Concentration Of Free Charge Carriers Research Articles

Determination of the Free Charge Carrier Concentration in Boron-Doped Silicon Nanowires Using Attenuated Total Reflection Infrared Spectroscopy

Attenuated total reflection infrared spectroscopy is used to determine the free charge carrier concentration in arrays of silicon nanowires with characteristic transverse sizes of 50–100 nm and a length of the order of 10 μm formed on lightly doped crystalline p-type silicon by metal-assisted chemical etching and subjected to the additional thermal-diffusion doping of boron at temperatures of 850–1000°C. It is found that the free hole concentration in arrays varies from 5 × 1018 to 3 × 1019 cm–3 depending on the annealing temperature and is maximal at temperatures of 900–950°C. These results can be used to extend the range of potential application of silicon nanowires in photonics, sensorics, and thermoelectric power converters.

Determination of Electrophysical Parameters of a Semiconductor from Measurements of the Microwave Spectrum of Coaxial Probe Impedance

We propose a method for determining electrophysical characteristics (free charge carrier concentration, mobility, and conductivity) of semiconductors from the results of measurements of the microwave spectrum of the impedance of a coaxial probe as a function of applied constant voltage U. The sought parameters have been determined by solving the corresponding inverse problem using the theory of a near-field antenna that was developed earlier. We have developed a computer program that seeks the solution by minimization of the multiparametric residual function in accordance with the Nelder–Mead algorithm. The precision of the method has been analyzed from the results of simulation in which the impedance was calculated preliminarily considering resultant concentration profile n(x, U) of the depleted layer in the vicinity of the metal–semiconductor contact. The possibility of diagnostics with a micrometer lateral resolution has been demonstrated.

Effect of Conductivity Type and Doping Level of Silicon Crystals on the Size of Formed Pore Channels during Anodic Etching in Hydrofluoric Acid Solutions

In this paper, we discuss causes of the multidirectional effect of changes in the concentrations of free charge carriers in silicon crystals of p- and n-type conductivity on the transverse dimensions of pores formed as a result of anodic etching in hydrofluoric acid solutions, as well as the effect of anodic current density on pore size. The observed dependences are explained based on the concepts of electrochemical pore formation in semiconductor crystals as self-organizing cooperative processes accompanied by the injection of electrons from the chemical reaction region at the pore advancement front. Differences in the size of pores forming at the same current density in crystals differing in type and concentration of free charge carriers are associated with the effective temperature of the front of the cooperative chemical reaction at the bottom of germinating pores. This temperature, in turn, correlates with the power density of thermal energy released in the near-surface region of the etching crystal, either due to recombination processes for a p-type semiconductor or direct or indirect energy transfer from hot electrons to lattice vibrations in the case of a n-type semiconductor. The characteristic relaxation times of injected nonequilibrium electrons were calculated depending on the concentrations of the majority charge carriers in silicon crystals of both types of conductivity and the corresponding thicknesses of the regions of relaxation energy release. The revealed patterns of concentration changes in the power density of heat release in the near-frontal region of etching silicon crystals of p- and n-type conductivity are in good agreement with observed changes in the size of germinating pores.

Thermal annealing effect on the structural and optical characteristics of silicon phthalocyanine dichloride thin films

The crystal structure of silicon phthalocyanine dichloride (SiPcCl2) was studied using X-ray diffraction (XRD). The SiPcCl2 powder was polycrystalline and transformed to an amorphous form for pristine and annealed thin films. The prepared films were annealed at 363 K, 403 K, 543 K and 493 K for 2 h in a drying oven. The optical characteristics of these films were studied under normal light incidence in wavelength range from 190 to 2500 nm using spectrophotometry technique. The electronic transition type is an indirect allowed transition with optical and onset energy gaps of 1.92 eV and 1.25 eV, respectively. As the temperature rised, the defects gradually disappeared and the localized density of states tended to decrease; thus, the optical energy gap increased. The annealing effect on optical parameters, such as the real (ε1) and imaginary (ε2) parts of the dielectric constant, the volume energy loss function (VELF) and the surface energy loss function (SELF), was studied. The ratio between the free charge carrier concentration and the effective mass (N/m*), the lattice dielectric constant (εL), the infinite frequency dielectric constant (ε∞), the oscillator energy (Eo) and the dispersion energy (Ed) were calculated before and after thermal annealing.

