N-doped Semiconductor Research Articles

Carrier-Carrier Repulsion Limits the Conductivity of N-Doped Organic Semiconductors.

Molecular doping is a key strategy to enhance the electrical conductivity of organic semiconductors. Typically, the electrical conductivity shows a maximum value upon increased doping, after which the conductivity decreases. This decrease in conductivity is commonly attributed to unfavorable changes in the morphology. However, in recent simulation work, has shown, that the conductivity-at high doping-is instead limited by electron-electron repulsion rather than by morphology, at least for some material combinations. Based on the simulations, this limitation is expected to show up in the dependence of the Seebeck coefficient versus carrier density: the Seebeck coefficient will follow Heike's formula if carrier-carrier repulsion limits the conductivity. Here, the electrical conductivity and Seebeck coefficient are measured as a function of doping for a series of n-type organic semiconductors. Additionally, the resulting carrier density is measured using metal-insulator-semiconductor diodes, which link dopant loading and the number of charge carriers. At high carrier densities, the Seebeck coefficient indeed follows Heike's formula, confirming that the conductivity is limited by carrier-carrier repulsion rather than by morphological effects. This study shows that current models of hopping transport in organic semiconductors may be incomplete. As a result, this study offers novel insights in the design of organic semiconductors.

Theory of Tribovoltaics: Direct Current Generation at a p - n Semiconductor Interface

A simple theory of tribovoltaics is proposed by using a quantum mechanical model of energy release due to sliding-induced bonding between the surfaces of a p-doped semiconductor and a n-doped semiconductor. The energy release in forming a bond may lead to the excitation of electron-hole pairs at the p-n semiconductor interface if the released energy is higher than the effective band gap at the semiconductor interface. An expression for the generated current as a function of the relative sliding speed between the p and n sides is suggested and used to model current transport by solving the complete set of drift-diffusion equations with appropriate boundary and initial conditions. Analytical results are obtained and verified numerically using the finite-element-method software. It is shown that since the typical time period associated with periodic sliding is many orders of magnitude higher than the carrier lifetimes, the time-dependent variations in the electron and hole concentrations and the current density follow the time variation of the sliding speed. Since the electron-hole pair generation occurs near the semiconductor interface only, the current density is shown to be constant as a function of position even if the sliding speed changes in time. Published by the American Physical Society 2024

A fluorinated greenhouse gas sensor based on N-doped tin oxide materials

A novel N-doped tin oxide semiconductor metal oxide sensor has been successfully fabricated for fluorinated greenhouse gas sensing.

Influence of nonlinear semiconductor layer on optical properties in one-dimensional photonic crystals

In this paper, an attempt has been made to investigate a one-dimensional photonic crystal containing N-doped germanium semiconductor as a nonlinear defect layer with an intensity-dependent refractive index, silica (SiO2) and zinc selenide (ZnSe) as crystal cells. Bistability of the TE polarization of the transmission spectrum due to the nonlinear property of the defect layer is investigated by the transfer matrix method (TMM). The refractive index of the germanium nonlinear semiconductor layer is simultaneously depending on the doping density and the intensity of the irradiated light. The changes in both factors are investigated. The impact on the transmission spectrum of the bistability threshold due to the change in the thickness of the defect layer, the thickness of other layers of crystal cells, and the angle of incident light are investigated. The nonlinear effect caused by light intensity as well as doped density effect on the germanium nonlinear semiconductor medium is used simultaneously. As a result, the nonlinear effect caused by the light intensity to create bistability is more than the doping density.

Electronic properties of diamond semiconductor materials: based on response surface model

Abstract Diamond, a wide bandgap semiconductor material, has excellent physicochemical properties. It has great potential for application in high temperature, high frequency, high power electronic devices and other high technology fields. In order to study the electronic properties of diamond more precisely, an AM-response surface model is developed in this paper to investigate the electronic structures of diamond, P-doped diamond and N-doped diamond surfaces in depth. It is shown that there are three forms of charge states in the single vacancy on the diamond surface. When E=0 V, the negative charge energy level is -0.5 mV, the positive charge is 1 mV, and the zero level remains 0. And its energy level is unstable. In contrast, the double vacancy charge on the diamond surface varies depending on the valence band taken by E, and only one charge state exists. When E<0, the diamond surface vacant electron nature is negative charge state. When E>0, it is positive charge energy level. The electronic properties of the P-doped diamond semiconductor material are calculated to have a constant positive charge (1 mV). The electronic property of N-doped diamond semiconductor material is constant negative charge (-1mV).

