Semiconductor Optoelectronic Devices Research Articles

Photocarrier transport dynamics in lifetime and relaxation regimes of semiconductors

Understanding photogenerated carrier transport dynamics is important for optimizing the performance of various semiconductor optoelectronic devices, such as photocatalysts, solar cells, and radiation detectors. In this paper, the spatiotemporal evolution of photogenerated carriers after excitation is investigated both analytically and numerically, in order to reveal the origin of two contradictory photocarrier motion directions, i.e., separation and ambipolar transport in the semiconductors. An analytical solution of the separation distance between mean positions of photogenerated electrons and holes is derived, which shows that photocarriers will transport ambipolarly in the lifetime regime, where the carrier lifetime τ0 is larger than the dielectric relaxation time τd, and separate spontaneously in the relaxation regime, where τ0<τd. Numerical simulation verifies the analytical results and reveals rich dynamics of carrier transport near the boundary of two regimes. In the lifetime regime, the separation distance rises asymptotically to a polarization distance, while there is a transitional sub-region near the regime boundary where majority carriers go through a separating-ambipolar transformation dynamics. This phenomenon originates from two different components of the drift current. In the relaxation regime, majority carriers deplete because of a larger recombination rate in the minority carrier pulse region. Combining the analytical and numerical results, detailed photocarrier transport dynamics are obtained in the lifetime and relaxation regimes of semiconductors.

Precision Machining of Silicon Substrates

Brittle nonmetallic structural materials, such as quartz, glass, silicon, ceramics, ferrites and glass ceramics, are widely used in mechanical engineering, instrument making and radio electronics, as well as in optical, clock and jewelry industries. These materials have high hardness, strength, wear resistance and brittleness; therefore, their machining is a complicated problem. For production of piezoelectric resonators and filters, semiconductor devices, solid-state lasers, optoelectronic devices and other parts of electronics, plates made from monocrystals of quartz, lithium tantalate and niobate, silicon, germanium, sapphire, etc. are used. Semiconductor plates, which were obtained after cutting of a boule, have a number of defects, such as presence of a mechanically affected layer, nonflateness of sides, twisting and large variation of thickness. Therefore, after cutting it is necessary to carry out grinding and polishing. Grinding (abrasive finishing) is machining of semiconductor plates by means of hard finishing grinding discs (lapping tools) using abrasive flour grains. Finishing discs (lapping tools) are usually made from cast iron, glass, steel, copper or tin. The grain size of flour grains for grinding of semiconductor plates is selected from M14 to M5. Finishing machining of silicon substrates is complicated by a number of factors, such as provision of stable sizes, and, which is more important, the required microrelief of a machined surface, and unacceptability of machining marks and micro fissure on a surface. In Perm National Research Polytechnic University, the method of abrasive finishing and polishing of surfaces of silicon substrates by means of “Rast-350” flat-finishing machine was developed. The feature of the machines is in sliding movement of a tool (lap) along a nonrecurring trajectory, which has a form of a grid of complicated configuration. At that, the speeds of movement of all points of the working face of the lapping tool are the same. The studied and proposed technological recommendations for operations of finishing and polishing of silicon substrates allowed determining the main technological regimes (time, specific pressure, and density of the grid of tool marks), as well as the required abrasive material of corresponding grain size, which allowed providing the required microrelief of substrates (Rz 25 nm, Ra 5 nm) and eliminating machining marks and micro fissures on a polished surface.

Temperature dependence of resonance energy transfer in DCM doped anthracene nanoaggregates

The efficiency of the organic semiconductors in optoelectronic devices is highly dependent upon the excitonic diffusion properties. Again the exciton diffusion properties as well as device performance may be affected by the variation of ambient temperature. Thus it is essential to know the temperature variation effect upon the exciton diffusion properties of an organic semiconductor material. Herein the same understanding has been obtained by observing the energy transfer efficiency in the 2–70 °C temperature range with DCM doped anthracene nanoaggregates. The highly efficient energy transfer process observed in these doped nanoaggregates is established to be diffusion controlled and thus the energy transfer efficiency is directly related to the exciton diffusion property of the host matrix. The present results show significant decrease in energy transfer efficiency upon enhancement in sample temperature. This observation indicates slow exciton diffusion process at higher sample temperature. It contradicts previously reported opposite trend which has been explained by involvement of thermally activated hopping mechanism in organic semiconductor samples. The opposite trend observed here indicate presence of some dominating negative effect in this experimental temperature range. It is proposed that, the temperature dependent enhancement in intermolecular separation as the main possible reason for slower exciton diffusion process and less efficient resonance energy transfer in doped anthracene nanoaggregates.

