Pressure Dependence Of Band Gap Research Articles

Pressure dependence of band gap of (0 4 0) oriented TlI films

Perfectly (040) oriented Thallium iodide films grown by vacuum thermal evaporation were found to have strain and band gap uncorrelated with their film thicknesses. Band structure of orthorhombic TlI was calculated using Density functional Theory (DFT) with appropriate functional. Elastic constants were calculated for determining the residual stress from strain. Band gaps of films linearly correlate with their residual stress. Experimental stress free direct band gap 2.92 eV determined from band gap-residual stress correlation matches quite closely with calculated 2.88 eV. Pressure coefficient of band gap −1 eV/GPa was determined from the residual stress dependence of band gap.

Pressure-induced band anticrossing in two adamantine ordered-vacancy compounds: CdGa2S4 and HgGa2S4

This paper reports a joint experimental and theoretical study of the electronic band structure of two ordered-vacancy compounds with defect-chalcopyrite structure: CdGa2S4 and HgGa2S4. High-pressure optical-absorption experiments (up to around 17 GPa) combined with first-principles electronic band-structure calculations provide compelling evidence of strong nonlinear pressure dependence of the bandgap in both compounds. The nonlinear pressure dependence is well accounted for by the band anticrossing model that was previously established mostly for selenides with defect chalcopyrite structure. Therefore, our results on two sulfides with defect chalcopyrite structure under compression provide definitive evidence that the nonlinear pressure dependence of the direct bandgap is a common feature of adamantine ordered-vacancy compounds and does not depend on the type of anion.

Structural Electronic and Optical Properties of MgO, CaO and SrO Binary Compounds: Comparison Study

First-principles calculations for electronic and optical properties under pressure effect of MgO, SrO and CaO compounds in the cubic structure, using a full relativistic version of the full-potential augmented plane-wave (FP-LAPW) method based on density functional theory, within the local density approximation (LDA) and the generalized gradient approximation (GGA), have been reported. Furthermore, band structure calculations have been investigated by the alternative form of GGA proposed by Engel and Vosko (GGA-EV) and modified by Becke-Johnson exchange correlation potential (MBJ-GGA). All calculated equilibrium lattices, bulk modulus and band gap at zero pressure are find in good agreement with the available reported data. The pressure dependence of band gap and the static optical dielectric constant are also investigated in this work.

Ultra-sensitive pressure dependence of bandgap of rutile-GeO2 revealed by many body perturbation theory.

The reported values of bandgap of rutile GeO2 calculated by the standard density functional theory within local-density approximation (LDA)/generalized gradient approximation (GGA) show a wide variation (∼2 eV), whose origin remains unresolved. Here, we investigate the reasons for this variation by studying the electronic structure of rutile-GeO2 using many-body perturbation theory within the GW framework. The bandgap as well as valence bandwidth at Γ-point of rutile phase shows a strong dependence on volume change, which is independent of bandgap underestimation problem of LDA/GGA. This strong dependence originates from a change in hybridization among O-p and Ge-(s and p) orbitals. Furthermore, the parabolic nature of first conduction band along X-Γ-M direction changes towards a linear dispersion with volume expansion.

Non-monotonic pressure dependence of band gap in SnTe

The electronic properties of SnTe under pressure are studied using first-principles calculations. The results show that the band gap energy changes non-monotonically with pressure, gradually reducing to zero, then rising. It may be because with pressure the inertia of s state near the bottom of the conduction band is weakened, and the repulsion to p state is enhanced, which pushes the L6+ level down. The work demonstrates an approach for manipulating the electrical properties of SnTe, which is important for future applications based on SnTe.

Low frequency pressure modulation of indium antimonide

A lumped parameter resonator capable of generating megapascal pressures at low frequency (kilohertz) is described. Accelerometers are used to determine the applied pressure, and are calibrated with a piezoelectric sample. A laser diagnostic was also developed to measure the pressure in semiconductor samples through the band gap pressure dependence. In addition, the laser diagnostic has been used to measure the attenuation coefficient α of commercially available indium antimonide (InSb) wafers. The resonator and laser diagnostic have been used with InSb samples to verify the pressure response.

Theoretical study of structural, electronic, and thermal properties of CdS, CdSe and CdTe compounds

A theoretical study of structural, electronic and thermal properties of CdS, CdSe and CdTe compounds is presented; using the full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, both the local density approximation (LDA) and the generalized gradient approximation (GGA) were used for the exchange-correlation potential calculation. The ground-state properties are determined for the bulk materials (CdS, CdSe and CdTe) in cubic phase. Quantities such as the lattice constants and bulk modulus of interest are calculated. Detailed comparisons are made with published experimental and theoretical data and show generally good agreement. Besides this, a numerical first-principles calculation of the elastic constants was used to calculate C11, C12 and C44. The pressure dependence of band gaps for these systems was investigated. We also presented the thermal effects on some macroscopic properties of these compounds using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. We have obtained successfully the variations of the volume, thermal expansion coefficient, heat capacities and Debye temperature as a function of the pressure and temperature.