Strong Coupling in Infrared Plasmonic Cavities.

Controlling molecular spectroscopy and even chemical behavior in a cavity environment is a subject of intense experimental and theoretical interest. In Fabry-Pérot cavities, strong (radiation-matter) coupling phenomena without an intense radiation field often rely on the number of chromophore molecules collectively interacting with a cavity mode. For plasmonic cavities, the cavity field-matter coupling can be strong enough to manifest strong coupling involving even a single molecule. To this end, infrared plasmonic cavities can be particularly useful in understanding vibrational strong coupling. Here we present a procedure for estimating the radiation-matter coupling and, equivalently, the mode volume as well as the mode lifetime and quality factor for plasmonic cavities of arbitrary shapes and use it to estimate these quantities for infrared cavities of two particularly relevant geometries comprising several n-doped semiconductors. Our calculations demonstrate very high field confinement and low mode volumes of these cavities despite having relatively low quality factors, which is often the case for plasmonic cavities.

Behavior of N-Doped TiO2 and N-Doped ZnO in Photocatalytic Azo Dye Degradation under UV and Visible Light Irradiation: A Preliminary Investigation

N-doped TiO2 (N-TiO2) and N-doped ZnO (N-ZnO) were synthesized utilizing ammonia as a dopant source. The chemico-physical characteristics of synthesized samples were studied by Raman spectroscopy, X-ray diffraction, SEM analysis, N2 adsorption–desorption at −196 °C, and diffuse reflectance spectroscopy. Compared to undoped samples, the introduction of nitrogen in the semiconductor lattice resulted in a shift of band-gap energy to a lower value: 3.0 eV for N-ZnO and 2.35 eV for N-TiO2. The photocatalysts were tested for the degradation of Eriochrome Black T (EBT), which was selected as a model azo dye. Both N-doped semiconductors evidenced an improvement in photocatalytic activity under visible light irradiation (62% and 20% EBT discoloration for N-TiO2 and N-ZnO, respectively) in comparison with the undoped samples, which were inactive in the presence of visible light. Different behavior was observed under UV irradiation. Whereas N-TiO2 was more photoactive than commercial undoped TiO2, the introduction of nitrogen in ZnO wurtzite resulted in a drastic reduction in photocatalytic activity, with only 45% EBT discoloration compared to total color removal obtained with the commercial ZnO sample, suggesting intrinsic limitations for doping of this class of semiconductors.

Properties of the defect mode of a ternary photonic crystal having an n-doped semiconductor as a defect layer: TE case

In this work, a ternary photonic crystal having an n-doped semiconductor as a defect layer is considered. Tunable properties of the transmission spectra are investigated for TE waves. The three layers of the proposed photonic crystal are Si, Bi4Ge3O12 and SiO2 and the defect layer is n-GaAs. The transmission properties and defect mode of the structure may be controlled by using the doping rate, applied magnetic field and width of the n-GaAs layer. The defect layer width is found the most efficient factor among these three factors. The analysis is performed in the near-infrared spectral region. The proposed structure can be used to construct filters with narrowband transmission peaks.

Urbach Rule in the Red-Shifted Absorption Edge of PET Films Irradiated with Swift Heavy Ions.

