Te Semiconductor Research Articles

The electronic structure, optical, and transport properties of novel SrScCu3M4 (M = Se, Te) semiconductors

Abstract The density functional theory is used to investigate the complex relationships between the physical properties of the novel quaternary SrScCu3M4 (M = Se, Te) semiconductors. The computed negative formation energy values of these materials demonstrate their stable nature. The distribution of ELF around chalcogens and Cu atoms shows substantial localization, indicating strong covalent bonding. The phonon dispersion curves show that they possess excellent structure stability with no negative frequencies. The s/p states of Se and s/p/d of Te play minor roles, while Cu-d orbitals possess a considerable influence on the valence band region. The calculated band gaps without SOC for SrScCu3Se4 and SrScCu3Te4 are 1.29, and 0.90, respectively. The predicted energy gap values with SOC for SrScCu3Se4 and SrScCu3Te4 are 1.35, and 0.87, respectively. SrScCu3Se4 is a harder and more compressible material than SrScCu3Te4, as confirmed by its higher bulk modulus. The ε1(ω) values decrease and ultimately become negative, which suggests these materials are reflective. SrScCu3Te4 exhibits plasmon resonance at a high energy domain compared to SrScCu3Se4, resulting in a greater loss function. The current study can establish the potential efficiency of these materials in cutting-edge optoelectronic devices.

Exploring novel Zn2SeX (X=S, Te) ternary chalcogenide: Studying the effect of chalcogen substitution on optoelectronic, and thermoelectric performance

Ternary-type semiconductor chalcogenide materials are distinguished by their outstanding thermal performance and tunable optoelectronic features. The electronic structure, optical, and transport features of novel Zn2SeX ternary (X=S, Te) semiconductors are investigated by employing the widely used density functional theory. Based on the band structure investigation, these materials were anticipated tohave a direct energy gap. The results demonstrated that direct energy losses were caused by the orbitals hybridization of S-p and the Se/Te-d in both materials. Compared to Zn2SeTe, Zn2SeS has a wider band gap at the Γ-point, meaning that electrons will have a lower effective mass and atoms possess a greater effective mass. The elements of the complex dielectric function and the significant optical properties were explored for potential use in optoelectronic applications. The unique peaks in I(ω) confirm extensive absorption in the UV range. They may be employed as very effective ultraviolet-reflecting materials based on the peaks in the reflection spectrum that have been observed. Since both materials positive Seebeck coefficient display p-type conductivity over the whole temperature range.

Spin valve effect in the van der Waals heterojunction of Fe3GeTe2/tellurene/Fe3GeTe2

Spintronic devices are regarded as prime candidates for addressing the demands of emergent applications such as in-memory computing and the Internet of Things, characterized by requirements for high speed, low energy consumption, and elevated storage density. Among these, spin valves, serving as fundamental structures of magnetic random-access memory, have garnered substantial attention in recent years. This study introduces an all van der Waals (vdW) heterostructure composed of Fe3GeTe2 (FGT)/tellurene/FGT, wherein a thin layer of Weyl semiconductor Te is interposed between two ferromagnetic FGT layers. The proposed configuration exhibits a characteristic spin valve effect at temperatures below 160 K. This effect is attributed to spin-dependent transport and spin-dependent scattering phenomena occurring at the interfaces of the constituent materials. Furthermore, as temperature decreases, the magnetoresistance ratio (MR) of the device increases, indicative of the heightened polarization ratio of FGT, with an MR of 0.43% achievable as the temperature approaches 5 K. This investigation elucidates the underlying operational mechanisms of two-dimensional spin valve devices and lays the groundwork for the realization of spin-based integrated circuits.

Insights into the optoelectronic, thermodynamic, and thermoelectric properties of novel BaYCuX3 (X = Se, Te) semiconductors from first-principles investigation