A theoretical study of band-gap and electrical resistivity of FeS2 (pyrite) at high pressure

The pressure dependence of electrical resistivity of FeS2 (pyrite) has been studied with the help of a simple analytical relation. The calculated results are found in reasonable agreement with the experimental measurements. The computed results are then utilized for the evaluation of pressure dependence of band-gap of FeS2 (pyrite). The obtained results are found to be close to the experimental data. We have also estimated the expected pressure 109.50 GPa for metallization of FeS2 (pyrite), which compares well with the estimated pressure 80(±8) GPa predicted through experiment. The pressure coefficient of logarithm of resistivity and band-gap energy has also been evaluated. Our results are near to the values obtained through the experiment.

Structural, electronic and optical properties of spinel oxides: cadmium gallate and cadmium indate

The structural, electronic and optical properties of two principal representatives of spinel oxides CdGa2O4 and CdIn2O4 have been investigated using the full-potential augmented plane-wave plus local orbitals method within density functional theory. We used the generalized gradient approximation (GGA) for the exchange-correlation (XC) potential. Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for the band structure calculations. The equilibrium lattice constants and the internal parameters are in agreement with the available experimental results. Results obtained for band structure using GGA-EV show a significant improvement over other theoretical work and are closer to the experimental data. The pressure dependence of band gaps is investigated. The dielectric function, reflectivity spectra and refractive index are calculated up to 50 eV. Pressure and volume dependence of the static refractive index have been also calculated.

First-principles studies of pressure dependence of elastic and electronic properties in filled tetrahedral semiconductors LiMgX ( [formula omitted], P, and As)

The elastic and electronic properties of the filled tetrahedral semiconductors LiMgX ( X = N , P, As) under pressure effect have been investigated using the pseudo-potential plane wave method within density functional theory. The equilibrium lattice constant of LiMgX compounds were calculated. A numerical first-principles calculation of the elastic constants was used to calculate C 11 , C 12 , C 44 and their pressure derivatives. Band structure, density of states and pressure dependence of band gaps were investigated. The results are compared with the available theoretical and experimental data.

Elastic, electronic, and lattice dynamical properties of CdS, CdSe, and CdTe

Ab initio calculations, based on norm-conserving pseudopotentials and density functional theory, have been performed to investigate elastic, electronic and lattice dynamical properties of chalcogenides (CdS, CdSe, and CdTe). The calculated lattice parameters, elastic constants, band structures, and phonon dispersions are in good agreement with available experimental and theoretical results. We also presented the pressure-dependence of elastic constants and the pressure-dependence of band gaps.

Electronic structure and structural phase stability of CuAlX2 (X=S, Se, Te) under pressure

The electronic and structural properties of chalcopyrite compounds CuAlX2 (X=S, Se, Te) have been studied using the first principle self-consistent Tight Binding Linear Muffin-Tin Orbital (TBLMTO) method within the local density approximation. The present study deals with the ground state properties, structural phase transition, equations of state and pressure dependence of band gap of CuAlX2 (S, Se, Te) compounds. Electronic structure and hence total energies of these compounds have been computed as a function of reduced volume. The calculated lattice parameters are in good agreement with the available experimental results. At high pressures, structural phase transition from bct structure (chalcopyrite) to cubic structure (rock salt) is observed. The pressure induced structural phase transitions for CuAlS2, CuAlSe2, and CuAlTe2 are observed at 18.01, 14.4 and 8.29 GPa, respectively. Band structures at normal as well as for high-pressure phases have been calculated. The energy band gaps for the above compounds have been calculated as a function of pressure, which indicates the metallic character of these compounds at high-pressure fcc phase. There is a large downshift in band gaps due to hybridatization of the noble-metal d levels with p levels of the other atoms.

Investigation of the pressure dependence of band gaps for silver halides within a first-principles method

The pressure dependence of the direct and indirect band gaps in rocksalt silver halides has been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for the exchange-correlation potential. It is found that indirect band gaps (L→X and L→Γ) exhibit different responses to application of pressure. Similar trends are found for the indirect band gaps of AgCl and AgBr while the trend in AgI (L→Γ) band gap is different. In all the compounds, the effect of pressure on the direct band gaps (Γ→Γ, X→X and L→L) show qualitatively similar results. The fundamental indirect band gap (L→Γ) pressure coefficients are −4.19 meV (GPa) −1 and −3.81 meV (GPa) −1 for AgCl and AgBr while for AgI (L→X) it is −61.50 meV (GPa) −1. The band gap pressure coefficient as well as the volume deformation potential for the various band gaps of the compounds have also been investigated.

