Equilibrium Lattice Constant Research Articles

First principle study of structural, electronic, optical and mechanical properties of cubic fluoro-perovskites: (CdXF3, X = Y, Bi)

The full-potential linearized augmented plane wave (FP-LAPW) process is applied for the investigation of structural, mechanical, electronic and including optical properties of cubic perovskites CdXF3 (X = Y, Bi). For the consideration of the exchange–correlation potential, the generalized gradient approximation and the modified Becke–Johnson are implemented. The structural properties, comprising equilibrium lattice constant, the bulk modulus and its pressure derivative are calculated and found that both the compounds are structurally stable in its cubic crystal. Elastic properties including anisotropy factor, elastic constants, Poisson's ratio, shear modulus and Young's modulus are calculated. In elastic properties the higher bulk modulus and B/G ratio yields that these compounds are very hard and ductile in nature. Furthermore, these materials show resistance to plastic deformation ascribed to high value of shear modulus “G.” Calculations of electronic band structure, density of states and electronic charge density indicate that CdYF3 compound has an indirect energy band gap of 2.056 eV from (M-X) while CdBiF3 represents a direct band gap of about 1.027 eV from (M-M). The mixture of ionic and covalent bonding character is found in both CdXF3 (X = Y, Bi) compounds. To investigate and evaluate the contribution of states to the various bands, the full and partial density of states are exploited. Calculations of the optical spectrum like real e1(ω) and imaginary e2(ω) components of dielectric function, optical reflectivity [R(ω)], absorption coefficient [I(ω)], optical conductivity [σ(ω)], refractive index [n(ω)], extinction coefficient and electron energy loss are carried out for the energy range of 0–40 eV. Various transitions between bands were calculated from the imaginary part of the dielectric function. From above examinations, it is deemed that these mixes may include thorough understanding in structuring the prime electronic gadgets. All of the properties are reported for the first time for CdXF3 (X = Y, Bi).

Electronic, structural and optical properties of zincblend and wurtizite cadmium selenide (CdSe) using density functional theory and hubbard correction

Zinc blend (zb) and wurtizite (wz) structure of cadmium selenide (CdSe) is determined using density-functional theory within local density approximation (LDA), generalized gradient approximation (GGA), Hubbard-correction (GGA+U) and Hybrid functional approximation (PBE0 or HSE06). The first principle pseudopotential plane wave is used and the relaxed atomic position for the CdSe in zb and wz structure was obtained by using total energy and force minimization method following the Hellmann Feynman approach. The convergence test of total energy with respect to cutoff energy and k-point sampling is performed . The equilibrium lattice constant and unit cell volume of CdSe in both phases are calculated and the obtained value is compared` with experimental values. In addition the band gap of CdSe is analyzed using DFT within LDA, GGA, DFT+U and PBE0 to approximate the unknown exchange correlation functional. The band gap values obtained using LDA and GGA are severally under estimated due to their poor approximation of exchange-correlation potential. This problem was improved by using projector augmented-wave pseudopotential within Hubbard-correction (GGA+U) and the hybrid functional approximation. Optical properties: complex and real parts of dielectric function, energy loss spectrum and absorption coefficient of CdSe in both ZB and WZ phase were studied.

Structural, electronic, elastic, magnetic, phonon and thermodynamic properties of inverse-Heusler-Ti2FeX (X=Si, Ge, and Sn): Insights from DFT-based computer simulation

The structural, mechanical, electronic and lattice dynamic properties of Ti2FeX (X = Si, Ge, and Sn) inverse-Heusler alloys have been explored via first-principles calculations based on density functional theory. The equilibrium lattice constant, bulk modulus, electronic band structure and magnetic moment values of these alloys have been computed to be consistent with prior studies. Several mechanical parameters such as elastic constants Cij, bulk modulus B, Young modulus E, shear modulus G and Poisson’s ratio υ are calculated, and based on these calculations, mechanical stability is examined. The calculated values of the total magnetic moments are in close agreement with the existing theoretical data and comply with the Slater-Pauling rule. From their calculated electronic band structure, Ti2FeSi, Ti2FeGe and Ti2FeSn are found as half-metallic alloys at the equilibrium lattice constant with a minority-spin energy gap of 0.820, 0.850 and 0.780 eV, respectively. The full phonon spectra, and their total and partial density of states of these alloys have been carried out via the direct method. The calculated phonon spectrum points out dynamic stableness of these alloys. Furthermore, the thermodynamic properties such as the heat capacity, thermal expansion, entropy and Grüneisen parameter have been investigated in the Debye model using the Gibbs2 code with a series of temperature from 0 to 1500 K.

