Zinc-blende Semiconductors Research Articles

The manipulation of the physical properties of some typical zinc-blende semiconductors by the electric field

In this research, we regulate the band gaps of some typical zinc-blende semiconductors by applying an external electric field. The variation of the geometric structures and the band gaps of AlP, AlAs, AlSb, GaP, GaAs, ZnO, ZnSe and ZnTe have been studied. We also calculated the stability, density of states, band structures and the charge distribution by the first-principles method based on density functional theory. Moreover, the giant Stark effect coefficients have also been analyzed in detail. From our results, we find that the magnitude and the direction of the electric field has a significant regulation effect on the band gaps and the electronic structures of AlP, AlAs, AlSb, GaP, GaAs, ZnO, ZnSe and ZnTe, which induces a phase transition from semiconductor to metal beyond a certain electric field. Therefore, we can regulate the physical properties of this type of semiconductors by tuning the magnitude and the direction of the electric field. This is very important for practical applications in nanoelectronic devices.

First principle study of the structural, electronic, vibrational, thermodynamic, linear and nonlinear optical properties of zinc-blende ZnSe and ZnTe semiconductors

The first principle investigations of the structural, electronic, linear and nonlinear response properties of the zinc-blende ZnSe and ZnTe are performed based on the density functional theory using a plane-wave pseudopotential approach. The Born effective charges, piezoelectric tensor, phonon frequencies, LO–TO splitting and thermal properties of these compounds are calculated using a linear response method within the density functional theory framework. The macroscopic dielectric function is calculated in the response of the many body effects within the Bethe-Salpeter approach using the Tam-Dancoff approximation. The nonlinear response properties to atomic displacements and electric fields are investigated within the density functional perturbation theory framework based on the 2n+1 theorem as implemented by the ABINIT software. After the calculation of the Kohn–Sham electronic band structures, the correction of the energy band gap is computed using the GW approximation within the many-body perturbation theory framework (MBPT). The results are in excellent agreement with the available experimental and other theoretical results.

Hybrid functional study of nonlinear elasticity and internal strain in zinc-blende III-V materials

We investigate the elastic properties of selected zinc-blende III-V semiconductors. Using hybrid functional density functional theory, we calculate the second- and third-order elastic constants and first- and second-order internal strain tensor components for Ga, In, and Al containing III-V compounds. For many of these parameters, there are no available experimental measurements, and this work is the first to predict their values. The stricter convergence criteria for the calculation of higher-order elastic constants are demonstrated, and arguments are made based on this for extracting these constants via the calculated stresses, rather than the energies, in the context of plane-wave-based calculations. The calculated elastic properties are used to determine the strain regime at which higher-order elasticity becomes important by comparing the stresses predicted by a lower- and a higher-order elasticity theory. Finally, the results are compared with available experimental literature data and previous theory.

First-principles calculations of magnetic and optical properties of Ga<sub>1–x</sub>Cr<sub>x</sub>Sb (x = 0.25, 0.50, 0.75)

As the demand for electronic devices increases continually, the spintronic materials have played an important role in materials science and electronics. Spintronic devices have excellent properties such as non-volatility, low power consumption, and high integration compared with conventional semiconductor devices. In this paper, we investigate the electronic structure, magnetic and optical properties of the semiconductor GaSb doped with 3d transition metal Cr, based on first-principles calculations. The compounds are constructed by replacing some Ga atoms with Cr in zinc-blende GaSb semiconductor, where the concentrations of the Ga atoms replaced are 0, 0.25, 0.50, and 0.75. We adopt the projected plane wave method and the electronic exchange correlation functional PBE in the generalized gradient approximation. Band gap is modified by Heyd-Scuseria-Ernzerhof (HSE06) functional. We study the equilibrium lattice constants of Cr-doped GaSb in zinc-blende structure at different concentrations. The energy of nonmagnetic, ferromagnetic and antiferromagnetic states at the equilibrium lattice constants are compared to identify the ground state. For Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb (<i>x</i> = 0.25, 0.50, 0.75), we find that the most stable state is ferromagnetic state. In the electronic structure of the ground state, the spin-up bands pass through the Fermi level while the spin-down bands each have a direct band gap. The Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb exhibit ferromagnetic half-metallic properties. The magnetic properties at different lattice constants under different concentrations are studied. Our analysis indicates that the Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb have integer Bohr magnetic moments of 3.0, 6.0, 9.0 <i>μ</i><sub>B</sub> for <i>x</i> = 0.25, 0.50 and 0.75, respectively. We find that when the lattice changes fom –5% to 20%, the total magnetic moment for each of Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb still remains the integer Bohr magnetic moment, and the magnetic moment of the Cr increases with the lattice constant increasing. We also find that the ferromagnetisms of Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb have Curie temperatures above room temperature, estimated by mean-field method. The p-d electron hybridization occurs in Cr-3d orbital and Sb-5p orbital, and the electron state density distribution of Cr-3d is transferred, that is, the electron orbital hybridization makes the total electron state density of crystal material redistributed, which is the main reason why Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb (<i>x</i> = 0.25, 0.50, 0.75) present ferromagnetic half-metallic properties. Additionally, the Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb have good absorption ability in the infrared region, compatible with zinc-blende semiconductors such as GaSb, which makes Ga<sub>1–<i>x</i></sub>Cr<sub><i>x</i></sub>Sb have promising potential applications in both spintronic devices and infrared optoelectronic devices.