A Study on Effect of Sol Aging Time on Optical Properties of ZnO Thin Films: Spectroscopic Ellipsometry Method

Background: Due to wide band gap and large excitonic binding energy, being inexpensive, abundance in nature and easy synthesis ZnO is a promising candidate in many applications such as solar cells. Experimental: In the current work a series of ZnO thin films were deposited on glass substrates using sol-gel method to investigate the change in optical behavior of the film with sol aging time (asprepared, 8, 16, 24 and 32 hours) and the annealing temperature (300ᵒC and 500ᵒC). The optical properties of thin films were explored using spectroscopic ellipsometry method including the real and imaginary part of refractive index, real and imaginary part of dielectric function and band gap energy of the layers in the 300-900 nanometer wavelength range. Results: It can be deduced from the results that sol aging time and annealing temperature, affect the optical properties of the samples. Using single oscillator energy model of Wemple and Di Domenico parameters such as free charge carrier concentration ratio to effective mass, and plasma frequency, were calculated. Conclusion: The films prepared using 24 h aged solution, had the highest transmittance and the largest band gap energy.

Surface Depletion Layers in Plasmonic Metal Oxide Nanocrystals.

Strong infrared (IR) light-matter interaction and spectral tunability combine to make plasmonic metal oxide nanocrystals (NCs) a compelling choice for IR applications. In particular, visible transparency paired with strong, dynamically tunable IR absorption has motivated their implementation in electrochromic smart windows, but these NCs hold promise for a far broader range of plasmonically driven processes such as surface-enhanced infrared sensing, photothermal therapy, and enhanced photocatalysis. These unique properties result from localized surface plasmon resonance (LSPR) sustained by a relatively low free charge carrier concentration, which in turn requires consideration of distinct materials physics relative to traditional plasmonic materials (i.e., metals). Particularly important is the formation of insulating shells devoid of charge carriers (depletion layers) near the NC surface. Surface states as well as applied surface potentials can give rise to a potential difference between the NC surface and its core that depletes free charge carriers from the surface, forming an insulating shell that reduces the conductivity in NC films, lowers the dielectric sensitivity of the LSPR, and diminishes the incident electric field enhancement. In this Account, we report recent investigations of depletion layers in plasmonic metal oxide NCs that have advanced understanding of the semiconductor physics underlying the optoelectronic properties of these NCs and the electrochemical modulation of their LSPR, establishing a conceptual framework with which to broaden their applicability and optimize their performance. As a result of surface depletion, larger, highly doped NCs have improved dielectric sensitivity compared with their smaller, lightly doped counterparts. Concentrating dopants near the NC surface compresses the depletion layer, resulting in improved conductivity of NC films. Moreover, atomic layer deposition of alumina to infill NC films enhances the film conductivity by more than 2 orders of magnitude, ascribed to the elimination of depletion effects by reactive removal of surface water species. At the conclusion, we reflect on how our newfound understanding of surface depletion in plasmonic metal oxide NCs is quickly leading to rational material design. This insight is already resulting in significant performance improvements, and the same principles can be applied to new, exciting opportunities in hot carrier extraction and resonant IR energy transduction.

Infrared Diagnostics of Free Charge Carriers in Silicon Nanowires

Free charge carrier concentration in arrays of silicon nanowires (SiNWs) with cross-sectional size of the order of 100[Formula: see text]nm was quantitatively studied by means of the infrared spectroscopy in an attenuated total reflection mode. SiNWs were formed on lightly-doped [Formula: see text]-type crystalline silicon substrates by metal-assisted chemical etching followed by additional doping through thermoactivated diffusion of boron at 900–1000∘C. The latter process was found to increase the concentration of free holes in SiNWs up to [Formula: see text][Formula: see text]cm[Formula: see text]. Potential applications of highly doped SiNWs in thermoelectric energy converters and infrared plasmonic devices are discussed.