High-Performance Photocoupler Based on Perovskite Light Emitting Diode and Photodetector.

Photocoupler is a kind of semiconductor optoelectronic device that integrates light-emitting device (LED) and photodetector. It has found wide application in various fields because of its capability to transmit the electrical signal through the conversion of the electricity-light-electricity. Herein, we report the fabrication of a new photocoupler by simply integrating perovskite quantum dots LED and perovskite photodetector on a glass substrate. The as-fabricated photocoupler showed outstanding characteristics with high current transfer ratio (CTR) of 3.35%, which is highly competitive in comparison with other materials based devices. Furthermore, the perovskite photocoupler had a fast response speed of 8 μs/8.26 μs. By further adding an amplification circuit, the CTR could be enhanced by around 50 times to 172.6%. These results indicate that the present perovskite-based photocouplers may find potential application in future integrated circuit and optoelectronic system.

Comparative Analysis of Ni- and Ni0.9Pt0.1-Ge0.9Sn0.1 Solid-State Reaction by Combined Characterizations Methods

GeSn-based alloys present a novel pathway towards the monolithic integration of light sources in mid infrared CMOS-compatible Si photonic circuitry [1]. Semiconductor optoelectronic devices need efficient metallic contacts to receive and deliver power and signal. Ni-stanogermanides (Ni-GeSn) have been proposed as a promising candidate material to reach both low specific contact (Rc) and sheet resistance (Rsh) [2,3] to contact efficiently GeSn-based photonic or electronic devices. However, a low thermal stability of these layers has been evidenced, together with compound agglomeration and segregation [4]. As a solution to these problems Wang et al. showed that the co-sputtering of Ni and Pt extended the thermal stability of the stanogermanides to higher temperatures. Thus leading to a broader window for stanogermanidation and suppressing, to some extent, agglomeration and degradation [4]. In this work, we propose a comparative and comprehensive study of the solid-state reaction of Ni and Ni0.9Pt0.1 films with compressively-strained, 60 nm-thick Ge0.9Sn0.1 layers, epitaxially grown on Ge-buffered Si (100) substrates. Prior to metallization, surface preparation was performed with a 1 min dip in 1% diluted HF sequentially rinsed in deionized water and dried with a N2 gun. Then, 10 nm of Ni or Ni0.9Pt0.1 were deposited by physical vapor deposition and capped with 7 nm of TiN. The Ni and Ni0.9Pt0.1-Ge0.9Sn0.1 phase sequence and crystalline evolution were monitored by in-situ x-ray diffraction (XRD) using an Empyrean PANalytical X-ray diffractometer equipped with a copper (Cu Kα) source, a linear detector (PIXcel1D) and a HTK 1200 Anton Paar furnace working under secondary vacuum. Profiles were acquired from 50 to 600 °C, with 5 °C steps and a scanning time of 7 min per temperature step. The phase analysis was complemented by ex-situ in-plane reciprocal space map with a Rigaku SmartLab X-ray diffractometer. Additionally, samples metallized with the same procedure were ex-situ annealed for 30 s at temperatures ranging from 150 up to 550 °C (with 50 °C steps), in a rapid thermal annealing (RTA) treatment in a N2 environment. The evolution of the surface morphology and the electrical properties were measured by atomic force microscopy (AFM) in Tapping mode with a Bruker FastScan equipment and sheet resistance (Rsh) with a four-point probe meter. AFM and Rsh evidenced that Pt addition improves both morphological and electrical properties of the layers at high temperature. The addition of Pt prevents the surface Root-mean-square (RMS) roughness from increasing with temperature (Figure 1) and postpones morphological surface degradation. Concerning the electrical properties (Figure 2), a plateau where sheet resistance remains stable and low is obtained with Pt addition between 350 and 450 °C. Meanwhile, a sudden increase of Rsh values for Ni-system is observed, this immediately after obtaining the minimum values (9.1 Ω/sq at 350 °C). XRD results for the Ni-Ge0.9Sn0.1 system (Figure 3) reveal a sequential growth in which the first phase appearing corresponds to a Ni-rich phase, i.e. Ni5(Ge0.9Sn0.1)3. Then, at 245 °C, the mono-stanogermanide phase Ni(Ge0.9Sn0.1) is observed; this latter is stable up to 600 °C. The addition of 10 at.% of Pt in Ni thin films (Figure 4) modifies the reaction kinetics, evidenced by the delay in Ni consumption together with a snowplow phenomenon. Additionally, it strongly affects the phase formation sequence promoting PtSnx compound formation and β-Sn segregation as well as a preferential out-of-plane orientation of the mono-stanogermanide phase. Further, the Ni0.9Pt0.1 mono-stanogermanide is unstable and a destabilization of the system is observed to the benefit of the Ni mono-stanogermanide phase, around the 345 – 355 °C temperature range. A summary of the phase formation sequence for both systems is given in Figure 5. The potential impact on device integration of these observations will be discussed. Even though the addition of Pt complicates the solid-state reaction, it was observed that its beneficial impact on surface morphology has an important role for maintaining the integrity of the electrical properties.