Even and odd harmonics-enhanced supercontinuum generation in zinc-blende semiconductors

We report on even and odd harmonics-enhanced supercontinuum generation in polycrystalline ZnS and ZnSe samples, as pumped by femtosecond mid-infrared pulses. We demonstrate that efficient generation of multiple harmonics takes place due to random quasi-phase matching, which is an intrinsic property of polycrystalline structure that supports multiple simultaneous three-wave mixing processes over a broad wavelength range. More specifically, using sub-μJ, 60 fs, 3.6 μm input pulses, we measured multi-octave supercontinuum spectra spanning the 0.4–5 μm and 0.5–5 μm wavelength ranges in ZnS and ZnSe samples of few mm thickness, respectively. Even and odd harmonics up to the 10th order in ZnS and up to the 8th order in ZnSe were recorded with the input pulses at 4.6 μm. In contrast, filamentation in ZnTe single crystal is shown to produce only a moderate spectral broadening, which is accompanied by the generation of just second and third harmonics, highlighting the advantages of the polycrystalline structure of zinc-blende semiconductors to generate ultrabroadband radiation.

Third harmonic generation on exciton-polaritons in bulk semiconductors subject to a magnetic field

We report on a comprehensive experimental and theoretical study of optical third harmonic generation (THG) on the exciton-polariton resonances in the zinc-blende semiconductors GaAs, CdTe, and ZnSe subject to an external magnetic field, representing a topic that had remained unexplored so far. In these crystals, crystallographic THG is allowed in the electric-dipole approximation, so that no strong magnetic-field-induced changes of the THG are expected. Therefore, it comes as a total surprise that we observe a drastic enhancement of the THG intensity by a factor of fifty for the $1s$-exciton-polariton in GaAs in magnetic fields up to 10 T. In contrast, the corresponding enhancement is moderate for CdTe and almost neglectful for ZnSe. In order to explain this strong variation, we develop a microscopic theory accounting for the optical harmonics generation on exciton-polaritons and analyze the THG mechanisms induced by the magnetic field. The calculations show that the increase of THG intensity is dominated by the magnetic field enhancement of the exciton oscillator strength which is particularly strong for GaAs in the studied range of field strengths. The much weaker increase of THG intensity in CdTe and ZnSe is explained by the considerably larger exciton binding energies, leading to a weaker modification of their oscillator strengths by the magnetic field.

Recent Progress in High-Mobility Organic Transistors: A Reality Check.

Over the past three decades, significant research efforts have focused on improving the charge carrier mobility of organic thin-film transistors (OTFTs). In recent years, a commonly observed nonlinearity in OTFT current-voltage characteristics, known as the "kink" or "double slope," has led to widespread mobility overestimations, contaminating the relevant literature. Here, published data from the past 30 years is reviewed to uncover the extent of the field-effect mobility hype and identify the progress that has actually been achieved in the field of OTFTs. Present carrier-mobility-related challenges are identified, finding that reliable hole and electron mobility values of 20 and 10 cm2 V-1 s-1 , respectively, have yet to be achieved. Based on the analysis, the literature is then reviewed to summarize the concepts behind the success of high-performance p-type polymers, along with the latest understanding of the design criteria that will enable further mobility enhancement in n-type polymers and small molecules, and the reasons why high carrier mobility values have been consistently produced from small molecule/polymer blend semiconductors. Overall, this review brings together important information that aids reliable OTFT data analysis, while providing guidelines for the development of next-generation organic semiconductors.

