Impurities In Semiconductors Research Articles

CURRENT OSCILLATIONS IN IMPURITY SEMICONDUCTORS WITH BOTH SIGNS OF CURRENT CARRIERS IN THE PRESENCE OF AN EXTERNAL ELECTRIC FIELD, A TEMPERATURE GRADIENT AND A WEAK MAGNETIC FIELD (μ_± H<<C)

It is theoretically shown for the first time that in an external electric and weak magnetic fields, when there is a temperature gradient, an impurity semiconductor radiates energy from itself with a certain frequency. The values of the frequency of current oscillations and the limit of change of the external electric field are found. It is shown that the resistance in the medium has only ohmic character. It is stated that in the above semiconductor, when the concentration of electrons and holes are determined from the obtained expression in theory, the injection of contacts plays a major role for the appearance of the indicated current oscillation in the circuit.

Enhancing ECU identification security in CAN networks using distortion modeling and neural networks

A novel technique for electronic control unit (ECU) identification is proposed in this study to address security vulnerabilities of the controller area network (CAN) protocol. The reliable ECU identification has the potential to prevent spoofing attacks launched over the CAN due to the lack of message authentication. In this regard, we model the ECU-specific random distortion caused by the imperfections in the digital-to-analog converter and semiconductor impurities in the transmitting ECU for fingerprinting. Afterward, a 4-layered artificial neural network (ANN) is trained on the feature set to identify the transmitting ECU and the corresponding ECU pin. The ECU-pin identification is also a novel contribution of this study and can be used to prevent voltage-based attacks. We have evaluated our method using ANNs over a dataset generated from 7 ECUs with 6 pins, each having 185 records, and 40 records for each pin. The performance evaluation against state-of-the-art methods revealed that the proposed method achieved 99.4% accuracy for ECU identification and 96.7% accuracy for pin identification, which signifies the reliability of the proposed approach.

Inert Gas Element as Active Infrared‐Absorption Source and Donor in Silicon for Forbidden‐Wavelength Sensing

AbstractIntrinsic silicon (Si) is forbidden for infrared (IR) sensing at the communication wavelength like 1.31 or 1.55 µm due to the well‐known bandgap limitation. In this work, an unexpected physical picture of using argon (Ar) is identified, which is usually inert to the surrounding chemical environment and used as a protective agent in semiconductor processing, to overcome the IR‐sensing‐forbidden problem in Si. Here, it is shown by an analysis of a dynamic secondary ion mass spectrometer that such a Si, when exposed to laser pulse in Ar gas, can contain a very high dose of Ar up to 1020 cm−3 even after 1300 days. First‐principles calculations, molecular dynamics, and Hall effect measurements reveal that, due to both steric and dynamic repulsions by Ar orbitals to Si dangling bonds, the Ar‐filled‐vacancy produces a much wider defect band inside the gap, which is not only responsible for strong infrared absorption, but also causes a significant increase in n‐type conductivity, both in line with experiments. The study proves that originally inert elements in fact can act as active impurities in semiconductors for advanced applications, which updates the current knowledge of defect physics.

Rational design of efficient defect-based quantum emitters

Single-photon emitters are an essential component of quantum networks, and defects or impurities in semiconductors are a promising platform to realize such quantum emitters. Here, we present a model that encapsulates the essential physics of coupling to phonons, which governs the behavior of real single-photon emitters, and critically evaluate several approximations that are commonly utilized. Emission in the telecom wavelength range is highly desirable, but our model shows that nonradiative processes are greatly enhanced at these low photon energies, leading to a decrease in efficiency. Our results suggest that reducing the phonon frequency is a fruitful avenue to enhance the efficiency.