Влияние типа проводимости и уровня легирования кристаллов кремния на размеры каналов пор, формирующихся в них при анодном травлении в растворах плавиковой кислоты

AbstractIn this paper, we discuss causes of the multidirectional effect of changes in the concentrations of free charge carriers in silicon crystals of p - and n -type conductivity on the transverse dimensions of pores formed as a result of anodic etching in hydrofluoric acid solutions, as well as the effect of anodic current density on pore size. The observed dependences are explained based on the concepts of electrochemical pore formation in semiconductor crystals as self-organizing cooperative processes accompanied by the injection of electrons from the chemical reaction region at the pore advancement front. Differences in the size of pores forming at the same current density in crystals differing in type and concentration of free charge carriers are associated with the effective temperature of the front of the cooperative chemical reaction at the bottom of germinating pores. This temperature, in turn, correlates with the power density of thermal energy released in the near-surface region of the etching crystal, either due to recombination processes for a p -type semiconductor or direct or indirect energy transfer from hot electrons to lattice vibrations in the case of a n -type semiconductor. The characteristic relaxation times of injected nonequilibrium electrons were calculated depending on the concentrations of the majority charge carriers in silicon crystals of both types of conductivity and the corresponding thicknesses of the regions of relaxation energy release. The revealed patterns of concentration changes in the power density of heat release in the near-frontal region of etching silicon crystals of p - and n -type conductivity are in good agreement with observed changes in the size of germinating pores.

Неразрушающий контроль поверхности, слоев и концентрации носителей заряда в подложках и структурах SiC

Abstract Silicon carbide substrates and epitaxial structures are investigated by nondestructive contactless methods. Parameters of the disrupted surface layer and roughnesses are determined using ellipsometry and atomic force microscopy. The free charge carrier concentration is determined by IR spectroscopy. The thicknesses in the multilayer epitaxial structure on SiC are determined using IR spectroscopy and scanning electron microscopy.

Определение электрофизических параметров полупроводника по измерениям микроволнового спектра импеданса коаксиального зонда

We propose a method for determining semiconductors electrophysical characteristics (concentration and mobility of free charge carriers, conductivity) using measurements of the microwave impedance spectrum of a coaxial probe as a function of the applied constant voltage U. The parameters under study are found by solving the corresponding inverse problem using the developed theory of the near-field antenna. A computer program was created that searches for a solution by minimizing the multiparameter discrepancy function using the Nelder–Mead algorithm. The accuracy of the method is analyzed from simulation results in which the impedance is calculated via the obtained charge concentration profile n(x, U) of the depleted layer in the vicinity of the metal-semiconductor contact. The possibility of diagnostics with micron lateral resolution is demonstrated.

Определение концентрации свободных носителей заряда в легированных бором кремниевых нанонитях при помощи инфракрасной спектроскопии в режиме нарушенного полного внутреннего отражения

Attenuated total reflection infrared spectroscopy was used to determine the free charge carrier concentration in the arrays of silicon nanowires of characteristic transverse dimension of 50–100 nm and the length of the order of 10 μm which were formed on low-doped crystalline p-type silicon via metal-stimulated chemical etching and subjected to additional thermodiffusion boron doping at the temperatures 850–1000 оС. It was found out that the free hole concentration varies from 5•1018 to 3•1019 cm-3 depending on the annealing temperature and reaches it’s maximum at 900–950 оС. The results can be used to expand the scope of silicon nanowires application in photonics, sensorics and thermoelectric power converters.

Giant enhancement of free charge carrier concentration in boron-doped amorphous hydrogenated silicon under femtosecond laser crystallization

The modification of boron-doped amorphous hydrogenated silicon films [a-Si:H(B)] with femtosecond laser radiation is studied in this work. It is demonstrated that femtosecond laser crystallization of the a-Si:H(B) film area leads to extremely high values of the free charge carrier (hole) concentration, which is typical for degenerated semiconductors. The free charge carrier concentration is locally determined by measuring the Raman spectra in the modified areas. The shape of Raman spectra is typical for Fano resonance. It is found that the charge carrier concentration in the modified areas may exceed 1020 cm−3 depending on the femtosecond irradiation conditions. The areas with such a high concentration of free charge carriers are also characterized by high volume fraction of crystalline phase (more than 90%). Such a sharp increase in the free charge carrier concentration in the modified areas may be explained by an increase in concentration of electrically active boron atoms. The activation energy of the temperature dependence of the conductivity for laser beam treated areas is in full agreement with the data obtained from the analysis of the Raman scattering spectra.

Influence of metal/semiconductor interface on attainable piezoelectric and energy harvesting properties of ZnO

The piezoelectric coefficient is a measure to quantify the potential use of a material in energy harvesting and sensor applications. High concentration of free charge carriers in piezoelectric materials can significantly impede the use of generated piezoelectric charge. In this study, undoped semiconducting ZnO single crystals with both Ohmic and Schottky contacts were prepared to quantify the effective piezoelectric response at temperatures from 20 °C to −140 °C and frequencies of mechanical loading from 0.5 Hz to 160 Hz. It was demonstrated that the formation of an electrostatic potential barrier at the metal-semiconductor interface increases the overall resistance, which provides access to unbiased piezoelectric coefficients of ZnO single crystals even at room temperature. These findings were verified using semiconducting ZnO for energy harvesting at room temperature and relatively low loading frequency.