This paper presents a new analysis of the experimental transmission spectra of polyethylene terephthalate (PET) films before and after irradiation with swift heavy ions (SHI) films, as reported previously by the authors. It is shown that the absorption edge red shift for irradiated films contains two regions of exponential form, one of which is located in the UV region and the other at lower energy, mainly in the visible part of the spectrum. The behaviour of the transmission curves under different irradiating fluences demonstrates that these two regions reflect respectively the electron-enriched core of the latent track and its electron-depleted peripheral halo. The focal point method yields a bandgap energy of 4.1 eV for the electron-enriched core of the latent track, which is similar to n-doped semiconductors, and a bandgap of about 1.3–1.5 eV for the electron-depleted halo, similar to p-doped semiconductors. The boundary between the latent track cores and halos corresponds to a conventional semiconductor p-n junction. The values of the characteristic Urbach energy determined from experimental data correspond to the nonradiative transition energy between the excited singlet and triplet levels of benzene-carboxyl complexes in repeat units of the PET chain molecule. A parallel is drawn between the SHI-induced redistribution of electrons held in structural traps in the PET film and chemical redox reactions, which involve the redistribution of electrons in chemical bonds. It is suggested that alkali etching triggers the release of excess electrons in the latent track cores, which act as a catalyst for the fragmentation of PET chain molecules along the latent tracks of the SHI irradiation.

Nitrogen Doped Titanium Dioxide (N-TiO2): Synopsis of Synthesis Methodologies, Doping Mechanisms, Property Evaluation and Visible Light Photocatalytic Applications

Titanium dioxide (TiO2) is one of the stable and potential metal oxide semiconductor nanomaterials with flexible properties which allows them to be used in a variety of applications (i.e., environmental remediation, energy storage and production, and also as a pigment in personal care products, etc.). However, its low surface area, poor adsorption capacity and high bandgap energy (~3.2 eV) prevents its full potency. Especially, TiO2 with high bandgap (~3.2 eV) reduces its visible light absorption capacity and catalytic efficiency. Various modification processes (i.e., metal and non-metal doping, composite materials (mixed metal oxide, high surface area adsorbents), and dye sensitization etc.) have been accomplished for stimulating the characteristics of TiO2 and the associated catalytic efficiency. Among the modifications, the non-metal doping process in TiO2, specifically nitrogen doping, is one of the efficient dopants for enhancing the photocatalytic efficiency of TiO2 in the presence of visible light irradiation. However, the morphology of TiO2, structural changes in TiO2 during N-doping, properties (e.g., morphology and electronic) of N-doped TiO2 and also reaction operational parameters (e.g., doping concentration) hold a greater impact for enhancing the photocatalytic properties of TiO2 either positively or negatively. Furthermore, the synthesis methodologies have a major influence on the synthesis of stable N-TiO2 with pronounced photocatalytic efficiencies. Nevertheless, the methodologies for highly stable N-TiO2 synthesis, properties evaluation and their correlation with photocatalytic efficiencies are still not appropriately stabilized to accomplish the commercial utilization of N-TiO2. Therefore, this review article focuses on the synopsis of various synthesis methodologies and either their efficiencies or inefficiencies, the mechanism involved in the doping processes, changes in the structural, electronic and morphological properties observed due to the N-doping along with the photocatalytic capacity. Furthermore, the opportunities, challenges and future requirements linked to the development of durable N-doped TiO2-based semiconductor nanomaterials for efficient catalytic performance is also represented.

Microscopic Insights into Charge Formation and Energetics in n-Doped Organic Semiconductors

Microscopic Insights into Charge Formation and Energetics in n-Doped Organic Semiconductors

Efficient photocatalytic removal of four endocrine-disrupting compounds using N-doped BiOBr catalyst under UV-Vis radiation

A mixture of four endocrine-disrupting compounds (EDCs [17β-estradiol, 17α-ethinylestradiol, bisphenol A, and 4-tert-octylphenol]) was removed from aqueous solution using the N-doped BiOBr semiconductor (N = 10 and 20 wt%) easily prepared via microwave-assisted solvothermal synthesis. The N20BiOBr semiconductor showed the highest photocatalytic activity achieving the complete degradation of the EDCs, and 53.5% of mineralization in 240 min. Moreover, the toxicity of the mixture was reduced to moderate levels (from 90 to 47.5% of inhibition of the bioluminescence of V. fischeri). The high efficiency of N20BiOBr for EDCs removal was attributed to the increase of the specific surface area and the effective separation of photogenerated charges by effect of N incorporation. The main photogenerated species involved in the degradation of the pollutants were the superoxide radicals (O2•-) and photo-holes (h+), and a possible photocatalytic activation mechanism was proposed where suggests the active participation of oxygen vacancies. Additionally, N20BiOBr demonstrated excellent chemical and photocatalytic stability after four reuse cycles. Therefore, doping BiOBr with N constitutes a suitable and efficient strategy for the photocatalytic removal of a mixture of hazardous pollutants such as EDCs in water, with potential application in tertiary decontamination processes.