Catalyst‐Free, Fast, and Tunable Synthesis for Robust Covalent Polymer Network Semiconducting Thin Films

AbstractCovalent polymer networks (CPNs) are of great technological interest due to their robustness and tunability; however, they are rarely applied as semiconductors in optoelectronic devices due to poor material processability. Herein, a simple, rapid, and powerful approach is reported to prepare CPN thin films based on an in situ thermal azide–alkyne cycloaddition (TAAC) in the absence of catalyst or solvent. The method is demonstrated with perylenediimide and triazine‐based monomers, and affords smooth and homogenous CPN films through solution processing and heat treatment (10 min). Moreover, the site‐specific TAAC realizes semiconducting CPNs without undesired impurities or byproducts, and tunable optoelectronic properties are achieved by varying the reaction temperature, which affects the intermolecular self‐assembly. The obtained CPN films exhibit exceptional solvent resistance and good n‐type semiconducting behavior, which together afford application in a series of multilayer solution‐processed organic photovoltaics, where the presence of CPN films significantly improves the solar energy conversion efficiency to over 8% (7% in control devices) when the CPN is used in a planar‐mixed heterojunction device architecture.

A COMPARATIVE ANALYSIS OF EFFECT OF TEMPERATURE ON BAND-GAP ENERGY OF GALLIUM NITRIDE AND ITS STABILITY BEYOND ROOM TEMPERATURE USING BOSE–EINSTEIN MODEL AND VARSHNI’S MODEL


 High temperature stability of band-gap energy of active layer material of a semiconductor device is one of the major challenges in the field of semiconductor optoelectronic device design. It is essential to ensure the stability in different band-gap energy dependent characteristics of the semiconductor material used to fabricate these devices either directly or indirectly. Different models have been widely used to analyze the band-gap energy dependent characteristics at different temperatures. The most commonly used methods to analyze the temperature dependence of band-gap energy of semiconductor materials are: Passler model, Bose–Einstein model and Varshni’s model. This paper is going to report the limitation of the Bose–Einstein model through a comparative analysis between Bose–Einstein model and Varshni’s model. The numerical analysis is carried out considering GaN as it is one of the most widely used semiconductor materials all over the world. From the numerical results it is ascertained that below the temperature of 95o K both the models show almost same characteristics. However beyond 95o K Varshni’s model shows weaker temperature dependence than that of Bose–Einstein model. Varshni’s model shows that the band-gap energy of GaN at 300o K is found to be 3.43eV, which establishes a good agreement with the theoretically calculated band-gap energy of GaN for operating at room temperature.

Renaissance of an Old Topic: From Borazines to BN-doped Nanographenes.

Graphene is one of the leading materials in today's science, but the lack of a band gap limits its application to replace semiconductors in optoelectronic devices. To overcome this limitation, the replacement of C=C bonds by isostructural and isoelectronic bonds is emerging as an effective strategy to open a band gap in monoatomic graphene layers. First prepared by Stock and Pohland in 1926, borazine is the isoelectronic and isostructural inorganic analogue of benzene, where the C=C bonds are replaced by B-N couples. The strong polarity of the BN bonds widens the molecular HOMO-LUMO gap, imparting strong UV-emission/absorption and electrical insulating properties. These properties make borazine a valuable molecular scaffold to be inserted as doping units in graphitic-based carbon materials to tailor a relevant band gap. It is with this objective that we became interested in the development of new synthetic organic methodologies to gain access to functionalized borazine derivatives. In particular, we have described the synthesis of borazine derivatives that, featuring aryl substituents at the B-centers bearing ortho-functionalities, are exceptionally stable against hydrolysis. Building on these structural motifs, we prepared hybrid BN-doped polyphenylene nanostructures featuring controlled doping patterns, both as dosage and orientation. Finally, exploiting the Friedel-Craft electrophilic aromatic substitution, we could develop the first rational synthesis of the first soluble hexa-peri-hexabenzoborazinocoronene and measured its optoelectronic properties, showing a widening of its gap compared to its full-carbon congener.