Structural and opto-electrical characterization of sodium -2,3-dicyano-5,6-dichloro-1,4-benzo-quinone (Na-DDQ) as complex thin films

In this study, sodium -2,3-dicyano-5,6-dichloro-1,4-benzo-quinone (Na-DDQ) as-deposited thin films were synthesized by the conventional thermal evaporation facility. The crystal structure of (Na-DDQ) compound in the form of powder and thin film were inspected using X-ray diffraction (XRD) and Fourier transformation infrared (FTIR) techniques. Subsequently, the lattice parameters and Miller's indices, hkl, were calculated for all individual peaks in the XRD pattern of the fine powder form and suggests a polycrystalline with Orthorhombic structure. The optical properties of the as-deposited thin films were inspected by measuring the reflectance and transmittance in the wavelength range between 200–2500 nm using spectrophotometric. The estimated spectral of refractive index, n, and absorption index, k, were used to extract the spectra of dielectric constant, surface and volume energy loss functions, optical conductivity, relaxation time along with optical electronegativity.Furthermore, in the normal dispersion region, the optical parameters such as oscillator energy, Eo, dispersion energy, Ed, lattice dielectric constant, εL, infinity dielectric constant, ε∞, and the ratio of the free charge carrier concentration of the effective mass, N/m* were estimated. Moreover, the Drude theory applied to extract Opto-electrical parameters, such as the concentration of optical carrier, optical mobility, and optical resistivity. Finally, the electronic transitions of as-deposited thin film and the extinction molar coefficient, εmolar, oscillator strength and the electric dipole strength were calculated for the films.

Systems of Manganites with Enhanced Electromagnetic Parameters

The effects of paired substitution of 3d10 cations ( $$\rm{Zn{_{0.5}^{2+}}Ge{_{0.5}^{4+}}}$$ ) or 2p6 and 3p6 cations ( $$\rm{Mg{_{0.5}^{2+}}Ti{_{0.5}^{4+}}}$$ ) for manganese in polycrystalline manganites of specifically designed systems $$\text{L}{\text{a}_{0.8 - x}}\text{S}{\text{r}_{0.2 + x}}\text{Mn}_{0.8 - 2x -2\gamma}^{3 +}\text{Mn}_{0.2 + x + 2\gamma}^{4 +} \times {\left( {\text{Me}_{0.5}^{2 +}\text{Me}_{0.5}^{4 +}} \right)_x}{\text{O}_{3 + \gamma}}$$ on their electromagnetic parameters are studied and compared. Temperature dependences of the resistance, magnetoresistance and magnetostriction constant are measured. In the proposed systems, the linear rise of strontium concentration simultaneously with increasing number of substituents allows high characteristics of manganites to be maintained owing to the increase in the concentration of free charge carriers, through which ferromagnetic double exchange interaction is carried out. The data obtained are also compared with the properties of Ga3+(3d10)-substituted manganites as peculiar standards. All sintered (Zn,Ge)-containing manganites in the temperature range from 100 to 293 K have metallic type of conductivity, while (Mg,Ti)-substituted samples exhibit semiconducting features, and Ga-containing compositions reveal a “metal-semiconductor” transition point (Tms). The annealing under conditions ensuring stoichiometric oxygen content leads to the shift of this transition toward lower temperatures in manganites with 3d10 substituents and to the increase in Tms in compositions with substituting p6 cations. In the investigated systems, the absolute values of negative magnetoresistance up to ~90–200% at 120–150 K in the field of 9.2 kOe are obtained, and the linear magnetostriction constant reaches record values of about 10–3 in the field of 4.6 kOe. Manganite La0.65Sr0.35Mn0.85Ga0.15O3 with a weak temperature dependence of magnetoresistance of ~20% at room temperatures is of particular service for magnetic field sensors. Possible approaches to the interpretation of established regularities demonstrating the role of electronic configurations of substituents for manganese in the formation of the properties of manganites and interesting for the development of new materials for electronics are discussed.