First-principles study of the atomic volume of hydrogen in palladium

The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic parameter of interstitial metal hydrides in which dissociated H occupies interstices in the metal lattice. Such an important property should be able to be reliably calculated by a suitable theory or model in order to explain and understand its origin. In practice, vH is typically obtained by means of ab initio calculations founded on density functional theory (DFT), where the equilibrium lattice constant at zero temperature is found by minimising the Born-Oppenheimer energy. While the absolute lattice constants calculated in this way depend quite strongly on the DFT scheme employed, the present work showed that vH is rather robust against differing calculational approaches, thus making a meaningful comparison of theory and experiment possible. Comparing vH for PdnH (0<n<8) calculated with DFT and obtained from in-situ neutron diffraction measurements revealed a significant discrepancy when octahedral-only interstitial occupancy was assumed. Calculations for PdH with mixed octahedral and tetrahedral occupancy gave a value for vH in agreement with experiment assuming that PdH contains 15–20% tetrahedral H.

Influence of high pressure on mechanical, electronic and thermoelectric transport properties of Tb-filled skutterudite; TbT4P12 (T = Fe, Ru, Os)

The influence of high pressure on mechanical, electronic, and thermoelectric transport properties of TbT4P12 (T = Fe, Ru, Os) have been studied. All the calculations were performed using the full-potential linearized augmented plane wave method, as implemented in the WIEN2k code. The exchange-correlation energy is obtained using generalized gradient approximation due to Perdew-Burke-Ernzerhof for solids. Optimized equilibrium lattice constants of these compounds are in good agreement with the reported experimental values. These compounds are metallic, mechanically stable, but brittle. The values of elastic constants increase with the increase in pressure and become stiffer at high pressure. TbT4P12 (T = Fe, Ru, Os) are suitable for low-temperature thermoelectric applications and among these compounds, TbFe4P12 is most efficient.

Band structure of topological insulator Li(Na)AuS

Half-Heusler semiconductors exhibit similar properties: the differences among their properties lie only in the fact that in ternary compositions the zinc-blende binary substructure does not provide the required 18 electrons, but this is improved by adding an extra transition metal, which restores the electronic balance. Half-Heusler ternary compound with 18 valence electrons under an appropriate uniaxial strain is a topological insulating phase. Most importantly, it is proposed that in the half-Heusler family, the topological insulator should allow the incorporating of superconductivity and magnetism. Using the first-principle full-potential linearized augmented wave method we study the band structure of a series of Li(Na)AuS topological insulators. The electronic and magnetic properties of Heusler alloys are investigated by the WIEN2k package. The exchange-correlations are treated within the generalized gradient approximation of PerdeweBurke and Ernzerhof (GGA), the local spin density approximation (LSDA), by using the modified Becke-Johnson exchange potential and the correlation potential of the local-density approximation (MBJ). Spin-orbit coupling is treated by means of the second variational procedure with the scalar-relativistic calculation as basis. We first determine the equilibrium lattice constants by calculating the total energy. The theoretical lattice constant of LiAuS full-potential GGA is 6.02 Å, which is somewhat greater than the result of pseudopotential(5.99 Å). The calculated equilibrium lattice parameter is 5.86 Å for LSDA. Most of the half-Heusler compounds have band inversion, and open the nature band gaps, but the gap of MBJ is not very good. Smaller uniaxial stress damages the cubic structure and also such a natural band gap of topological insulators. By applying uniaxial tensile stress until the equilibrium position is reached in all directions of the structure, the system band gap value is about 0.2 eV, which is consistent with the result obtained from the band gap of cubic structure equilibrium position. When uniaxial tensile stress is 41%, the system turns into a tetragonal structure, the equilibrium lattice constant is &lt;i&gt;a &lt;/i&gt;= 5.2477 Å and &lt;i&gt;c&lt;/i&gt;/&lt;i&gt;a&lt;/i&gt; = 1.41. We use the method of substitution of homologous elements to ensure the properties of topological insulator of materials without changing the cubic structure, and open the bandgap of materials under the equilibrium lattice constant of the system, thereby improving the feasibility of experimental synthesis of topological insulator materials. Our results for the doping suggest that epitaxial strain encountered during experiment can result in electronic topological transition. We hope that the results presented here conduce to further experimental investigation of the electronic topological transition in half-Heusler compounds.