The widely used density functional theory was employed to study an intricate relationship of the optoelectronic, thermodynamic, and transport features of novel quaternary BaYCuX3 (X = Se, Te) semiconductors. The conduction band region is significantly impacted by the Ba-d and Y-d states, with negligible contributions from the S-s/p/d and Te-s/p/d states. The valence and conduction bands peak at the high symmetry Γ and Y sites, revealing an indirect energy band nature. The predicted band gaps for the BaYCuSe3 and BaYCuTe3 using the WC-GGA and TB-mBJ approximations are 0.96, 1.31 eV, and 0.54, 0.89 eV, respectively. The small atomic size of selenium in BaYCuSe3 material contributes to strong bonding, resulting in a larger energy gap as compared to BaYCuTe3. Maximum values of ε1(ω) drop as photon frequency increases, eventually approaching negative in some energy ranges. The absorption coefficient spectra shifted toward lower energy as the anion changed from Se to Te. Furthermore, the BaYCuTe3 has plasmon resonances at higher energies as compared to BaYCuSe3, resulting in increased energy loss. Furthermore, the BaYCuTe3 material exhibits maximum thermal conductivity than BaYCuSe3 across the whole temperature range.

Insights into optoelectronic, thermodynamic, and thermoelectric properties of novel GePtCh (Ch = S, Se, Te) semiconductors: first-principles perspective

Ternary chalcogenides are often studied for their remarkable heat resistance and flexible optical properties. We used density functional theory and examine complicated connections between the various physical features of the exclusive GePtCh (Ch = S, Se, and Te) ternary chalcogenides. The valence band is formed by the hybridization of the Ge-s/p/d, Pt-s/p/d, S-p, Se-p, and Te-p orbitals in the energy range of −6.0 eV to 0 eV. The materials under consideration are confirmed as indirect bandgap materials with estimated energy gaps of 1.29 eV, 0.86 eV, and 0.48 eV, respectively. By substituting Se and Te for S reduced the bandgap in these materials. The complex dielectric function’s components, absorption coefficients, real optical conductivity, energy loss functions, refractive index, reflectivity, and extinction coefficient, are studied and examined to identify their potential use in optoelectronic applications. The thermodynamic parameters of these ternary systems are calculated by employing the quasi-harmonic Debye model. The materials are suitable for thermoelectric devices, as evidenced by their considerable and outstanding thermoelectric features. The GePtTe possessed the highest absorption, indicating that it is a suitable material for the use in optoelectronic applications.

Short-Wave Infrared Colloidal QD Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers.

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, nanosecond-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, record 4ns response time in PbS-based QDPDs that operate at SWIR wavelengths is reported, a result reaching the requirement of SWIR light detection and ranging based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers. Based on these results, it is estimated that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-nanosecond response time.

Optimization of Mechanical and Thermoelectric Properties of SnTe-Based Semiconductors by Mn Alloying Modulated Precipitation Evolution.

Multiscale defects engineering offers a promising strategy for synergistically enhancing the thermoelectric and mechanical properties of thermoelectric semiconductors. However, the specific impact of individual defects, in particular precipitation, on mechanical properties remains ambiguous. In this work, the mechanical and thermoelectric properties of Sn1.03- xMnxTe (x = 0-0.30) semiconductors are systematically studied. Mn-alloying induces dense dislocations and Mn nano-precipitates, resulting in an enhanced compressive strength with x increased to 0.15. Quantitative calculations are performed to assess the strengthening contributions including grain boundary, solid solution, dislocation, and precipitation strengthening. Due to the dominant contribution of precipitation strengthening, the yield strength of the x = 0.10 sample is improved by ≈74.5% in comparison to the Mn-free Sn1.03Te. For x ≥ 0.15, numerous MnTe precipitates lead to a synergistic enhancement of strength-ductility. In addition, multiscale defects induced by Mn alloying can scatter phonons over a wide frequency spectrum. The peak figure of merit ZT of ≈1.3 and an ultralow lattice thermal conductivity of ≈0.35Wm-1K-1 are obtained at 873 K for x = 0.10 and x = 0.30 samples respectively. This work reveals thaprecipitation evolution optimizes the mechanical and thermoelectric properties of Sn1.03- xMnxTe semiconductors, which may hold potential implications for other thermoelectric systems.

