SRO interlayers presents a high ZT of ∼0.16 at room temperature. A comprehensive study on the ZnO/SRO superlattice-based thermoelectrtic devices was carried out by the experiment and theoretical simulation. The results imply potential thermoelectric application of the ZnO/SRO superlattices.

Numerical simulations of two-photon absorption time-resolved photoluminescence to extract the bulk lifetime of semiconductors under varying surface recombination velocities

We investigate the limitations of two-photon absorption time-resolved photoluminescence to measure the low-injection bulk lifetime of different semiconductor materials under varying surface recombination. The excitation source is assumed to be a sub-bandgap pulsed laser and the localized absorption and carrier generation was modeled using a focused TEM00 Gaussian beam under the assumption of diffraction-limited performance. The subsequent carrier kinetics were simulated by applying the finite-difference time-domain method to the continuity equation. Three typical semiconductor materials were modeled: direct bandgap low-mobility material (such as CZTS), direct bandgap high mobility (such as GaAs), and indirect bandgap high mobility (such as float-zone silicon). The extracted effective lifetime as a function of surface recombination velocity was compared to the bulk lifetime and the effective lifetime calculated using an analytical 1D approximation. For the direct bandgap materials, focusing inside the material yields an effective lifetime within a few percent of the bulk lifetime, regardless of the surface recombination velocity, while for excitation close to the surface it is up to 30% lower than the bulk lifetime at high surface recombination velocities (&amp;gt;104 cm/s). For the indirect bandgap material, the effective lifetime is dominated by the surface, making the bulk lifetime inaccessible, even at surface recombination velocities of 100 cm/s. Finally, we use the 1D approximation to find under what conditions the bulk lifetime can be extracted by this method and determine that both the bulk diffusion length and the product of the bulk lifetime and surface recombination velocity must be much less than twice the device thickness.

Synthesis, characterization and photovoltaic applications of noble metal—doped ZnS quantum dots

Un-doped zinc sulphide (ZnS) and noble metal-doped ZnS quantum dots were synthesized by chemical method. The synthesized nanomaterial was characterized by UV-Visible, Fourier Transformed Infra-red Spectrometer (FTIR), Fluorescence, High Resolution Transmission Electron Microscope (HRTEM) and X-ray Diffraction (XRD). Scanning electron microscope complemented with energy dispersive X-ray was used to study particle size and chemical composition of un-doped and metal-doped ZnS QDs. A significant red shift in absorption band was observed in metal doped ZnS sample having concentration of impurity 0.05 M with respect to the un-doped ZnS with increasing the size of nanocrystals. Such red shift of the absorption bands are attributed due to quantum confinement effect. As un-doped and noble metal-doped ZnS QDs are direct band gap materials. The band gap energy of ZnS, Ag-doped, and Au-doped ZnS quantum dots is found to 2.5 eV, 2.4 eV and 2.2 eV, respectively. PL spectrum of the un-doped zinc sulphide nanocrytals witnessed two bands, first at 418 nm and second at 468 nm. However, PL spectrum of Ag-doped ZnS nanocrystals shows no green light emission band while a broad emission ranging up to 700 nm in Au-doped ZnS sample. XRD spectra of synthesized QDs exhibited that the material was in cubic phase. X-ray Photoelectron Spectroscopy (XPS) was used for comparative study of surfaces of zinc sulphide and noble metal zinc sulphide nanocrystals. The effects of inserting ZnS and noble metal doped ZnS nanocrystals in the active layer on the performance of organic solar cells were studied. The active layer mainly comprises of electron acceptor [6,6] phenyl-C61-butyric acid methyl ester (PCBM) and organic electron donor poly (3-hexylthiophene (P3HT) with quantum dots dissolved in dichlorobenzene. The cell conversion efficiency improved by embedding the doped QDs in the active layer blend. The cells fabricated with ZnS QDs exhibited cell conversion efficiency of 1.46%. By doping with silver and gold, the cell conversion efficiency was increased about 1.85% and 2.01%, respectively. The morphology of blend of nanocrystals with P3HT:PCBM were studied using atomic force microscopy.