Wedge-shaped semiconductor nanowall arrays with excellent light management.

In this Letter, a light management structure composed of wedge-shaped semiconductor nanowall arrays is introduced. Theoretical investigation based on gallium arsenide (GaAs) indicates that a 1000nm high array (wall base width/array periodicity: 500nm) with an effective thickness of only 500nm can deliver a maximum photocurrent density (Jph) of ∼29.0 mA/cm2 at AM1.5G illumination. (For an ideal absorber with the same bandgap, the corresponding value is ∼32.0 mA/cm2.) However, Jph of a 1500nm thick flat GaAs film is only ∼19.2 mA/cm2 at the same illumination condition. The wedge-shaped nanowall arrays meanwhile exhibit good omnidirectional light confinement. At the incident angle of 60°, Jph of the aforementioned nanowall array is ∼12.7 mA/cm2, and the corresponding value for an ideal absorber is ∼16.0 mA/cm2. Considering the simple structure and excellent light confinement in a broad range of the system parameters, including array periodicity, the nanowall height, and the incident angle of light, the wedge-shaped semiconductor nanowall arrays provide a valuable platform for fabricating the related high performance-to-cost semiconductor optoelectronic devices.

Phase stability, mechanical and optoelectronic properties of two novel phases of AlN

Two novel aluminum nitride (which is bct-AlN at ambient pressure, and h-AlN at higher pressure) were predicted using first-principles calculations. The mechanical and phonon dispersion results indicate that bct-AlN is mechanically and dynamically stable at zero pressure, h-AlN phase can be stabilized by increasing pressure and it is mechanically and dynamically stable at 10 GPa. bct-AlN is more favorable than rs-AlN in thermodynamics at ambient pressure. Our calculated band gap of bct-AlN is 5.85 eV. It can be used as semiconductor device and optoelectronic device due to its inherent wide direct band gap. For bct-AlN, the shortest Al–N bond length is 1.8476 Å and its bond order index is 1.28, which shows that strong covalent bonds are formed between Al atoms and N atoms. Moreover, the anisotropy of Young’s modulus and optical properties can be noticed obviously for bct-AlN.

Carrier-phase-estimation algorithm featuring fast trackability for high-speed coherent WDM PON based on RSOA.

There have been substantial efforts to implement high-speed (>10 Gb/s) upstream transmission using reflective semiconductor optical amplifiers (RSOAs) in a coherent wavelength-division-multiplexed (WDM) passive optical network (PON). In such a network, it is necessary to estimate the carrier phase of upstream optical signal to retrieve the phase-modulated information created by RSOA. However, due to the severe waveform distortions caused by the limited modulation bandwidth of RSOA (typically less than 3 GHz), previously reported carrier phase estimation (CPE) algorithms cannot accurately estimate the carrier phase of high-speed quadrature phase-shift keying (QPSK) signal generated from the RSOA seeded by a distributed-feedback (DFB) laser. We propose a novel CPE method capable of tracking the carrier phase rapidly by using a small number of symbols (e.g., 15 symbols) even when the waveforms are severely distorted by the limited modulation bandwidth of RSOA. The proposed CPE method utilizes the linear relationship between the intensity modulation and phase modulation indices inherent in the semiconductor opto-electronic device. By using the proposed method, we demonstrate the transmission of 25.78-Gb/s QPSK signal in a 20-km long loopback fiber link. In this experiment, a commercial DFB laser (linewidth: 3 MHz) is used as the seed light instead of an expensive narrow-linewidth laser. Also shown through the experiment is that the proposed CPE method is highly unsusceptible to variations of parameters required in the proposed method, such as the number of test phases, the accuracy of linewidth enhancement factor, and the accuracy of the normalized amplitude of DC component.