Hole and positron interaction with vacancies and p-type dopants in epitaxially grown silicon

The concentration of vacancies and impurities in semiconductors plays a crucial role in determining their electrical, optical, and thermal properties. This study aims to clarify the nature of the interaction between positrons and ionized p-type impurities, emphasizing the similarities they share with the interaction between holes and this type of impurity. An overall strategy for investigating defects in semiconductor crystals that exhibit a combination of vacancies and p-type impurities is presented. By using positron annihilation spectroscopy, in particular, Doppler broadening of the annihilation radiation, we quantify the concentration of vacancies in epitaxial Si crystals grown by low-energy plasma-enhanced chemical vapor deposition. The vacancy number densities that we find are (1.2 ± 1.0) × 1017 cm−3 and (3.2 ± 1.5) × 1020 cm−3 for growth rates of 0.27 and 4.9 nm/s, respectively. Subsequent extended annealing of the Si samples effectively reduces the vacancy density below the sensitivity threshold of the positron technique. Secondary ion mass spectrometry indicates that the boron doping remains unaffected during the annealing treatment intended for vacancy removal. This study provides valuable insights into the intricate interplay between vacancies and ionized impurities with positrons in semiconductor crystals. The obtained results contribute to advance the control and understanding of material properties in heterostructures by emphasizing the significance of managing vacancy and dopant concentrations.

Unraveling the crucial role of trace oxygen in organic semiconductors

Optoelectronic properties of semiconductors are significantly modified by impurities at trace level. Oxygen, a prevalent impurity in organic semiconductors (OSCs), has long been considered charge-carrier traps, leading to mobility degradation and stability problems. However, this understanding relies on the conventional deoxygenation methods, by which oxygen residues in OSCs are inevitable. It implies that the current understanding is questionable. Here, we develop a non-destructive deoxygenation method (i.e., de-doping) for OSCs by a soft plasma treatment, and thus reveal that trace oxygen significantly pre-empties the donor-like traps in OSCs, which is the origin of p-type characteristics exhibited by the majority of these materials. This insight is completely opposite to the previously reported carrier trapping and can clarify some previously unexplained organic electronics phenomena. Furthermore, the de-doping results in the disappearance of p-type behaviors and significant increase of n-type properties, while re-doping (under light irradiation in O2) can controllably reverse the process. Benefiting from this, the key electronic characteristics (e.g., polarity, conductivity, threshold voltage, and mobility) can be precisely modulated in a nondestructive way, expanding the explorable property space for all known OSC materials.

Magnetoresistance ratio in magnetic tunnel junction with silicon diffused MgO barrier

We demonstrated a magnetic tunnel junction (MTJ) consisting of Fe/MgO-Si-MgO/Fe. Si layer was deposited at room temperature and at 700 °C; when deposited at 700 °C, Si diffused into the MgO layer. The MTJ with silicon deposited at 700 °C attained high MR ratios of up to 38.7 and 2.9% at t Si = 0.19 and 1.3 nm, respectively. Low-temperature measurements established that the temperature dependence of the MR ratio and resistance between MTJs with and without diffused silicon are significantly different. This behavior confirms that the Si-MgO channel acts as an impurity semiconductor in the MTJ.

Maximum Hopping Direct Current Conductivity via Hydrogen-like Impurities in Semiconductors

Maximum Hopping Direct Current Conductivity via Hydrogen-like Impurities in Semiconductors

Features of the Electrical Properties of Limited Diffusion Semiconductors in Contact Measurements

The purpose of this work is to study the features of the electrical properties of bounded semiconductors, as well as the effect of the inhomogeneous distribution of impurities in anisotropic semiconductors on the structure of electric fields with standard methods of contact measurements.Diffusion and ion-doped semiconductor structures, as well as composite structures with misalignment of film and substrate lattices, are currently a promising class of materials in micro- and nanoelectronics. The introduction of an impurity into a semiconductor crystal sample changes its electrical properties, which makes it possible to reduce the size of individual components of the chip, while maintaining or increasing their power.Methods. The results of the work are based on the known dependences of the distributions of impurities during diffusion alloying. To calculate the potential distribution, the Fourier method was used, which made it possible to solve the Poisson Equation with Neumann boundary conditions without approximations. The mathematical package MathCad was used to analyze the obtained expressions characterizing electric fields in inhomogeneous semiconductors.Results. A technique for solving the boundary value problem for the potential in bounded diffusion semiconductors is presented. Expressions in the form of series of analytical functions for the distribution of electric potential in conducting anisotropic structures are presented. The constructed models make it possible to determine and qualitatively describe the distributions of electric fields during probe measurements and to investigate their structure in diffusion semiconductors. Conclusion. On the basis of computer modeling, the importance of taking into account the parameters of inhomogeneity of conductivity is shown. The effect of concentration of current density lines in diffusion semiconductors is shown and quantified.

