Interband Optical Absorption Research Articles

Interband optical absorption coefficient of the diluted magnetic semiconductor ellipsoid quantum dot with Rashba spin orbit interaction

Interband optical absorption coefficient of the diluted magnetic semiconductor ellipsoid quantum dot with Rashba spin orbit interaction

Photocarrier generation mechanism of graphene-based field effect device

The carrier generation in a photodetecting device plays a critical role in the enhancement of photocurrent. Here we perform photocurrent measurements on graphene-based photodetecting device and unveil three carrier generation mechanisms, namely, (I) thermally assisted- and (II) optically induced- excitation of in-gap defect state electron, and (III) inter-band optical absorption of bulk Si. We further determine their carrier supply strength defined as P = dn/dt, which are P(I) = 2.09×1010 /cm⋅2 s, P(II) = 2.15×1010 /cm⋅2s, and P(III) = 3.55×1011 /cm⋅2s, respectively. In addition, we show that the characteristic IV behavior induced by the gate voltage cycling can be interpreted in terms of the three carrier generation mechanisms. This study provides a useful guide to designing practical graphene-based photodetecting devices.

Theoretical Insights into Photovoltaic Application of a Novel Family of Perovskite‐Inspired Pb‐Free Metal Halide Materials

Organic–inorganic halide perovskite have shown great promise for photovoltaic applications due to their unprecedented optoelectronic properties and low manufacturing cost. However, the commercialization of this emerging technology is hampered by its thermal instability and intrinsic Pb‐toxicity. Here, we report first‐principles investigations on stability and optoelectronic properties of a series of all‐inorganic lead‐free metal halide perovskite‐like materials AMX4 (A = Cs, Ag, and Rb; M = In, Sb, and Bi; X = Cl, Br, and I). Our calculations show that AgSbI4 and AgBiI4 have direct bandgaps of 1.63 and 1.44 eV, which possess strong interband optical absorption (≈105 cm−1). Based on these favorable properties, we also simulated the AgSbI4‐ and AgBiI4‐based thin film solar cells with the SCAPS‐1D code and achieve high PCE of 24.19% and 26.70%, respectively. These results reveal that the AMX4 perovskite‐like materials could serve as potential alternatives to Pb‐based halide perovskites in photovoltaic devices.

Optical Properties of Conical Quantum Dot: Exciton-Related Raman Scattering, Interband Absorption and Photoluminescence.

The current work used the effective mass approximation conjoined with the finite element method to study the exciton states in a conical GaAs quantum dot. In particular, the dependence of the exciton energy on the geometrical parameters of a conical quantum dot has been studied. Once the one-particle eigenvalue equations have been solved, both for electrons and holes, the available information on energies and wave functions is used as input to calculate exciton energy and the effective band gap of the system. The lifetime of an exciton in a conical quantum dot has been estimated and shown to be in the range of nanoseconds. In addition, exciton-related Raman scattering, interband light absorption and photoluminescence in conical GaAs quantum dots have been calculated. It has been shown that with a decrease in the size of the quantum dot, the absorption peak has a blue shift, which is more pronounced for quantum dots of smaller sizes. Furthermore, the interband optical absorption and photoluminescence spectra have been revealed for different sizes of GaAs quantum dot.

Influence of external fields on the exciton binding energy and interband absorption in a double inverse parabolic quantum well

Ground-state binding energy and optical absorption coefficient of exciton in a symmetric double inverse parabolic quantum well system in the presence of external electric and magnetic fields are investigated theoretically. Numerical calculations have been carried out with the variational technique considering the single-band effective mass approximations. Results reveal that the excitonic binding energy and interband optical absorption depend on significantly on the geometrical and structural parameters defining carriers’ double inverse parabolic confinement potential, the aluminum concentration at the well center, the electric field, and the magnetic field. The exciton binding energy is a decreasing (increasing) function of the electric field (magnetic field). The increase in aluminum concentration creates a blueshift at the resonance peak positions. As a result, the tunability of the excitonic effects is expected to be of importance in developing stable and high-efficiency nanoscale excitonic optoelectronic devices . • Analyses of double inverse parabolic quantum well. • Exciton binding energy. • Interband transitions. • Electric and magnetic field effects.