Irradiated three-dimensional Luttinger semimetal: A factory for engineering Weyl semimetals

We study the interaction between elliptically polarized light and a three-dimensional Luttinger semimetal with quadratic band touching using Floquet theory. In the absence of light, the touching bands can have the same or the opposite signs of the curvature; in each case, we show that simply tuning the light parameters allows us to create a zoo of Weyl semimetallic phases. In particular, we find that double and single Weyl points can coexist at different energies, and they can be tuned to be type I or type II. We also find an unusual phase transition, in which a pair of Weyl nodes form at finite momentum and disappear off to infinity. Considering the broad tunability of light and abundance of materials described by the Luttinger Hamiltonian, such as certain pyrochlore iridates, half-Heuslers and zinc-blende semiconductors, we believe this work can lay the foundation for creating Weyl semimetals in the lab and dynamically tuning between them.

Reduction of Charge Traps and Stability Enhancement in Solution-Processed Organic Field-Effect Transistors Based on a Blended n-Type Semiconductor.

Solution-processed n-type organic field-effect transistors (OFETs) are essential elements for developing large-area, low-cost, and all organic logic/complementary circuits. Nonetheless, the development of air-stable n-type organic semiconductors (OSCs) lags behind their p-type counterparts. The trapping of electrons at the semiconductor-dielectric interface leads to a lower performance and operational stability. Herein, we report printed small-molecule n-type OFETs based on a blend with a binder polymer, which enhances the device stability due to the improvement of the semiconductor-dielectric interface quality and a self-encapsulation. Both combined effects prevent the fast deterioration of the OSC. Additionally, a complementary metal-oxide semiconductor-like inverter is fabricated depositing p-type and n-type OSCs simultaneously.

Kane Fermion in a Two-Dimensional π-Conjugated Bis(iminothiolato)nickel Monolayer.

Massless Kane fermions revealed in zinc-blende semiconductors have recently gained interest in the broad study of relativistic materials. In particular, two-dimensional (2D) Kane fermions were expected to be hybrids of pseudospin-1 and -1/2 Dirac fermions. Based on first-principles calculations, we demonstrated that 2D Kane fermions can be realized in a recently synthesized metal-organic framework, namely, bis(iminothiolato)nickel monolayer. A slight compression takes the system from a semimetal to a semiconductor. At the critical strain of ∼1%, the upper and lower conical bands linearize and touch at a single point intersecting a flat band, showing the same dispersion as the pseudospin-1 Dirac-Weyl systems. We adopted a tight-binding Hamiltonian of a line-centered honeycomb lattice to reveal the origins and topology of the electronic band structure. The coexistence of Kane-type and Dirac-type spectra in the bis(iminothiolato)nickel monolayer is expected to benefit the study of multi quasiparticle effects.

Investigating coating method induced vertical phase distribution in polymer-fullerene organic solar cells

The morphologies of bulk heterojunction (BHJ) films of blended semiconductor of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) deposited by doctor blading and spin coating were investigated. Controlled phase separation in BHJ organic/polymer solar cells (OSCs) were achieved using doctor blading. The results revealed that the coating method induced a significant difference in the film morphology. The vertical phase distribution of the BHJ layer fabricated by doctor blading was uniform, while uneven phase distribution was observed in spin coated BHJ layer. The uniform phase distribution in the doctor blading coated film resulted in higher charge carrier mobility and power conversion efficiency in solar cell than those in films fabricated from spin coating. The results demonstrated that doctor blading has advantages not only in large area high throughput and roll-to-roll compatibility, but also in better control of film morphology to achieve high efficiency consistently in OSC devices.