(Invited) Universal Alignment of Surface and Bulk Oxygen Levels in Semiconductors

Lattices of most semiconductors have a large density of intrinsic and extrinsic defects which gives rise to effects such as surface Fermi level (EF) pinning, dopant compensation, asymmetrical p versus n-doping, and device degradation. Oxygen and hydrogen are the two most important impurities in semiconductors because of their ubiquitous presence in growth and device processing environments and consequently their incorporation strongly influences electronic and electrical properties. Therefore, a deeper understanding of the interaction of these species with the semiconductor surface and bulk defects is necessary for enabling the development of devices based on them such as photovoltaic and photocatalytic systems, fuel cells, and many others. Analysis of the reported surface work function values and the substitutional bulk O-defect energies show that the surface Fermi level of position in a broad range of group IV, III-V, II-VI, and I-III-VI2 semiconductors with physisorbed O2 lies universally at approximately -5.1 eV below the vacuum level. Similarly, results show that the energy of the bulk substitutional O-related amphoteric defects incorporated during crystal growth also has a universal energy of ~ -5.0 eV with respect to the vacuum level for most of the investigated semiconductors. It is shown that the process of ‘surface transfer doping’ that involves an adsorbed nanoscale water film on the semiconductor surface is likely responsible for the universal alignment of oxygen levels. Figure 1

Trap-Assisted Auger-Meitner Recombination from First Principles.

Trap-assisted nonradiative recombination is known to limit the efficiency of optoelectronic devices, but the conventional multiphonon emission (MPE) process fails to explain the observed loss in wide-band-gap materials. Here, we highlight the role of trap-assisted Auger-Meitner (TAAM) recombination and present a first-principles methodology to determine TAAM rates due to defects or impurities in semiconductors or insulators. We assess the impact on efficiency of light emitters in a recombination cycle that may include both TAAM and carrier capture via MPE. We apply the formalism to the technologically relevant case study of a calcium impurity in InGaN, where a Shockley-Read-Hall recombination cycle involving MPE alone cannot explain the experimentally observed nonradiative loss. We find that, for band gaps larger than 2.5eV, the inclusion of TAAM results in recombination rates that are orders of magnitude larger than recombination rates based on MPE alone, demonstrating that TAAM can be a dominant nonradiative process in wide-band-gap materials. Our computational formalism is general and can be applied to the calculation of TAAM rates in any semiconducting or insulating material.

Photoexcitation of planar Wannier excitons by twisted photons

Photoexcitation of planar Wannier excitons by twisted photons in thin semiconductor films is investigated. The excitons are assumed to be already created. The explicit general formulas for transition probabilities between exciton states are derived. The selection rules for the projection of the total angular momentum are obtained. As examples, the Coulomb and Rytova–Keldysh electron–hole interaction potentials are considered. The use of planar excitons as a pure on-chip source of twisted photons is discussed. The formulas obtained also describe photoexcitation of states of electrons and holes bound to charged impurities in planar semiconductors.

Characterization of boron-doped single-crystal diamond by electrophysical methods (review)

A critical analysis of the existing methods of controlling the concentration of impurity and majority charge carriers in wide bandgap semiconductors and the issues of improvement of modern diagnostics of the main electrophysical properties of single-crystal diamond are considered based on the results of our studies and the works of other authors. It was found that independent assessment of impurity concentration and concentration of free charge carriers is of fundamental importance for semiconductor diamond due to very low (less than 1%) degree of ionization of the introduced impurity. The advantages and prospects of admittance spectroscopy as a diagnostic method for ultrawide bandgap semiconductors are shown and solutions aimed at the correct interpretation of the experimental data are proposed. The high ionization energy of boron impurity in diamond (370 meV) results in a strong frequency dispersion of the measured barrier capacitance. It is shown that under disturbance of quasi-static conditions in capacitance-voltage measurements, low frequencies and high temperatures should be used for correct assessment of the charge carrier concentration. The results of electrophysical studies are compared with traditional measurements of impurity concentration in diamond by optical methods. A decrease of hole activation energy from the boron impurity level from 325 to 100 meV was found upon increasing the boron concentration NA from 2·1016 to 4·1019 cm-3. The transition to the hopping mechanism of conductivity within the impurity (acceptor) band with thermal activation energy of 10-20 meV was registered for NA≥5·1018 cm-3 at temperatures of 120-150 K. Keywords: single-crystal diamond, boron impurity, charge carrier concentration, activation energy, admittance spectroscopy, capacitance-voltage measurements.