An image interaction approach to quantum-phase engineering of two-dimensional materials

Tuning electrical, optical, and thermal material properties is central for engineering and understanding solid-state systems. In this scenario, atomically thin materials are appealing because of their sensitivity to electric and magnetic gating, as well as to interlayer hybridization. Here, we introduce a radically different approach to material engineering relying on the image interaction experienced by electrons in a two-dimensional material when placed in proximity of an electrically neutral structure. We theoretically show that electrons in a semiconductor atomic layer acquire a quantum phase resulting from the image potential induced by the presence of a neighboring periodic array of conducting ribbons, which in turn modifies the optical, electrical, and thermal properties of the monolayer, giving rise to additional interband optical absorption, plasmon hybridization, and metal-insulator transitions. Beyond its fundamental interest, material engineering based on the image interaction represents a disruptive approach to tailor the properties of atomic layers for application in nanodevices.

Discovery of New Plasmonic Metals via High‐Throughput Machine Learning (Advanced Optical Materials 18/2022)

Ethan P. Shapera and André Schleife have constructed, validated, and applied machine learning models to search an online database for potential new plasmonic materials (see article number 2200158). The authors predict three high-quality-factor metals: AlCu3 (bottom on the cover, plasma frequency = 9.0 eV), ZnCu (middle, plasma frequency = 9.59 eV), and ZnGa3 (top, plasma frequency = 10.64 eV). Furthermore, ZnCu is found to have no interband optical absorption up to 1.9 eV. [Cover image generated by Xinzhi Hu and Ye Lin.]

Optical absorption in two-dimensional materials with tilted Dirac cones

The interband optical absorption of linearly polarized light by two-dimensional (2D) semimetals hosting tilted and anisotropic Dirac cones in the band structure is analysed theoretically. Supercritically tilted (type-II) Dirac cones are characterized by an absorption that is highly dependent on the incident photon polarization and frequency and is tunable by changing the Fermi level with a back-gate voltage. Type-II Dirac cones exhibit open Fermi surfaces and large regions of the Brillouin zone where the valence and conduction bands sit either above or below the Fermi level. As a consequence, unlike their subcritically tilted (type-I) counterparts, type-II Dirac cones have many states that are Pauli blocked even when the Fermi level is tuned to the level crossing point. We analyze the interplay of the tilt parameter with the Fermi velocity anisotropy, demonstrating that the optical response of a Dirac cone cannot be described by its tilt alone. As a special case of our general theory, we discuss the proposed 2D type-I semimetal 8-$Pmmn$ borophene. Guided by our in-depth analytics, we develop an optical recipe to fully characterize the tilt and Fermi velocity anisotropy of any 2D tilted Dirac cone solely from its absorption spectrum. We expect our paper to encourage Dirac cone engineering as a major route to create gate-tunable thin-film polarizers.

Electrically Tunable Nonequilibrium Optical Response of Graphene.

The ability to tune the optical response of a material via electrostatic gating is crucial for optoelectronic applications, such as electro-optic modulators, saturable absorbers, optical limiters, photodetectors, and transparent electrodes. The band structure of single layer graphene (SLG), with zero-gap, linearly dispersive conduction and valence bands, enables an easy control of the Fermi energy, EF, and of the threshold for interband optical absorption. Here, we report the tunability of the SLG nonequilibrium optical response in the near-infrared (1000–1700 nm/0.729–1.240 eV), exploring a range of EF from −650 to 250 meV by ionic liquid gating. As EF increases from the Dirac point to the threshold for Pauli blocking of interband absorption, we observe a slow-down of the photobleaching relaxation dynamics, which we attribute to the quenching of optical phonon emission from photoexcited charge carriers. For EF exceeding the Pauli blocking threshold, photobleaching eventually turns into photoinduced absorption, because the hot electrons’ excitation increases the SLG absorption. The ability to control both recovery time and sign of the nonequilibrium optical response by electrostatic gating makes SLG ideal for tunable saturable absorbers with controlled dynamics.

Exciton-Related Raman Scattering, Interband Absorption and Photoluminescence in Colloidal CdSe/CdS Core/Shell Quantum Dots Ensemble.