Structural and optical properties of 2D Ruddlesden‐Popper perovskite (BA)2(FA)n−1PbnI3n+1 compounds for photovoltaic applications

Abstract2D‐3D–structured formamidine perovskite composites are highlighted due to their enhanced stability in solar cell applications. However, the structural and optical properties of 2D formamidine perovskites remain unclear. In this work, we developed new formamidine‐based Ruddlesden‐Popper perovskite compounds (BA)2(FA)n−1PbnI3n+1 (n ≤ 4) using hot‐spin coating. Orthorhombic 2D‐layered perovskites were formed with a mixture of 3D formamidine perovskite from (BA)2(FA)n−1PbnI3n+1 precursors. Their formation highly depended on the solvent used in the precursors, in which dimethyl sulfoxide benefited from the b‐axis oriented growth and improved the crystallization of the compounds. The formamidine‐based Ruddlesden‐Popper perovskites were direct bandgap materials, with the experimental bandgaps of over 1.7 eV, and whose average photoluminescence lifetimes were affected by their chemical components and crystal structures. In addition, planar perovskite solar cells were fabricated by employing these films as absorbing layers. The initial devices from the (BA)2(FA)3Pb4I13 precursors exhibited an efficiency of 2.88% and an open voltage of 0.93 V. These results indicated that the formation and stability of 2D‐structured perovskites were strongly related to the A‐site cations, thus offering new insights into the structures of 2D perovskites and their applications for 2D‐3D–structured perovskite solar cells.

Comparison study of temperature dependent direct/indirect bandgap emissions of Ge1-x-ySixSny and Ge1-ySny grown on Ge buffered Si

Temperature-dependent photoluminescence (PL) of two sets of ternary samples with fixed tin concentrations of ~5.2% (Ge0.924Si0.024Sn0.052, and Ge0.911Si0.036Sn0.053) and ~7.3% (Ge0.900Si0.027Sn0.073, and Ge0.888Si0.04Sn0.072) were measured along with their binary counterparts (Ge0.948Sn0.052 and Ge0.925Sn0.075). The variations of direct bandgap emission (ED) and indirect bandgap emission (EID) with temperature were studied for both ternary and binary alloys by means of Gaussian curve fitting, and the results are compared. The bandgap widths of ternaries clearly increase after Si incorporation into the GeSn with similar Sn concentrations. It is found that for the ternaries both ED and EID peak energies are blue shifted, and the energy separation of ED and EID peaks becomes larger than that of binaries for similar Sn concentrations. Moreover, both ED and EID peaks appear at room temperature (RT) in the GeSiSn spectra, but the ED peak position is greater than EID, indicating these ternaries are indirect bandgap materials. Low temperature PL validates the existence of indirect PL emission in Ge0.90Si0.027Sn0.073 and direct gap behavior in Ge0.925Sn0.075, indicating GeSn becomes a direct bandgap material at lower Sn concentration than GeSiSn. The PL intensities of these ternaries are generally weaker and the spectra become more complicated than those of binaries, probably due to increased strain and defects in the ternaries. Finally, it is found that the effect of large differences in strain of ternary samples on PL peak positions can be greater than that of small Si composition differences in ternaries. A large compressive strain in ternaries can also make splitting of the ED into ED,HH (conduction band minimum-Γ valley to heavy hole maximum) and ED,LH (conduction band minimum-Γ valley to light hole maximum) transitions more observable in the PL spectra.

Band-fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors: a dimensionless joint density of states analysis

We develop a band-fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p-type GaAs and nano-crystalline Ga1-xMnxN, as examples for direct bandgap materials, as well as amorphous Si:Hx, SiC:Hx and SiNx, are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edge.

Electronic structure and luminescent properties of Ce3+-doped Ba3Lu2B6O15, a high-efficient blue-emitting phosphor

A high-efficient blue-emitting phosphor Ba3Lu2B6O15: Ce3+ was synthesized by three-step solid-state method. XRD Rietveld refinement analysis reveals that Ba3Lu2B6O15 is of cubic Ia3(——) system, owning a high-symmetric layer structure with two regular LuO6 octahedrons and one BaO9 polyhedron. Density functional theory (DFT) calculation result indicates BLB is a kind of direct band-gap material with broad band-gap of ~5.10 eV. Ba3Lu2B6O15:Ce3+ phosphor exhibits a bright blue emission under UV excitation with high quantum efficiency of > 90%, and the possible reasons are discussed basing on structural and spectral data. Because of its excellent luminescent properties, Ba3Lu2B6O15:Ce3+ could be a promising candidate as a blue phosphor for NUV LED devices.