Electron-induced nuclear magnetic ordering in n -type semiconductors

Nuclear magnetism in n-doped semiconductors with positive hyperfine constant is revisited. Two kinds of nuclear magnetic ordering can be induced by resident electrons in a deeply cooled nuclear spin system. At positive nuclear spin temperature below a critical value, randomly oriented nuclear spin polarons similar to that predicted by I. Merkulov [I. Merkulov, Physics of the Solid State 40, 930 (1998)] should emerge. These polarons are oriented randomly and within each polaron nuclear and electron spins are aligned antiferromagnetically. At negative nuclear spin temperature below a critical value we predict another type of magnetic ordering - dynamically induced nuclear ferromagnet. This is a long-range ferromagnetically ordered state involving both electrons and nuclei. It can form if electron spin relaxation is dominated by the hyperfine coupling, rather than by the spin-orbit interaction. Application of the theory to the n-doped GaAs suggests that the ferromagnetic order may be reached at experimentally achievable nuclear spin temperature $\Theta_N \approx 0.5$ $\mu$K and lattice temperature $T_L \approx 5$ K.

Tightly-bound trion and bandgap engineering via γ-ray irradiation in the monolayer transition metal dichalcogenide WSe2

After γ-ray irradiation treatment, a monolayer tungsten diselenide could be transitioned into an n-doped semiconductor due to the anion vacancies created by the radiation. Transmission electron microscope studies showed clear chemical modulation with atomically sharp interface. Change in the lattice vibrational modes induced by passivation of oxygen is captured by Raman spectroscopy. The frequency shifts in both in-plane and out-of-plane modes are dependent linearly on the oxidation content. We observe a negative trion, which is a neutral exciton bound with an electron, in the photoluminescence spectra. The binding energy of this trion is estimated to be ∼90 meV, making it a tightly bound exciton. The first-principles calculation suggests that an increase in the anion vacancy population is generally accompanied by a transition from a direct gap material to an indirect one. This opens up a new venue to engineer the electronic properties of transition metal dichalcogenides by using irradiation.

Efficient n‐Doping of Polymeric Semiconductors through Controlling the Dynamics of Solution‐State Polymer Aggregates

Doping of polymeric semiconductors limits the miscibility between polymers and dopants. Although significant efforts have been devoted to enhancing miscibility through chemical modification, the electrical conductivities of n-doped polymeric semiconductors are usually below 10 S cm-1 . We report a different approach to overcome the miscibility issue by modulating the solution-state aggregates of conjugated polymers. We found that the solution-state aggregates of conjugated polymers not only changed with solvent and temperature but also changed with solution aging time. Modulating the solution-state polymer aggregates can directly influence their solid-state microstructures and miscibility with dopants. As a result, both high doping efficiency and high charge-carrier mobility were simultaneously obtained. The n-doped electrical conductivity of P(PzDPP-CT2) can be tuned up to 32.1 S cm-1 . This method can also be used to improve the doping efficiency of other polymer systems (e.g. N2200) with different aggregation tendencies and behaviors.

Excited states in hydrogenated single-layer MoS2

Our calculations of the excitation spectrum of single-layer MoS2 at several hydrogen coverages, using a density-matrix based time-dependent density-functional theory (TDDFT) show that the fully hydrogenated system is metallic, while at lower coverages the spectrum consists of spin-polarized partially filled localized mid-gap states. The calculated absorption spectrum of the system reveals standard excitonic peaks corresponding to the bound valence-band hole and conduction-band electron, as well as excitonic peaks that involve the mid-gap states. Binding energies of the excitons of the hydrogenated system are found to be relatively large (few tens of meV), making their experimental detection facile and suggesting hydrogenation as a knob for tuning the optical properties of single-layer MoS2. Importantly, we find hydrogenation to suppress visible light photoluminescence, in agreement with experimental observations. In contrast, both Li and Na atoms transform the system into an n-doped non-magnetic semiconductor that does not allow excitonic states.