Identification of carbon location in p-type GaN: Synchrotron x-ray absorption spectroscopy and theory

Identifying atomic configurations of impurities in semiconductors is of fundamental interest and practical importance in designing electronic and optoelectronic devices. C impurity acting as one of the most common impurities in GaN, it is believed for a long time that it substitutes at Ga site forming CGa with +1 charge-state in p-type GaN, while it substitutes at N site forming CN with -1 charge-state in n-type GaN. However, by combining x-ray absorption spectroscopy and first-principles simulations, we observed that C is mainly occupying the N site rather than the Ga one in p-GaN. We further reveal that this is due to an H-induced EF-tuning effect. During growth, the existing H can passivate Mg dopants and upshifts the EF to the upper region of bandgap, leading to the CN formation. After the p-type activation by annealing out H, although the EF is pushed back close to the valence band maximum, whereas the extremely large kinetic barrier can prevent the migration of C from the metastable CN site to ground-state CGa site, hence stabilizing the CN configuration. Additionally, the CN with neutral charge-state (CN0) in the p-GaN is further observed. Therefore, the real C-related hole-killer in p-type GaN could be CN rather than the commonly expected CGa. Our work not only offers the unambiguous evidence for the C defect formation in p-GaN but also contributes significantly to an in-depth understanding of the C-related hole-killers and their critical role on electrical and optoelectrical properties of p-GaN and even p-AlGaN.

Hole-Doping to a Cu(I)-Based Semiconductor with an Isovalent Cation: Utilizing a Complex Defect as a Shallow Acceptor.

p-Type doping in Cu(I)-based semiconductors is pivotal for solar cell photoabsorbers and hole transport materials to improve the device performance. Impurity doping is a fundamental technology to overcome the intrinsic limits of hole concentration controlled by native defects. Here, we report that alkali metal impurities are prominent p-type dopants for the Cu(I)-based cation-deficient hole conductors. When the size mismatch with Cu+ in the host lattice is increased, these isovalent impurities are preferentially located at interstitial positions to interact with the constituent Cu cations, forming stable impurity-defect complexes. We demonstrate that the Cs impurity in γ-CuI semiconductors enhances hole concentration controllability for single crystals and thin films in the range of 1013-1019 cm-3. First-principles calculations indicate that the Cs impurity forms impurity-defect complexes that act as shallow acceptors leading to the increased p-type conductivity. This isovalent doping provides an approach for controlled doping into cation-deficient semiconductors through an interaction of impurities with native defects.

Atomic-scale visualization of the p−d hybridization in III-V semiconductor surfaces doped with transition metal impurities

p-d hybridization of transition metal impurities in a semiconductor host is the mechanism that couples valence-band electrons and localized spins. We use scanning tunneling microscopy and spectroscopy combined with density functional theory to probe at the atomic scale hybridization of Cr single impurities with GaAs host. Combining spatial density of states mapping and in-gap states spectroscopy of the Cr substituted at the surface of the semiconductor, we give a detailed picture of the spatial extension and the electronic structure of the strongly anisotropic wave function of Cr on GaAs(110). First principles calculations allow to identify electronic character and origin of each states and show that the main resonance peaks and the wave function with "drop-eyes" lobes experimentally observed for 3d metal impurities in III-V semiconductor are direct local evidences of the p-d hybridization.

Visualization of quantized vortex reconnection enabled by laser ablation.

Impurity injection into superfluid helium is a simple and appealing method with diverse applications, including high-precision spectroscopy, quantum computing with surface electrons, nano/micromaterial synthesis, and flow visualization. Quantized vortices play a major role in the interaction between superfluid helium and light impurities. However, the basic principle governing this interaction is still unclear for dense (high mass density and refractive index) materials, such as semiconductor and metal impurities. Here, we provide experimental evidence of the dense silicon nanoparticle attraction to the quantized vortex cores. We prepared the silicon nanoparticles via in situ laser ablation. Following laser ablation, we observed that the silicon nanoparticles formed curved filament–like structures, indicative of quantized vortex cores. We also observed that two accidentally intersecting quantized vortices exchanged their parts, a phenomenon called quantized vortex reconnection. This behavior closely matches the dynamical scaling of reconnections. Our results provide a previously unexplored method for visualizing and studying impurity-quantized vortex interactions.