The electronic and optical properties of armchair germanene nanoribbons

The electronic and optical properties of armchair germanene nanoribbons (AGeNRs) are studied using the first principles calculations. The band structure, band-gap size, projected density of states (PDOS), and dielectric function of AGeNRs are calculated. Moreover, the variation of these parameters as a function of various ribbon widths is investigated. By increasing the width of ribbons the band-gap size of pristine AGeNRs is decreased according to three different trends. Based on these trends, it is extracted that the AGeNRs can be divided into three categories named as n = 3P, n = 3P+1, n = 3P+2, here n is the number of germanium atoms in the width and P is an integer. Moreover, all these categories are direct band-gap materials and the order of band-gap size is changed as: EG (3P+2) < EG (3P) < EG (3P+1). Due to the direct band-gap size, it can be extracted that all of AGeNR categories are proper for optical applications. Based on the simulation results of this work, it is demonstrated that the AGeNRs are appropriate for optical devices in the range of infrared applications. In addition, the effect of uniaxial tensile and compressive strain on the band-gap size and the dielectric function of AGeNRs is investigated and it is shown that the electronic and optical properties of AGeNRs can be tuned by strain in a wide range.

Comparative Study of ∼2.05 eV Lattice-Matched and Metamorphic (Al)GaInP Solar Cells Grown by MOCVD

This work investigates two conceptually different approaches, both based on the AlGaInP alloy family, to produce metal–organic chemical vapor deposition grown 2.05 eV direct bandgap materials for use in the top cell of AM0 multijunction solar cells. The first approach achieves the target bandgap via (Al0.32Ga0.68) 0.52In0.48P lattice-matched to GaAs. The second approach achieves the target bandgap via relaxed, lattice-mismatched Ga0.66In0.34P. Solar cell characterization and analytical device modeling reveal merits and challenges for both approaches. Both devices are found to possess comparable minority carrier diffusion lengths within the p-type base and an equal bandgap-voltage offset of 0.54 V, suggesting effectively similar base material quality. However, the metamorphic Ga0.66In0.34P cell exhibits a superior quantum efficiency across all wavelengths, particularly at short wavelengths. Modeling results attribute the enhanced short wavelength response to the wider direct bandgap of the internally lattice-matched Al0.69In0.31P window and a longer emitter diffusion length. As such, despite the non-negligible lattice mismatch, the enhanced short wavelength response for the metamorphic Ga0.66In0.34P approach proved significantly advantageous, at least with respect to the growth conditions used in this study. Assuming the use of a perfect antireflection coating, the lower parasitic optical absorption from the wider direct bandgap window alone provides as much as ∼0.72 mA/cm2 additional photocurrent. Combined with the higher quality emitter layer observed in this study, ∼1.1 mA/cm2 additional photocurrent was achieved for the metamorphic Ga0.66In 0.34P approach. These values correspond to ∼3.9% and ∼6.0% of the total available photocurrent for a 2.05 eV bandgap solar cell.

Bandgap Tunability in a One-Dimensional System

The ability to tune the gaps of direct bandgap materials has tremendous potential for applications in the fields of LEDs and solar cells. However, lack of reproducibility of bandgaps due to quantum confinement observed in experiments on reduced dimensional materials, severely affects tunability of their bandgaps. In this article, we report broad theoretical investigations of direct bandgap one-dimensional functionalized isomeric system using their periodic potential profile, where bandgap tunability is demonstrated simply by modifying the potential profile by changing the position of the functional group in a periodic supercell. We found that bandgap in one-dimensional isomeric systems having the same functional group depends upon the width and depth of the deepest potential well at global minimum and derived correlations are verified for known synthetic as well as natural polymers (biological and organic), and also for other one-dimensional direct bandgap systems. This insight would greatly help experimentalists in designing new isomeric systems with different bandgap values for polymers and one-dimensional inorganic systems for possible applications in LEDs and solar cells.