Highly ultraviolet transparent textured indium tin oxide thin films and the application in light emitting diodes

Various kinds of materials have been developed as transparent conductors for applications in semiconductor optoelectronic devices. However, there is a bottleneck that transparent conductive materials lose their transparency at ultraviolet (UV) wavelengths and could not meet the demands for commercial UV device applications. In this work, textured indium tin oxide (ITO) is grown and its potential to be used at UV wavelengths is explored. It is observed that the pronounced Burstein-Moss effect could widen the optical bandgap of the textured ITO to 4.7 eV. The average transmittance in UVA (315 nm–400 nm) and UVB (280 nm–315 nm) ranges is as high as 94% and 74%, respectively. The excellent optical property of textured ITO is attributed to its unique structural property. The compatibility of textured ITO thin films to the device fabrication is demonstrated on 368-nm nitride-based light emitting diodes, and the enhancement of light output power by 14.8% is observed compared to sputtered ITO.

System-Level Thermal Design for LED Automotive Lamp-Based Multiobjective Simulation

The light-emitting diode (LED), a semiconductor optoelectronic device, is increasingly introduced into automotive signaling and lighting applications principally due to its exciting design style and long lifetime. Focusing on automotive contexts, numerous researchers have conducted the thermal optimization concerning structure and material properties in LED automotive lamps to maintain the junction temperature operating within a favorable range. However, these efforts mostly rely on thermal simulations with partly component models and specific boundary conditions, and moreover little temperature tolerance has been given from a whole-lamp-level aspect consisting of the electrical, optical, and mechanical requirements. To qualify the temperature tolerance in the thermal design for LED automotive lamps in in-vehicle environment, in this paper, after a description of the design database, the thermal cost objective function, weighted by the electrical, optical, and mechanical objectives, is defined. Then, the multiphysical 3-D simulation model has been made with whole parts in the LED automotive lamp, calibrated by junction temperatures of the typical modules, and integrated with the built database for a graphic user interface application. Finally the temperature sensitivity analysis based on the integrated platform has been performed to accurately estimate the temperature tolerance of the LED automotive lamp. The suggested methodology and experimental results cast light on balancing between the failure risks and costs in LED automotive lamps in the future cars.

Intrinsic Electronic Structures and Optical Anisotropy of α- and β-Phase Copper Phthalocyanine Molecular Crystals

Electronic structures and optical anisotropy of α- and β-phase copper phthalocyanine (CuPc) molecular crystals have been systemically investigated by first-principles calculations based on Density Functional Theory (DFT). Both crystals were shown to be small gap organic semiconductors with relatively flat and dispersionless bands. The α-CuPc was a direct band gap semiconductor, whereas the β-CuPc was an indirect band gap semiconductor. The analysis of Partial Density of States (PDOS) showed that the top of valance band was mainly contributed by N 2p and C 2p states; the bottom of the conduction band was mainly contributed by N 2p, C 2p and Cu 3d states. The interband optical properties, such as the complex dielectric function, absorption coefficient and complex refractive index, showed a high degree of anisotropy that can be traced to the unique structures of these molecular crystals. The calculated dielectric function for α-CuPc in the low energy region was consistent with the experiment results proposed in the literature. These calculations provided particular interpretations on electronic structure and optical properties of α- and β-CuPc organic semiconductors that were critical to optoelectronics, which would promote the applications of these materials in semiconductor optoelectronic devices.

Cooperative Lamb shift and superradiance in an optoelectronic device

When a single excitation is shared between a large number of two-level systems, a strong enhancement of the spontaneous emission appears. This phenomenon is known as superradiance. This enhanced rate can be accompanied by a shift of the emission frequency, the cooperative Lamb shift, issued from the exchange of virtual photons between the emitters. In this work we present a semiconductor optoelectronic device allowing the observation of these two phenomena at room temperature. We demonstrate experimentally and theoretically that plasma oscillations in spatially separated quantum wells interact through real and virtual photon exchange. This gives rise to a superradiant mode displaying a large cooperative Lamb shift.

The Effect of H‐ and J‐Aggregation on the Photophysical and Photovoltaic Properties of Small Thiophene–Pyridine–DPP Molecules for Bulk‐Heterojunction Solar Cells

The performance of organic semiconductors in optoelectronic devices depends on the functional properties of the individual molecules and their mutual orientations when they are in the solid state. The effect of H‐ and J‐aggregation on the photophysical properties and photovoltaic behavior of four electronically identical but structurally different thiophene–pyridine–diketopyrrolopyrrole molecules is studied. By introducing and changing the position of two hexyl side chains on the two peripheral thiophene units of these molecules, their aggregation in thin films between H‐type and J‐type is effectively tuned, as evidenced from the characteristics of optical absorption, fluorescence, and excited state lifetime. The two derivatives that assemble into J‐type aggregates exhibit a significantly enhanced photovoltaic performance, up to an order of magnitude, compared to the two molecules that form H‐type aggregates. The reasons for this remarkably different behavior are discussed.