By using the numerical discretization method within the effective-mass approximation, we have theoretically investigated the exciton-related Raman scattering, interband absorption and photoluminescence in colloidal CdSe/CdS core/shell quantum dots ensemble. The interband optical absorption and photoluminescence spectra have been revealed for CdSe/CdS quantum dots, taking into account the size dispersion of the ensemble. Numerical calculation of the differential cross section has been presented for the exciton-related Stokes–Raman scattering in CdSe/CdS quantum dots ensemble with different mean sizes.

Interband optical absorption obtained by pseudopotential method for type-II InAs/GaSb SL photodetectors

We have calculated interband optical absorption for InAs/GaSb based type-II superlattice (SL) structures. The empirical pseudopotential method (EPM) has been used as an alternative to the k.p method since it is less sophisticated while providing similar results in the mid wavelength infrared range and long wavelength infrared range atmospherics bands for comparison. EPM results show that the bandgap wavelengths of SLs have been predicted with the underestimating of 0.4 µm. This corresponds to an uncertainty of less than 0.3 monolayer in the layer width. The theoretical estimation is comparable with the uncertainty of the layer width during the growth process. Heterostructures or SLs with their ternary and quaternary alloys can be calculated by this method to identify electronic and optical parameters for both intersubband and interband applications.

Plasmon extinguishment by bandedge shift identified as a second-order spectroscopic differentiation

Abstract Optical excitation of metallic nanostructures induces strong intraband transitions, leaving transient depletion below the Fermi level, which allows transient interband transition to this depletion band. This is equivalent to the lowering of the threshold for interband transitions and pushes the plasmonic band to the red. As a result, localized surface plasmon resonance (LSPR) is “extinguished” or “quenched” around the bandedge, in contrast, the interband optical absorption becomes enhanced and redshifted. The corresponding transient absorption (TA) signals have equal lifetimes and opposite signs. Moreover, the TA spectrum is found to be a second-order differential of the steady-state optical extinction spectrum over the studied band. This is a commonly existing mechanism for metallic nanostructures and verified with gold in this work. Such a discovery is completely different from the optical-excitation-induced redshift of LSPR through enhanced electronic scattering and is important for understanding the ultrafast spectroscopic response of plasmonic nanostructures with clear photophysical insights, supplying solid basis for exploring optical logic device and optical data processing techniques.

Optical conductivity of triple point fermions

As a low-energy effective theory on non-symmorphic lattices, we consider a generic triple point fermion Hamiltonian, which is parameterized by an angular parameter λ. We find strong λ dependence in both Drude and interband optical absorption of these systems. The deviation of the T 2 coefficient of the Drude weight from Dirac/Weyl fermions can be used as a quick way to optically distinguish the triple point degeneracies from the Dirac/Weyl degeneracies. At the particular λ = π/6 point, we find that the ‘helicity’ reversal optical transition matrix element is identically zero. Nevertheless, deviating from this point, the helicity reversal emerges as an absorption channel.

Estudo das propriedades ópticas em pontos quânticos de CdTe carregados

In this article we theoretically study how the presence of charge carriers added to the conduction and valence band of a spherical CdTe quantum dot affects the optical properties, especially the absorption coefficient. For this study, we simulated the interband optical absorption spectrum for incident light with circular polarizations on the left (ê-), on the right (ê+) and linear (êz). We also consider Coulomb's interaction between optically excited and added carriers.

Exciton Fine Structure in Lead Chalcogenide Quantum Dots: Valley Mixing and Crucial Role of Intervalley Electron-Hole Exchange.

We study the exciton fine structure in quantum dots of multivalley lead chalcogenides. We demonstrate that intervalley electron-hole exchange interaction, ignored in previous studies, dramatically modifies the exciton fine structure and leads to appearance of the ultrabright valley-symmetric spin-triplet exciton state dominating interband optical absorption. Valley mixing leads to brightening of other symmetry-allowed spin-triplet states which dominate low-temperature photoluminescence.