Experimental and theoretical study of the synthesis of N-doped TiO2 by N ion implantation of TiO2 thin films

Since major limitations of the Dye-Sensitized Solar Cells (DSSCs) efficiency are assumed to come from (i) the low resistivity of the generally used TiO2 (ρ = 1 Ω·cm) and (ii) the undesired electron-hole recombination at the semiconductor/dye-electrolyte interfaces, the development of N-doped TiO2 semiconductor (TiO2:N) has attracted considerable interest. However, the synthesis of this material still remains a challenge as it is difficult to monitor (i) the doping level and (ii) the position of the nitrogen atoms into the titanium oxide lattice. In this context, the combination of Reactive Magnetron Sputtering (RMS) and Ion implantation (II) recently allowed to finely control the nitrogen chemistry of N-doped TiO2 materials. However, the structural properties, such as the crystalline constitution and morphology of the implanted materials are of crucial interest for the intended application. Therefore, we performed a parametric study of the ion beam parameters on the physical and chemical properties of TiO2:N in the aim of charge transport application in DSSCs and the results were supplemented by a simulation tool (i.e. TRIDYN software), allowing to distinguish this work from the others. Briefly, we observed that the sputtering of the ion implanted layer prevails with low accelerating voltages while the ion implantation process and its intrinsic effects are observed for high accelerating voltage conditions. We also demonstrated that the sputtering effect issue can be quite easily avoided for low dose conditions.

Observation of carrier concentration dependent spintronic terahertz emission from n-GaN/NiFe heterostructures

The development of terahertz (THz) spintronics has created a paradigm shift in the generation of THz radiation through the combination of ultrafast magnetism and spin-based electronics. However, research in this area has primarily focused on all-metallic devices comprising a ferromagnetic thin film adjacent to a non-magnetic heavy metal. Here, we report the experimental observation of spintronic THz emission from an n-doped wide bandgap semiconductor, n-GaN. We found that the amplitude of THz emission strongly depends on the carrier concentration of the semiconductor layer, which could be attributed to the tunable Rashba state occurring at the n-GaN/ferromagnet interface. Our work offers exciting prospects for pursuing wide bandgap semiconductor-based spintronic THz devices and demonstrating their intriguing spin Hall physics at the ultrafast timescale.

Universal Limit for Air-Stable Molecular n-Doping in Organic Semiconductors.

The air sensitivity of n-doped layers is crucial for the long-term stability of organic electronic devices. Although several air-stable and highly efficient n-dopants have been developed, the reason for the varying air sensitivity between different n-doped layers, in which the n-dopant molecules are dispersed, is not fully understood. In contrast to previous studies that compared the air stability of doped films with the energy levels of neat host or dopant layers, we trace back the varying degree of air sensitivity to the energy levels of integer charge transfer states (ICTCs) formed by host anions and dopant cations. Our data indicate a universal limit for the ionization energy of ICTCs above which the n-doped semiconductors are air-stable.

Reduction Treatment of Molecular-Doped Polymer Semiconductors for High-Performance N-Channel Organic Field-Effect Transistors

Here, we study an efficient reduction treatment for improving the electron transport properties in n-type organic field-effect transistors (OFETs) based on solution-processed polymer semiconductors. If complementary-type printed electronic circuits are to be enabled, equivalently high-performance p-type and n-type organic semiconductors have to develop. Most organic semiconductors have p-type performance superior to the n-type performance. Therefore, high-performance n-type organic semiconductors and their doping process are essential. Reduced-state viologen is known to be a powerful molecular dopant via donating electrons to the conjugated polymer semiconductors. However, the reduced-state viologen readily converts to its initial ionic species under ambient conditions, which leads to insufficient n-doping performance, especially for low electron affinity organic semiconductors. N-doped polymer semiconductors using pristine viologen molecular dopants show inadequate n-channel OFET behavior. For enhancing the electron transfer doping process, solution-based reduction treatment is used to improve remarkably the performance of n-channel OFETs based on initially p-type dominant donor-acceptor-type ambipolar polymer semiconductors. This solution-processed organic active channel layer can be produced at low cost and can be applied to flexible electronic and optoelectronic devices by using various graphic art printing techniques.