A hybrid density functional design of intermediate band semiconductor for photovoltaic application based on group IV elements (Si, Ge, Sn, and Pb)-doped CdIn2S4

The CdIn2S4 semiconductor is considered a potential host for the implementation of intermediate band solar cells due to its ideal bandgap value and excellent photoelectric property. In this paper, the electronic structures of group IV elements (Si, Ge, Sn, and Pb)-doped CdIn2S4 have been investigated by using hybrid density functional calculations. In the case of Ge, Sn, and Pb doping, an isolated and partially occupied intermediated band with delocalized characteristics could be created in the bandgap of the host. The results of the projected density of states reveal that the intermediated band is derived from the hybridization between the S-3p and dopant-ns states. Thanks to the assistance of the impurity band, the optical absorption ability of the intermediate band semiconductor is greatly enhanced. Based on the detailed balance theory, the theoretical efficiencies of intermediate band solar cells made by Ge- and Pb-doped CdIn2S4 are estimated to be 45.0% and 49.2%, respectively, which are superior to the Shockley and Queisser limit (40.7%) of a single junction photovoltaic device. Moreover, the experimental synthesis of these impurity semiconductors is relatively feasible because substitutional doping at the octahedral position is energetically favorable. These findings would be helpful to the development of a high-efficiency intermediate band solar cell.

Machine learning for impurity charge-state transition levels in semiconductors from elemental properties using multi-fidelity datasets.

Quantifying charge-state transition energy levels of impurities in semiconductors is critical to understanding and engineering their optoelectronic properties for applications ranging from solar photovoltaics to infrared lasers. While these transition levels can be measured and calculated accurately, such efforts are time-consuming and more rapid prediction methods would be beneficial. Here, we significantly reduce the time typically required to predict impurity transition levels using multi-fidelity datasets and a machine learning approach employing features based on elemental properties and impurity positions. We use transition levels obtained from low-fidelity (i.e., local-density approximation or generalized gradient approximation) density functional theory (DFT) calculations, corrected using a recently proposed modified band alignment scheme, which well-approximates transition levels from high-fidelity DFT (i.e., hybrid HSE06). The model fit to the large multi-fidelity database shows improved accuracy compared to the models trained on the more limited high-fidelity values. Crucially, in our approach, when using the multi-fidelity data, high-fidelity values are not required for model training, significantly reducing the computational cost required for training the model. Our machine learning model of transition levels has a root mean squared (mean absolute) error of 0.36 (0.27)eV vs high-fidelity hybrid functional values when averaged over 14 semiconductor systems from the II-VI and III-V families. As a guide for use on other systems, we assessed the model on simulated data to show the expected accuracy level as a function of bandgap for new materials of interest. Finally, we use the model to predict a complete space of impurity charge-state transition levels in all zinc blende III-V and II-VI systems.

Template‐Guided C8‐BTBT/MAPbBr3/C8‐BTBT Heterostructures for Broadband Bipolar Phototransistors

AbstractBipolar junction transistor (BJT) has had an unprecedented impact on the electronic industry and helped to usher in the digital revolution prominently. However, the critical part of BJT, p–n junction, is formed by carefully incorporating substitutional impurities in traditional bulk semiconductors and it is difficult to implement in nanostructured device. In this work, a floating‐base BJT device is demonstrated by growing C8‐BTBT/MAPbBr3/C8‐BTBT PNP heterostructure in liquid phase. Growth of two semiconductor microwires into a crisscross heterojunction is achieved through template‐guided printing and antisolvent crystallization method. The proof‐of‐concept phototransistor demonstrates broadband light absorption from ultraviolet (UV) to visible spectral region, which exhibits enhanced photoresponsivities of 1.28 A W–1 to UV and 0.425 A W–1 to visible light, respectively. In addition, the improved photoelectric amplification behavior of C8‐BTBT/MAPbBr3/C8‐BTBT phototransistor is observed by comparing with the performance of C8‐BTBT/MAPbBr3 two‐component photodiode. The maximal gain can reach up to ≈600 and can be maintained ≥200 at the positive bias. The device provides new attractive prospects in the investigation of integrated circuits based on micro‐structured semiconductors.