Магнитострикция в сплавах Fe-=SUB=-75-=/SUB=-Ga-=SUB=-25-x-=/SUB=-Z-=SUB=-x-=/SUB=- (Z=Al, Ge, Si): расчет методом магнитного вращающего момента

This work presents an ab initio study of the effect of a small addition of the third element of III and IV groups on the elastic and magnetoelastic properties of Fe75Ga25 alloy. The dependencies of the tetragonal elastic modulus C', magnetoelastic constant –b1, and the tetragonal magnetostrictive constant λ001 on the concentration of the Z-element in the cubic crystal structures A2 and D03 were obtained with the help of the density functional theory and the magnetic torque method in Fe75Ga25-xZx (Z = Al, Ge, Si) alloys (0≤x≤6 at.%). It is shown that the addition of Al and Si atoms leads to an increase in the tetragonal elastic modulus compared to the Fe75Ga25 binary alloy. A correlation was established in the dependence equilibrium lattice constants a0(x) and λ001(x) in the studied ternary alloys for the A2 structure.

First-principles investigation of half-metallic ferromagnetism of Fe2YSn (Y = Mn, Ti and V) Heusler alloys

In this paper, we use the first-principles calculations based on the density functional theory to investigate structural, electronic and magnetic properties of Fe2YSn with (Y = Mn, Ti and V). The generalized gradient approximation (GGA) method is used for calculations. The Cu2MnAl type structure is energetically more stable than the Hg2CuTi type structure. The negative formation energy is shown as the evidence of thermodynamic stability of the alloy. The calculated total spin moment is found as 3μB and 0μB at the equilibrium lattice constant for Fe2MnSn and Fe2TiSn respectively, which agrees with the Slater-Pauling rule of Mt= Zt-24. The study of electronic and magnetic properties proves that Fe2MnSn and Fe2TiSn full-Heusler alloys are complete half-metallic ferromagnetic materials.

First principle calculations and low cost SLM processing of Ti–TiB composite materials

Abstract In order to obtain low cost, high-performance titanium matrix composite materials, first principle calculations and selective laser melting (SLM) experiments were conducted. Firstly, the properties of several typical reinforcements were compared by first principle calculations method, TiB was chosen as the ideal reinforcement. Secondly, the equilibrium lattice constants, mechanical properties and electronic structure of the titanium matrix and TiB reinforcement were calculated for estimating the properties of the composite materials. Calculation results show that both the elastic constants of Ti and TiB satisfy the mechanical stability conditions, and the bulk modulus, shear modulus, Young's modulus and hardness of TiB are all higher than those of Ti, which meets the reinforcing requirements. On this basis, SLM experiments were conducted to verify the calculations. Low cost, irregularly shaped hydrogenation-dehydrogenation titanium (HDH-Ti) and TiB2 powders were ball milled as the raw materials and printed. Microstructure and mechanical properties of the SLMed Ti–TiB composite materials with different addition content of TiB2 were analyzed, and the associated strengthening mechanism was discussed in detail.

Electronic and Thermoelectric Properties of Li-Based Half-Heusler Alloys: A DFT Study

Abstract In this paper, we have studied the electronic, elastic and thermoelectric properties of the half-Heusler LiCrZ (Z = C, N, Si, and P) materials in Type II phase, in this structure the atomic occupations are X (1/2,1/2,1/2), Y (0,0,0) and Z(1/4,1/4,1/4). The ferromagnetic state of Type II structure was found to be the most stable phase for all studied alloys. After calculating the elastic constants, we found out that the conditions of mechanical stability were verified only for LiCrSi and LiCrP alloys in Type II phase, at both equilibrium a0 and half metallic ahm lattice constants, which indicates that these two compounds can be synthesized experimentally. We should also mention that the half metallic behavior in Type II structure, for LiCrSi and LiCrP compounds, was obtained by straining the equilibrium lattice constants by 2% and 6%, respectively. At ahm, these two systems were identified to be true half metals due to their complete spin polarization and integer value of total magnetic moment. These last ones have reached 3μB per unit cell when Z = Si, and 4μB when Z = P. Using the mean field approximation (MFA), the Curie temperatures of Type II structure were also determined, where the values are estimated to be 456.2 K and 302.8 K, respectively. Finally, the thermoelectric performance has been explored by the classical Boltzmann theory. At low temperatures, the figure of merit has reached 0.73 and 0.93 for LiCrSi and LiCrP, respectively. The considerable ZT values and all calculated physical properties make these two systems promising candidates for thermoelectric applications.