Insight into the electronic, optical, thermodynamic, and thermoelectric properties of novel chalcogenides: An ab initio study

AbstractTernary chalcogenides with direct band gaps are remarkable for being used in many optoelectronic applications. We investigated for structural, electronic, optical, and transport characteristics of new Ba2CdCh3 (Ch = S, Se, Te) semiconductors using the full‐potential linearized augmented plane wave (FP‐LAPW) approach. The band structures of these compounds confirm a direct type of band gap. The phonon dispersion plots along with the predicted negative formation energies suggest these compounds to be thermodynamically stable. Additionally, important optical characteristics were computed and thoroughly explained. The different ELF spectra were calculated in which strong peak correlate precisely with plasma resonance. Moreover, we also explored the thermodynamic characteristics of the ternary systems by employing the quasi‐harmonic Debye model. These compounds were also suitable for thermoelectric applications based on the detailed discussion of the computed significant thermoelectric properties. In general, the advancement of various and promising semiconducting devices and their applications will be supported by the present study.

Evolution of magnetotransport properties of Weyl semiconductor Te crystals with different Fermi energy

Evolution of magnetotransport properties of Weyl semiconductor Te crystals with different Fermi energy

Exploring the optoelectronic and thermoelectric nature in Cd-based direct band gap materials: For optoelectronic devices

The direct band gap semiconductors are exceptional for their use as solar cells and in most optoelectronic devices. Using the full-potential linearized augmented plane wave (FP-LAPW) technique, the structural, electronic, optical, and thermoelectric characteristics of novel La2CdX4 (X = S, Se, Te) semiconductors are studied. The electronic band profiles support the density of state calculations and demonstrate a direct band gap nature. These materials appear thermodynamically stable based on the calculated phonon dispersion plots and from their predicted negative formation energy values. Furthermore, the significant optical properties were computed and described extensively. The predicted energy loss function with a few prominent peaks corresponds well with the plasma resonance that occurs at plasma frequency. Based on the reflectivity spectrum, the materials under consideration could be used as UV shielding or anti-reflective coating materials. From the investigation of the calculated significant thermoelectric characteristics, the materials were proven to be appropriate for thermoelectric devices. The current research will support advancement of numerous promising semiconducting technologies and their applications in general.

Design and characterization of novel 2D TlPt2X3 (X = S, Se, Te) semiconductor monolayers for electronic and optoelectronic applications

The energy crisis and environmental issues have stimulated an increasing interest in developing novel materials, such as two-dimensional (2D) materials, with customized photocatalytic and photovoltaic features for sustainable energy production. In this study, we thoroughly investigated the stability, physical characteristics, electronic properties, optical behaviors, and photocatalytic potential of TlPt2X3 (X = S, Se, Te) monolayers (MLs) using state-of-the-art density functional theory calculations at HSE06 and PBE-GGA levels of theory. Our calculations show that these MLs are dynamically, thermally, mechanically, and thermodynamically stable. The elastic constant calculations indicate that these MLs possess high mechanical flexibility owing to their small Young's modulus. The HSE06 approach calculations reveal that the TlPt2S3, TlPt2Se3, and TlPt2Te3 MLs possess band gaps of 1.364 eV (indirect), 1.896 eV (indirect), and 1.174 eV (direct), respectively. The optical characteristics of these MLs demonstrate a wide absorption spectrum that can be activated by visible light, with considerable absorption intensity in the near ultraviolet range. Our findings demonstrate that the TlPt2Se3 (TlPt2Te3) ML exhibits remarkable hydrogen-oxygen (oxygen) evolution performance with an increase (decrease) in pH value, suggesting they can be used for photocatalytic water splitting under visible light. These results provide new directions for the use of these materials in photocatalytic water splitting and optical devices.

Electronic, Elastic, and Thermoelectric Properties of Bulk CdX (X = S, Se, and Te) Binary Semiconductors from First‐Principles Approaches

The electronic, mechanical, and thermoelectric properties of the bulk II–VI binary semiconductors CdX (X = S, Se, and Te) are investigated using first‐principles approaches based on density functional theory (DFT). Calculations for both the zinc‐blende and wurtzite phases of these semiconductors have been performed. The calculated lattice constants, energy band structures, and elastic properties agree with previous theoretical works. According to the results, these semiconductors have low lattice thermal conductivities of about 3–4.5 W m−1 K−1 at room temperature. At high temperatures, p‐type CdX (X = S, Se, and Te) semiconductors outperform n‐type semiconductors in thermoelectric performance.