Optical absorption window in Na3Bi based three-dimensional Dirac electronic system

We present a detailed theoretical study of the optoelectronic properties of a Na3Bi based three-dimensional Dirac electronic system (3DDES). The optical conductivity is evaluated using the energy-balance equation derived from a Boltzmann equation, where the electron Hamiltonian is taken from a simplified k⋅p approach. We find that for short-wavelength irradiation, the optical absorption in Na3Bi is mainly due to inter-band electronic transitions. In contrast to the universal optical conductance observed for graphene, the optical conductivity for Na3Bi based 3DDES depends on the radiation frequency but not on temperature, carrier density, and electronic relaxation time. In the radiation wavelength regime of about 5μm<λ<200 μm, an optical absorption window is found. This is similar to what is observed in graphene. The position and width of the absorption window depend on the direction of the light polarization and sensitively on temperature, carrier density, and electronic relaxation time. Particularly, we demonstrate that the inter-band optical absorption channel can be switched on and off by applying the gate voltage. This implies that similar to graphene, Na3Bi based 3DDES can also be applied in infrared electro-optical modulators. Our theoretical findings are helpful in gaining an in-depth understanding of the basic optoelectronic properties of recently discovered 3DDESs.

Resistive Switching in Metal–Oxide–Semiconductor Structures with GeSi Nanoislands on a Silicon Substrate

It is shown that self-forming GeSi nanoislands built into the dielectric–semiconductor interface in the Si(001)-based metal–oxide–semiconductor (MOS) structures with the SiOx and ZrO2(Y) dielectric layers obtained by magnetron sputtering initiate bipolar resistive switching without preliminary electroforming. The I–V characteristics and electrical parameters of the MOS structures in the high- and low-resistance states have been investigated. The change in the charge incorporated in the dielectric at the dielectric–semiconductor interface during resistive switching has been established, which is related to the formation and destruction of conducting filaments. The optically stimulated switching of the MOS structures with the ZrO2(Y) dielectric layer from the high- to low-resistance state has been observed, which is caused by an increase in the conductivity of the space charge region in the Si substrate due to the interband optical absorption in Si leading to the voltage redistribution between Si and ZrO2(Y). A difference between the shapes of the low-signal photovoltage spectra of the MOS structures in the spectral region of the Si intrinsic photosensitivity in the high- and low-resistance states related to the leakage of photoexcited carriers from Si into a metal electrode through filaments has been found.

Linear interband optical refraction and absorption in strained black phosphorene

Strain effects have been widely addressed in monolayer black phosphorus (MBP) due to its significant influence on the orbital hybridization of atoms. In this theoretical contribution, we use the tight-binding model, the Harrison rule and the Kubo formula to describe the optical refraction and absorption of MBP in detail. The analytical study of the band gap in strained MBP demonstrates electronic phase transitions from semiconductor-to-semimetal/metal and semiconductor-to-insulator, in which both the compressive and tensile strains act linearly on the band gap alterations. The critical strains corresponding to these phase transitions are fully characterized as well. Our calculations show that the variation of the refraction inflections and absorption peaks depends on the strained band gap, however; the band gap changes under out-of-plane strains are different than the in-plane ones. The conditions under which this discrepancy is significant and/or negligible are investigated. Moreover, the dedication of minimal/maximal optical refraction and/or absorption in MBP to both in-plane and out-of-plane strains are fully addressed. Our theoretical results clarify the strain-induced interplay between the band gap and optical properties to propose a wide range of applications in nano-optoelectronics.

Optical absorption by a nanosystem with dielectric quantum dots

The mechanisms of formation of the spectra of interband optical absorption in nanosystems containing aluminum oxide quantum dots, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the band of the electron–hole pair states cause absorption in the ultraviolet wavelengths and cause the experimentally observed significant blurring of the absorption band.

Effect of gravity and electromagnetic field on the spectra of cylindrical quantum dots together with AB flux field

In this work, we study the spectral properties of electron quantum dots (QDs) confined in 2D parabolic harmonic oscillator influenced by gravity, external uniform electromagnetic field together with an Aharonov–Bohm (AB) flux field. Our calculations are based on the Nikiforov–Uvarov method and we obtain exact solutions for the energy levels and normalized wave functions. The interband optical absorption QDs of the parabolic spherical shape in GaAs is studied theoretically and the total optical absorption coefficient has been calculated by using the energy eigenvalues spectra and the corresponding wave functions.