Effect of pressure on structural properties and energy band gaps of γ‐InSe

AbstractWe have investigated theoretically the effect of hydrostatic pressure on interatomic bond lengths and energy band gaps of γ‐InSe. Total energy calculations were performed using the linear augmented plane wave (LAPW) method, taking into account scalar relativistic corrections as well as spin‐orbit coupling. Internal structural parameters were optimized for different pressures by adopting as input the unit cell parameters known from experiment. Our theoretical results for the nearest‐neighbor In–Se bond length are in excellent agreement with a recent experimental determination from high‐pressure EXAFS measurements. The covalent In–In bond is found to be more compressible than the partially ionic In–Se bond. We also present the calculated pressure dependence of band gaps and compare to recent high‐pressure experimental studies of optical and transport properties. A large negative pressure coefficient is obtained for the indirect Z–A gap. This leads to a crossover from a direct to an indirect fundamental gap within the stability range of the γ‐polytype of InSe, in qualitative agreement with recent experiments.

Ab initio study of BAs under pressure

AbstractWe use an ab initio total energy pseudopotential technique within the Density Functional Theory in the local‐density approximation to determine the vibrational normal modes (phonons) defined within the first Brillouin Zone of BAs. We also study the effects of hydrostatic pressure on these phonons and the mode Grüneisen parameters using the response‐function formalism for the computation. There is a very good agreement between the transversal optical phonon frequency at the Γ point calculated on this way and that with the frozen phonon technique. We also study the electronic band structure, the band‐gap pressure dependence and the generalized stability criteria.

Pressure Tuning Optical Absorption Spectroscopy of Erbium-Doped Silicon Nanocrystals

High-pressure optical absorption spectroscopic measurements of both erbium-doped and undoped Si nanoparticles have been carried out in a diamond anvil cell up to pressures of 180 kbar. The emphasis here is with respect to (a) the effect of particle size on the pressure dependence of the band gap as well as (b) indirect examination of the structural impact of the erbium dopant on the pressure-induced phase transition(s). It is found that in terms of electronic structure these Er-doped Si nanocrystals act very much like indirect gap silicon, with an observed band gap pressure dependence of −1.4 × 10-6 eV/bar. Measurements of the optical spectra in terms of integrated area as a function of pressure of these doped nanoparticles reveal that the first-order phase transition must lie above 180 kbar, substantially elevated from the bulk value of 120 kbar. Thus, doped nanocrystals of this dimension maintain a significant elevation in the phase transition pressure (known in homogeneous Si nanocrystals relative to bulk crystalline Si), but the Er dopant does not introduce the type of structural defects that would lower the energy barrier to such a transformation.

Observation of pressure-induced direct-to-indirect band gap transition in InP nanocrystals

We investigate the quantum size effects in the pressure-induced direct-to-indirect band gap transition in InP nanocrystals. Hydrostatic pressures of up to 13 GPa are applied to two different sizes of InP nanocrystal samples in a diamond anvil cell. The band gap pressure dependence and the nature of the emitting states are studied by photoluminescence (PL) and fluorescence line narrowing (FLN) techniques at 10 K. Pressure-dependent FLN spectra show that the nature of the emitting states at pressures up to 9 GPa is similar to that at ambient pressure, suggesting that no direct-to-indirect transition happens below 9 GPa. For both sizes, the PL peak energy exhibits a strong blueshift with rising pressure until approximately 9 to 10 GPa. Above this pressure, the PL peak position slightly shifts red. Beyond 12 GPa, the band gap emission intensity becomes extremely weak and trap emission dominates the PL spectra. As the pressure is released, both the luminescence intensity and the peak position recover in a fully reversible manner. The change in the sign of the band gap energy pressure dependence and the disappearance of the band edge luminescence indicate the pressure-induced direct-to-indirect band gap transition. Contrary to theoretical calculations, no substantial reduction of the transition pressure is observed in the nanocrystal cases compared to the bulk transition pressure.

Pressure Dependence of Band Gaps in the Quaternary Semiconductors Cu(In, Ga)Se2

Pressure Dependence of Band Gaps in the Quaternary Semiconductors Cu(In, Ga)Se2

Pressure Dependence of Band Gaps in the Quaternary Semiconductors Cu(In, Ga)Se2

We report the photoluminescence and absorption spectra of a series of quaternary chalcopyrite alloys with the formula: CuIn1—xGaxSe2 where x varies between 0 and 1 in steps of 0.25. Using a diamond anvil cell we have studied their band gaps and impurity emission peak energies as a function of pressure. We found that while the band gap of CuIn1—xGaxSe2 varies nonlinearly with x the pressure coefficient (α) varies linearly with x at a rather large rate of dα/dx = 18.6 meV/GPa. We interpret our results in terms of recent theoretical calculations which have been proposed to explain the large difference in α between CuGaSe2 and CuInSe2.

Pressure Dependence of Band Gaps and Deep Centers in Chalcopyrite Semiconductors

We present a review of the effect of high pressure on the electronic, optical and defect properties in chalcopyrite semiconductors with the formula I–III–VI2. We show that the linear pressure coefficients of the band gap in these materials are not constant. While the bulk moduli of this family of semiconductors are rather constant, the dependence of the band gap on volume exhibits systematic trends when the group III cations are varied. We also found that there are deep center emissions whose pressure coefficients are larger than those of the band gap. We propose that the origin of these deep emissions are deep acceptors and their pressure coefficients can be understood in terms of p–d hybridization in the valence bands.