Charge Density and Band Offsets at Heterovalent Semiconductor Interfaces

The well‐known insensitivity of the band offset (BO) of isovalent heterojunctions with the zincblende structure to the orientation, abruptness, and atomic structure of the interface was recently shown to be attributable to a localness in the dependence of charge density on the atomic structure. In contrast, a sharp dependence of the BO on interface specifics has been observed at heterovalent heterojunctions. Here, detailed analyses of the relationship between the BO, interface structure, and charge distribution have been carried out for many lattice‐matched heterovalent interfaces between zincblende and diamond structure semiconductors. From thermodynamic considerations, three types of neutral interfaces were investigated, each with equal densities of donor‐ and acceptor‐like heterovalent bonds, constructible in all orientations. Distinctively different, yet approximately orientation‐independent, valence BOs were found. The equilibrium charge density of the heterovalent interface could be recreated with the charge densities of bulk semiconductors and oligo‐cells. Because charge transfer between heterovalent bonds is identifiable with that for dopants in semiconductor and its effect accountable by linear response, a combination of neutral polyhedra theory, previously developed for isovalent heterojunctions, and dielectric screening theory was found to explain BO trends throughout, allowing a strategy that facilitates adjustment in the BO of all isovalent heterojunctions.

Graphitic nanofilms of zinc-blende materials: ab initio calculations

Ab initio calculations on ultra-thin nanofilms of 25 kinds of zinc-blende semiconductors demonstrate their stable geometry structures growth along (1 1 1) surface. Our results show that the (1 1 1) surfaces of 9 kinds of zinc-blende semiconductors can transform into a stable graphitelike structure within a certain thickness. The tensile strain effect on the thickness of graphitic films is not obvious. The band gaps of stable graphitic films can be tuned over a wide range by epitaxial tensile strain, which is important for applications in microelectronic devices, solar cells and light-emitting diodes.

Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction**Project supported by the Research Plan in Shaanxi Province, China (Grant No. 2016GY-085), the Opening Project of Key Laboratory of Microelectronic Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences (Grant No. 90109162905), the Fundamental Research Funds for the Central Universities (Grant No. 17-H863-04-ZT-001-019-01),

The analysis of threading dislocation density (TDD) in Ge-on-Si layer is critical for developing lasers, light emitting diodes (LEDs), photodetectors (PDs), modulators, waveguides, metal oxide semiconductor field effect transistors (MOSFETs), and also the integration of Si-based monolithic photonics. The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope (TEM). However, high-resolution x-ray diffraction (HR-XRD) rocking curve provides an optional method to analyze the TDD in Ge layer. The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors. In this paper, this method is extended to the case of strained Ge-on-Si layers. The HR-XRD scan is measured and Ge (004) single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer. The rocking curve full width at half maximum (FWHM) broadening by incident beam divergence of the instrument, crystal size, and curvature of the crystal specimen is subtracted. The TDDs of samples A and B are calculated to be 1.41 × 108 cm−2 and 6.47 × 108 cm−2, respectively. In addition, we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.

On the pressure-dependent phonon characteristics and anomalous thermal expansion coefficient of 3C-SiC

By exploiting a realistic rigid-ion model (RIM) in the quasi-harmonic approximation, we have calculated the pressure- and temperature-dependent phonon characteristics of cubic silicon carbide (3C-SiC). All the RIM parameters at ambient (1atm or P=0) and high pressure (P=22.5GPa) are carefully optimized by using successive least-square fitting procedures – incorporating critical-point phonon energies as input while the lattice, elastic constants and their pressure derivatives are employed as constraints. For P>0, we strongly recommend the need of high resolution temperature-dependent second-order Raman scattering measurements to help identify the shifts of optical and acoustical phonons perceived in the two-phonon density of states. Unlike many zinc-blende semiconductors, the present lattice dynamical study of 3C-SiC exhibited no negative thermal expansion (NTE) coefficient α(T) at low temperatures T<100K. The mechanism responsible for the absence of NTE behavior is identified and discussed in terms of the bonding and elastic properties of 3C-SiC with comparison to those of diamond (C) and silicon (Si) materials.

On understanding the chemical origin of band gaps.