Prediction of mechanical and thermo-physical properties of (Nb-Ti-V-Zr)C high entropy ceramics: A first principles study

Effect of different components on structural, mechanical, thermo-physical properties of (Nb-Ti-V-Zr)C crystalline high entropy ceramics (CHECs) were investigated systematically via performing first principles calculations combined with quasi-harmonic Debye-Grüneisen model. The equilibrium lattice constants and density were evaluated by fitting third-order Birch-Murnaghan equation of state. Based on virtual crystal approximation (VCA) method, elastic moduli and lattice constant were consistent with the results from previous theoretical study and experiments, indicating VCA scheme was suitable for random (Nb-Ti-V-Zr)C CHECs. Then various of thermo-physical properties including volumetric thermal expansion coefficient α, constant volume heat capacity and bulk modulus as a function of temperature were calculated by applying quasi-harmonic Debye-Grüneisen model. In finality, the influence of the concentration of differ rent metallic elements on thermo-physical properties were discussed in detail.

First-principles investigation of electrons’ thermal excitations in UN, UAl2 and ThN

We investigated the electronic heat capacity and energetics of thermal excitations of electrons around Fermi energy of selected metallic compounds (UN, UAl2 and ThN) using first-principles methods. The effect of magnetism was evaluated for UN and UAl2. The generalized gradient approximation (GGA) of the Perdew, Burke, and Ernzerhof functional, developed for solids (/PBEsol) as implemented in Quantum ESPRESSO (QE) was used for UN and UAl2 while the earlier PBE was used for ThN. We found that electrons' thermal excitations would only slightly affect the equilibrium lattice constants in considered compounds except for non-magnetic UN, where it needs to be taken into account. The electron density of states at Fermi energy is larger and therefore an increased effect was found. The calculated electronic heat capacity i predicted to be the largest for non-magnetic UN and very small for non-magnetic ThN. The electronic heat capacity is lower for ferromagnetic UN and UAl2 and larger for all compounds in a non-magnetic state when the lattice constant decreases. Electronic heat capacity increases with temperature and becomes more significant at higher temperatures. The predicted γ coefficients are smaller than the evaluated experimentally at low temperatures, but is in a better agreement with the lower values evaluated at 300 K–1700 K temperature range. Our evaluations of the respective electronic energy correction parameters due to electrons’ thermal excitations show that except for non-magnetic UN, they are at least one order of magnitude smaller than the Grüneisen parameter for ferromagnetic UN, both non-magnetic and ferromagnetic UAl2 and ThN.

First Principle Investigation of Electronic, Transport, and Bulk Properties of Zinc-Blende Magnesium Sulfide

We have studied electronic, structural, and transport properties of zinc-blende magnesium sulfide (zb-MgS). We employed a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) method. Our computational method is able to reach the ground state of a material, as dictated by the second theorem of density functional theory (DFT). Consequently, our findings have the physical content of DFT and agree with available, corresponding experimental ones. The calculated band gap of zb-MgS, a direct gap equal to 4.43 eV, obtained at the experimental lattice constant of 5.620 Å, completely agrees with the experimental band gap of 4.45 ± 0.2 eV. We also report total (DOS) and partial (pDOS) densities of states, electron and hole effective masses, the equilibrium lattice constant, and the bulk modulus. The calculated pDOS also agree with the experiment for the description of the states at the top and the bottom of the valence and conduction bands, respectively.