Defect engineering in ZnIn2X4 (X=S, Se, Te) semiconductors for improved photocatalysis

ZnIn2S4 has emerged as a material of interest for semiconductor-based chalcogenide photocatalysts due to its visible light absorption, chemical and thermal stability, and low cost. However, the photocatalytic activity of ZnIn2S4 is affected by the limited range of visible light absorption and ultrafast recombination of solar light-induced holes and electrons. While previous studies have considered the consequences of metal doping, metal deposition, and vacancy engineering on the photocatalytic activity of ZnIn2S4, a comprehensive understanding of native point defects and how they affect electronic and photocatalytic properties remains elusive. Here, we present a density functional theory (DFT) investigation of defect energetics in ZnIn2X4 (X=S, Se, Te) compounds in both bulk and ultrathin phases. Using both semi-local and hybrid DFT functionals, properties of interest such as the electronic band gap and band edges, optical absorption spectra, and carrier mobilities are first computed for defect-free structures. Although ultrathin ZnIn2S4 shows lower absorption compared to other chalcogenides, it exhibits sufficient overpotential for oxidation and reduction reactions for photocatalytic water splitting. Formation energies of all possible vacancies, self-interstitials, and anti-site substitutional defects are then computed for all structures, as a function of chemical growth conditions, charge state, and Fermi level (EF), which leads to the identification of the lowest energy acceptor and donor type defects and their corresponding shallow or deep level nature. DFT results show that these metal sulfide photocatalysts are prone to ZnIn and InZn anti-site substitutions, which pin the equilibrium EF close to the conduction band edge, indicative of n-type conductivity. While ZnIn does not create deep defect levels in ZnIn2X4, most of the stable native defects do create deep levels, which could adversely affect solar absorption. Finally, we report the influence of defects on the photocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on ultrathin ZnIn2X4. Our results suggest that a metal interstitial defect could substantially boost HER and OER on the surface of ultrathin ZnIn2X4. Overall, this systematic first principles investigation can help drive the experimental design and defect engineering of ZnIn2X4 compounds for a variety of photocatalytic applications.

Exploring the electronic, optical, and thermometric properties of novel AlCuX2 (X = S, Se, Te) semiconductors: a first-principles study

Exploring the electronic, optical, and thermometric properties of novel AlCuX2 (X = S, Se, Te) semiconductors: a first-principles study

Semiconductor Characterization by Terahertz Excitation Spectroscopy.

Surfaces of semiconducting materials excited by femtosecond laser pulses emit electromagnetic waves in the terahertz (THz) frequency range, which by definition is the 0.1-10 THz region. The nature of terahertz radiation pulses is, in the majority of cases, explained by the appearance of ultrafast photocurrents. THz pulse duration is comparable with the photocarrier momentum relaxation time, thus such hot-carrier effects as the velocity overshoot, ballistic carrier motion, and optical carrier alignment must be taken into consideration when explaining experimental observations of terahertz emission. Novel commercially available tools such as optical parametric amplifiers that are capable of generating femtosecond optical pulses within a wide spectral range allow performing new unique experiments. By exciting semiconductor surfaces with various photon energies, it is possible to look into the ultrafast processes taking place at different electron energy levels of the investigated materials. The experimental technique known as the THz excitation spectroscopy (TES) can be used as a contactless method to study the band structure and investigate the ultrafast processes of various technologically important materials. A recent decade of investigations with the THz excitation spectroscopy method is reviewed in this article. TES experiments performed on the common bulk A3B5 compounds such as the wide-gap GaAs, and narrow-gap InAs and InSb, as well as Ge, Te, GaSe and other bulk semiconductors are reviewed. Finally, the results obtained by this non-contact technique on low-dimensional materials such as ultrathin mono-elemental Bi films, InAs, InGaAs, and GaAs nanowires are also presented.

Electronic properties of graphene/CdX (X=S, Se, and Te) semiconductor heterostructure and a proposal of all-optical injection and detection of electron spins in graphene