Conceptual DFT and quantum chemical topology provide two different approaches based on the electron density to grasp chemical concepts. We present a model merging both approaches, in order to obtain physical properties from chemically meaningful fragments (bonds, lone pairs) in the solid. One way to do so is to use an energetic model that includes chemical quantities explicitly, so that the properties provided by conceptual DFT are directly related to the inherent organization of electrons within the regions provided by topological analysis. An example of such energy model is the bond charge model (BCM) by Parr and collaborators. Bonds within an ELF-BCM coupled approach present very stable chemical features, with a bond length of ca. 1 Å and 2[Formula: see text]. Whereas the 2[Formula: see text] corroborate classical views of chemical bonding, the fact that bonds always expand along 1 Å introduces the concept of geometrical transferability and enables estimating crystalline cell parameters. Moreover, combining these results with conceptual DFT enables deriving a model for the band gap where the chemical hardness of a solid is given by the bond properties, charge, length, and a Madelung factor, where the latter plays the major role. In short, the fundamental gap of zinc-blende solids can be understood as given by a 2[Formula: see text] bond particle asymmetrically located on a 1 Å length box and electrostatically interacting with other bonds and with a core matrix. This description is able to provide semi-quantitative insight into the band gap of zinc-blende semiconductors and insulators on equal footing, as well as a relationship between band gap and compressibility. In other words, merging these different approaches to bonding enables to connect measurable macroscopic behavior with microscopic electronic structure properties and to obtain microscopic insight into the chemical origin of band gaps, whose prediction is still nowadays a difficult task. Graphical Abstract Conceptual DFT couples to quatum chemcial topology to explain the band gap of zinc-blende solids.

Modal phase matching in nanostructured zinc-blende semiconductors for second-order nonlinear optical interactions

We demonstrate enhanced second-harmonic generation in arrays of nanowaveguides satisfying modal-phase-matching condition, both theoretically and experimentally. The overlap of interacting fields de ...

Nonradiative Step Facets in Semiconductor Nanowires.

One of the main advantages of nanowires for functional applications is their high perfection, which results from surface image forces that act on line defects such as dislocations, rendering them unstable and driving them out of the crystal. Here we show that there is a class of step facets that are stable in nanowires, with no long-range strain field or dislocation character. In zinc-blende semiconductors, they take the form of Σ3 (112) facets with heights constrained to be a multiple of three {111} monolayers. Density functional theory calculations show that they act as nonradiative recombination centers and have deleterious effects on nanowire properties. We present experimental observations of these defects on twin boundaries and twins that terminate inside GaAsP nanowires and find that they are indeed always multiples of three monolayers in height. Strategies to use the three-monolayer rule during growth to prevent their formation are discussed.

Flexible-Blade Coating of Small Molecule Organic Semiconductor for Low Voltage Organic Field Effect Transistor

A flexible-blade coating (FBC) approach, using a simple thin and flexible steel sheet as the meniscus guide, is developed to deposit the blended small molecule organic semiconductor (OSC) solution on substrate surface with pre-fabricated electrode patterns. During coating, the bottom edge of the used flexible steel film touches the substrate surface, but can bend up adapting to the surface morphology variation without causing any damages to the bottom electrodes. With this approach, little amount of very dilute ink solution can be used to coat the channel film, resulting in the greatest material saving among all reported methods. It is shown that, by using the FBC at a moving speed of 12 mm/s to deposit the OSC layer, all solution processed low-voltage organic field effect transistor composed of another polymer gate dielectric layer and inkjet printed metal electrodes were achieved over relatively large area with high performance and good uniformity.

Wurtzite spin lasers

Semiconductor lasers are strongly altered by adding spin-polarized carriers. Such spin lasers could overcome many limitations of their conventional (spin-unpolarized) counterparts. While the vast majority of experiments in spin lasers employed zinc-blende semiconductors, the room temperature electrical manipulation was first demonstrated in wurtzite GaN-based lasers. However, the underlying theoretical description of wurtzite spin lasers is still missing. To address this situation, focusing on (In,Ga)N-based wurtzite quantum wells, we develop a theoretical framework in which the calculated microscopic spin-dependent gain is combined with a simple rate equation model. A small spin-orbit coupling in these wurtzites supports simultaneous spin polarizations of electrons and holes, providing unexplored opportunities to control spin lasers. For example, the gain asymmetry, as one of the key figures of merit related to spin amplification, can change the sign by simply increasing the carrier density. The lasing threshold reduction has a nonmonotonic depenedence on electron spin polarization, even for a nonvanishing hole spin polarization.