A DFT investigation of electronic, elastic, and thermal properties of 3d transition metal carbides –TMC (TM = Sc–Zn)

Band structure calculation of electronic, elastic, thermal and electronic properties of 3d Transition metal carbides-TMC (TM = Sc–Zn) have been carried out using full potential linearized augmented plane wave (FP-LAPW) within the framework of density functional theory (DFT) using generalized gradient approximation (GGA) method. The equilibrium lattice constants of 3d TMC (ScC-ZnC) have been obtained by volume optimization. Electronic properties of the compounds such as band structure and density of states (DOS) have been plotted. The elastic constants such as Young’s modulus (E), rigidity modulus (G), bulk modulus (B), Poisson’s ratio (ν), shear anisotropy factor (A) and Lame’s (μ & λ) coefficients have been determined for these compounds (ScC-ZnC) using second order elastic constants (C11, C12, C44). Debye temperature (θD) and Gruneissen parameter for these compounds have been evaluated.

First-principles study of half-metallicity bulk rocksalt structure of CsTe and its surfaces

We report on the calculation of the structural, electronic, magnetic and half-metal properties of the rocksalt CsTe compound using the first principles method which is based on density functional theory. Although this compound does not possess any transitional metal in its formula, it is found to carry the half-metallic ferromagnetic property at bulk as well as the surfaces. The energy gap is equal to 3.32 eV at the equilibrium lattice constant of 7.7 Å. The formation energy is calculated to be -2.91 eV which reveals that this compound is stable. All the above-mentioned properties with the remarkable features open up the possible employment of the investigated material in several applications related to spintronics.

Analysis of structural and electronic properties of NiTiZ (Z = Si, Ge, Sn and Sb) under high-pressure using ab initio calculations

The present study investigates the pressure dependencies of the structural and the thermoelectric properties of the half-Heusler alloys NiTiZ (Z = Si, Ge, Sn and Sb) using the first-principle density functional study. The fully relaxed samples demonstrate a semiconducting characteristic with an increase of the energy-gaps in NiTiZ (Z = Si, Ge and Sn) with pressure whereas the metallic character prevails in NiTiSb throughout the entire range of the pressure considered. The computed equilibrium lattice constants are in excellent agreement with the available experimental and theoretical data. A detailed calculation and analyses of the thermoelectric properties of the above half-Heuslers have been performed. Moreover, among the above half-Heuslers, the dimensionless figure of merit of the semiconducting alloys is maximum for NiTiSn. In case of NiTiGe, we observe a gradual increase in its figure-of-merit value with pressure.

First Principle Study of Structural, Electronic, Elastic, and Magnetic Properties of Half-Heusler Compounds ScTiX (X = Si, Ge, Pb, In, Sb, and Tl)

Herein, we report the study of half-Heusler ScTiX (X = Si, Ge, Pb, In, As, and Tl) compounds for the first time employing the scheme of density functional theory (DFT). The influence of on-site Coulomb interactions is taken into account, and simulations are conducted in generalized gradient approximation with the added Hubbard U term (GGA + U). All the compounds were observed to have a narrow band gap on the spin-down configuration. Though spinning the majority channel (spin-up), it is found to be metallic. Consequently, all compounds are semi-metallic or half-metallic and 100% of spin polarized at the Fermi level. Various features, comprising structural, magnetic, elastic, and electronic properties, are calculated through full-potential linearized augmented plane wave (FP-LAPW) method, since they are incorporated in the computer simulation package of WIEN2k. Equilibrium lattice constants are observed for all the compounds which exist within the domain of 6.4–6.8 A°. The IRelast package is already integrated in WIEN2K that has been used for the elastic properties. Elastic features reflect the brittle character of all the material. The total magnetic moments for all such materials are greater than 3 μB, i.e., 3 μB of MTot. Therefore, the compounds show a strong ferromagnetic behavior. These are therefore expected to be used as shape base for thin layers within metastable situations for spintronic applications. The resulted elastic properties show that ScTiSi is ductile, while all other five compounds represent brittle nature. Above findings delight the prospect of ScTiX (X = Si, Ge, Pb, In, As and Ti) compounds in developing half-metallic HH compounds for spintronics and memory storage appliances.