Graphene was predicted to have a long spin relaxation time in the range of microseconds to milliseconds due to its weak spin-orbit coupling and hyperfine interaction. However, very short spin relaxation times were measured experimentally on the order of nanoseconds. Magnetic proximity effect from spin valves were considered strongly to influence the electronic and spin properties in graphene. Here, a graphene/nonmagnetic semiconductor CdX heterostructure is proposed to eliminate the magnetic effect and to fulfill optical injection of spin polarization. Based on the first-principles calculation within the density functional theory, we perform a systematic study on the structural, electronic properties and band structures of the heterostructures, and find that graphene on CdX (X = S, Se and Te) slabs preserves its linear Dirac band structure within the bandgap of CdX, and a built-in electric field occurs near the interface. The built-in electric field drives spin polarized electrons into graphene preferably. An optical detection scheme of spin relaxation time of graphene is proposed based on Faraday and Hanle effects. • A graphene/nonmagnetic semiconductor heterostructure constructed to eliminate strong magnetic effects on spin relaxation time of electrons in graphene. • First-principles calculations reveal Graphene on CdX (X = S, Se and Te) slabs preserves its linear Dirac band structure which locates within the bandgap of CdX. • A built-in electric field exists within interface, which favor spin polarized electrons transported into graphene. • A new scheme of all-optical injection and detection of electron spin is proposed to measure true long spin relaxation time of graphene.

Resistive Switching in Ag2Te Semiconductor Modulated by Ag+‐Ion Diffusion and Phase Transition

AbstractMemristors are considered to be the fourth circuit element and have great potential in areas like logic operations, information storage, and neuromorphic computing. The functional material in a memristor, which has a nonlinear resistance, is the key component to be developed. Herein, resistive switching is demonstrated and the structural evolutions in Ag2Te are examined under an external electric field. It is shown that the electroresistance effect is originating from an electronically triggered phase transition together with directional Ag+‐ion diffusion. Using in situ transmission electron microscopy, the phase transition from the monoclinic α‐Ag2Te into the face‐centered cubic b‐Ag2Te, accompanied by a change in resistance, is directly observed. Diffusion of Ag+‐ions modulates the localized density of Ag+‐ion vacancies, leading to a change in electrical conductivity and influences the threshold voltage to trigger the phase transition. During the electric field‐driven phase transition, the spontaneous and localized multiple polarizations from the low‐symmetry α‐Ag2Te (referring to an antiferroelectric structure) are vanishing in the cubic b‐Ag2Te (referring to a paraelectric structure). The abrupt resistance change of thin Ag2Te caused by the phase transition and modulated by the applied electric field demonstrates its great potential as functional material in volatile memory and memristors with a low‐energy consumption.

Neuromorphic Computing

In the face of increasingly large computational demands and the impending halt to Moore's law, the semiconductor industry has been forced to re-evaluate the traditional computing paradism. Central to this re-evaluation has been the novel development of neuromorphic computing - an approach that, at its core, seeks to replicate the brain in silicon. Despite challenges on the algorithmic front, neuromorphic computing promises a massively parallel, efficicient, and scalable computational solution with large implications on the daily lives of consumers. The future of the technology, however, is uncertain. With the rise of high performance and Quantum computing as promising alternatives, te semiconductor industry at large must consider the extent to which neuromorphic computing can emerge as a viable and feasible solution in the coming years. It is vital, therefore, to understand the theoretical underpinnings of the neuromorphic approach and predict the likelihood of its implementation within the next decade

Optical Properties and Lattice Dynamics of Pure and S‐Alloyed Cu–Zn–Sn–Te Semiconductors: First‐Principles Calculations and Raman Scattering

The electronic band structure, the optical properties, and the lattice dynamics of the quaternary Cu2ZnSnTe4 (CZTTe) semiconductor with kesterite crystallographic structure are calculated within first principles. The analysis of the phonon partial density of states shows that the highest frequency phonon mode involves mostly heavy Sn and Te atoms due to their exceptionally strong bonding. Experimental Raman spectra of Cu–Zn–Sn–Te nanocrystals, prepared by an aqueous colloidal synthesis, reveal a single characteristic line and its higher order overtones due to specific resonant conditions. In the case of Cu–Zn–Sn–(Te–S) alloy nanoparticles, other Raman features, related to Sn–S vibrations, appear in the spectra indicating a two‐mode type of transformation of their vibrational spectra. The effect of sulfur incorporation on the Te‐related frequency is opposite to the effect observed for the Se‐related frequency in CZTSSe alloys.

New two-dimensional Ge–Sb–Te semiconductors with high photovoltaic performance for solar energy conversion

Three new stable semiconducting Ge–Sb–Te monolayers exhibit high visible-light absorbance (105–106 cm−1) and photovoltaic efficiency (26–30% at 0.1 μm), considerably larger than the currently dominant commercial photovoltaic semiconductor Si.