Growth and Optical Properties of Direct Band Gap Ge/Ge0.87Sn0.13 Core/Shell Nanowire Arrays

Group IV semiconductor optoelectronic devices are now possible by using strain-free direct band gap GeSn alloys grown on a Ge/Si virtual substrate with Sn contents above 9%. Here, we demonstrate the growth of Ge/GeSn core/shell nanowire arrays with Sn incorporation up to 13% and without the formation of Sn clusters. The nanowire geometry promotes strain relaxation in the Ge0.87Sn0.13 shell and limits the formation of structural defects. This results in room-temperature photoluminescence centered at 0.465 eV and enhanced absorption above 98%. Therefore, direct band gap GeSn grown in a nanowire geometry holds promise as a low-cost and high-efficiency material for photodetectors operating in the short-wave infrared and thermal imaging devices.

Two-Dimensional Semiconductor Optoelectronics Based on van der Waals Heterostructures.

Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDCs) and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW) heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structures of 2D semiconducting TMDCs and their exceptional optical properties, and further discuss the fabrication and distinctive features of vdW heterostructures assembled from different kinds of 2D materials with various physical properties. We then focus on reviewing the recent progress on the fabrication of 2D semiconductor optoelectronic devices based on vdW heterostructures including photodetectors, solar cells, and light-emitting devices. Finally, we highlight the perspectives and challenges of optoelectronics based on 2D semiconductor heterostructures.

Stable monolayer honeycomb-like structures ofRuX2(X=S,Se)

Recent studies show that several metal oxides and dichalcogenides $(M{X}_{2})$, which exist in nature, can be stable in two-dimensional (2D) form and each year several new $M{X}_{2}$ structures are explored. The unstable structures in $H$ (hexagonal) or $T$ (octahedral) forms can be stabilized through Peierls distortion. In this paper, we propose new 2D forms of ${\mathrm{RuS}}_{2}$ and ${\mathrm{RuSe}}_{2}$ materials. We investigate in detail the stability, electronic, magnetic, optical, and thermodynamic properties of 2D $\mathrm{Ru}{X}_{2}$ $(X=\text{S},\text{Se})$ structures from first principles. While their $H$ and $T$ structures are unstable, the distorted $T$ structures $({T}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{Ru}{X}_{2})$ are stable and have a nonmagnetic semiconducting ground state. The molecular dynamic simulations also confirm that ${T}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{Ru}{X}_{2}$ systems are stable even at 500 K without any structural deformation. ${T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{RuS}}_{2}$ and ${T}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{RuSe}}_{2}$ have indirect band gaps with 0.745 eV (1.694 eV with HSE) and 0.798 eV (1.675 eV with HSE) gap values, respectively. We also examine their bilayer and trilayer forms and find direct and smaller band gaps. We find that AA stacking is more favorable than the AB configuration. The new 2D materials obtained can be good candidates with striking properties for applications in semiconductor electronic, optoelectronic devices, and sensor technology.

Field effective band alignment and optical gain in type-I Al0.45Ga0.55As/GaAs0.84P0.16 nano-heterostructures

The energy band alignment at the heterointerfaces plays a vital role in understanding the physics and optical processes such as optical gain or optical absorption in semiconductor opto-electronic devices. This paper reports the behavior of field effective energy band alignment followed by the behavior of probability density of the charge carriers in the respective bands of type-I Al0.45Ga0.55As/GaAs0.84P0.16 symmetric nano-scale-heterostructures. In addition, the optical gain of the structure within TE (transverse electric) and TM (transverse magnetic) modes under constant electric field applied is also simulated and analyzed. In order to simulate the optical gain of the structure, 4×4 diagonal k→.P→ Hamiltonian matrix is solved for the purpose of getting envelope functions associated with carriers, carrier densities, dispersion curves of the quantum well structure, transition matrix elements and finally the optical gain. On behalf of simulated results achieved, it is reported that the optical gain in TM mode is found much greater than that in TE mode which is opposite to usual trends. Moreover, the application of external electric field along the growth direction shows that the optical gain within TM mode and the wavelength both can be controlled by controlling the electric field applied. Thus, the nano-heterostructure can be tuned externally by the application of external electric field within the NIR (near infra red) region.