Strain engineering of electronic structure, phonon, and thermoelectric properties of p-type half-Heusler semiconductor

We thoroughly inspected the strain induced electronic properties, phonon dynamics and thermoelectric performance of ZrRhSb compound via density functional theory calculations. The optimized lattice parameters are in accord with the experimental observations. The equilibrium lattice constant is utilized to predict the p-type semiconducting and indirect energy gap of 1.15 eV between the X and Γ symmetry points. The application of strain widens the band gap up to 1.5 eV at 10% of compressive strain keeping the indirect nature consistent. Phonon studies display positive frequencies up to 5% of expansion and 25% of compression and thus confirm the dynamic stability of ZrRhSb under strain. Machineability and elastic properties, evidenced from elastic constants and Pugh’s parameter characterize it as a ductile alloy while maintaining its Debye temperature to 333 K. Herein, using ab initio quantum mechanical calculations and Boltzmann theory, optimization of thermoelectric performances in strained and robust ZrRhSb phase was performed. Starting from 300 K, it displays satisfactory thermoelectric performances, namely figure of merit ZTe > 0.65 and Seebeck coefficient >190 μV/K. Better performances via strain engineering were obtained at room temperature, where ZTe values reach 0.81 with a minimal fluctuation over broad temperature spectrum. The optimal strain conditions are achieved at 10% compression, where the S = 426 μV/K and figure of merit reaches up to a maximum of 0.91 at 800 K, which signifies the possible exploitation of ZrRhSb for thermoelectric applications.

Computational Study of Structural, Electronic, Elastic, Half-Metallic and Thermoelectric Properties of CoCrScZ (Z=Al, Si, Ge, and Ga) Quaternary Heusler Alloys

The structure, electronic, half-metallic, elastic, and thermoelectric properties of the innovative quaternary Heusler (QH) CoCrScZ (Z=Al, Si, Ge, and Ga) alloys are studied by using density functional theory (DFT). CoCrScZ (Z=Al, Ga, and Ge) materials are found to be magnetically active with 100% spin polarization where partially filled 3d-orbitals of Cr confirm the major contribution to the magnetic moment. The results of half-metallic robustness show that the mechanical stability and half-metallicity of CoCrScZ (Z=Ga and Al) can be well maintained in the range of 5.79 to 6.28 A and 5.84 to 6.33 A, respectively. The QH CoCrScSi has a magnetic moment of 4.0 μB at the equilibrium lattice constant a = 6.04 A. The calculated Cauchy pressure, Pugh, and Poisson ratio prove that all alloys are hard, elastically ductile, and anisotropic. In addition, the temperature-dependent thermoelectric properties have been studied by calculating the electronic thermal conductivity (κ), Seebeck coefficient (S), power factor (PF), and electrical conductivity (σ/τ). High ZT values of 0.15, 0.12, 0.77, and 0.83 were obtained for CoCrScSi, CoCrScGe, CoCrScAl, and CoCrScGa, respectively. Based on our calculations, CoCrScZ (Z=Al, Ge, and Ga) combine both good spintronic and thermoelectric behaviors that may be used in spin injection applications.

First principle studies on the structural, thermodynamic and optoelectronic properties of Boron Bismuth: A promising candidate for mid-infrared optoelectronic applications

A systematic study of the structural, thermodynamic, and optoelectronic properties of zinc blende (ZB) phase Boron Bismuth (BBi)is performed considering the full-potential linearized augmented plane wave (FPLAPW) basis sets based on the density functional theory (DFT) with the Perdew-Burke-Ernzerh of generalized gradient approximation (PBEsol) as exchange correlation (XC) functional and Modified Becke-Johnson (mBJ) potential. Structural optimization yields equilibrium lattice constant of 5.52 Å, bulk modulus of 81 GPa, and elastic stiffness constants. In addition to the fundamental thermodynamic properties and the elastic parameters, the optoelectronic properties such as complete electronic band diagram, electronic density of states (DOS), complex dielectric function, absorption coefficient, refractive index, optical conductivity, energy loss function, extinction coefficient, and reflectivity are evaluated. A smaller value of electronic effective mass as compared to hole effective masses leads to higher electron mobility in BBi which could be beneficial for fabricating electron based devices such as High Electron Mobility Transistors (HEMTs), nMOS, etc. Note that, unlike other B–V semiconductor, BBi exhibits a narrower direct-gap (Γ−Γ) of 422 meV which corresponds to mid-infrared wavelength of ~3 μm. Additionally, wider indirect-gap, and substantial spin orbit-coupling splitting of BBi can prove to be beneficial for fabricating LASERs and Photodetectors with minimal losses.