Quasi-Chemistry of Intrinsic Point Defects in Cadmium Telluride Thin Films

The defect formation in cadmium telluride thin films when growing from the vapor phase by a hot-wall epitaxy method has been described with the help of quasi-chemical reactions. The analytical expressions of the dependences of concentration of free charge carriers and dominant intrinsic atomic defects on the technological factors (substrate temperature тS, evaporation temperature тE and partial vapor pressure of cadmium ) have been obtained. It has been shown that the concentration of free charge carriers in CdTe films is determined by vacancies of cadmium and tellurium.

Influence of surface topography and annealing temperature on the surface and volume of dissipation electrical energy and Spitzer–Fan model in Al doped ZnO films

The aim of this work is to investigate the optical constants of aluminum doped zinc oxide films annealed at different temperatures. With increasing temperature, due to decreasing unfilled inter-granular volume per unit thickness, the optical transmittance spectra of films were increased. The films have a normal dispersion in the spectral range 400 < λ < 500 nm and the anomalous dispersion in IR range. The lattice dielectric constants eL, the free charge carriers concentration, the plasma frequency, Spitzer–Fan model and the waste of electrical energy as heat of films can be analyzed using the refractive index n and the extinction coefficient k spectra. With increasing annealing temperature, the lattice dielectric constants eL of films decrease however the free charge carriers concentration of films increase. The free carrier electric susceptibility of films annealed at 600 °C has maximum value. The energy loss by the free charge carriers when traversing the bulk and surface of films annealed at 600 °C has a minimum value in the near fundamental absorption edge and it with increasing energy increases.

Structural, dispersion and optical functions studies of UV-irradiated erythrosine B thin films prepared by spin coating technique

XRD Diffraction measurements show that the powder of erythrosine B has poly-structure but very homogeneous thin films of erythrosine B have been successfully performed on a quartz substrate using the spin coating techniques and the structure of deposited films has been changed into amorphous form. The effect of UV radiation onto the erythrosine B thin films has been studied. XRD diffraction spectra indicate no influence of UV radiation upon the amorphous structure of erythrosine B thin films. The spectral behavior and optical properties of thin films were determined using spectrophotometric measurements of transmittance and reflectance in the wavelength range 200–2500 nm. Optical measurements of pristine and UV-irradiated erythrosine B films showed normal dispersion of the refractive index n at λ > 850 nm and anomalous dispersion at λ < 850 nm. The dispersion curve showed different response to UV irradiation depending on the wavelength of incident light. The dispersion curve showed different response to UV irradiation depending on the wavelength of incident light. Some of dispersion parameters such as the high-frequency dielectric constant (e∞), the lattice dielectric constant (eL), the dispersion energy (Ed), ratio of the free charge carrier concentration to effective mass (N/m*) and the oscillator energy (Eo) were calculated. The optical functions such as the real (e1), imaginary (e2) parts of the dielectric constant, the real (σ1), imaginary (σ2) parts of electrical conductivity, and the volume and the surface energy loss (VEL and SEL) were estimated and their response to UV irradiation was discussed.

Probing of Free Charge Carriers in Nanostructured Silicon Layers by Attenuated Total Reflectance Technique

Infrared spectroscopy in attenuated total reflection (ATR) mode is used to evaluate the concentration of free charge carriers (electrons) in n‐type macroporous silicon (Si) layers formed by metal‐assisted chemical etching of crystalline silicon (c‐Si) followed by additional doping with phosphorus. The ATR spectra are fitted by considering an effective medium approximation and Drude model, which is modified to describe an additional scattering of the charge carriers on the surface of Si nanocrystals. The electron concentration is of the order of 1019 cm−3 and it is slightly dependent on the layer thickness, while the surface scattering of charge carriers increases with layer thickness. The obtained results are discussed in view of possible applications of the ATR method for an express diagnostics of doping efficiency of Si nano‐ and microstructures for photonic and thermoelectrical applications.

Electronic functionality of Gd-bisphthalocyanine: Charge carrier concentration, charge mobility, and influence of local magnetic field

Gadolinium bisphthalocyanine (GdPc2) has been placed among the highest ranked molecular materials considered namely for modern optoelectronic applications including organic solar cells. To improve understanding of the correlation between GdPc2 magnetic properties and its electronic functionality, we experimentally and theoretically studied charge carrier concentration, charge mobility, and influence of local magnetic field on charge carrier transport. For better clearance, all the main studied properties of GdPc2 bisphthalocyanine were compared with Zn phthalocyanine (ZnPc) as a reference material. Conductivity and charge carrier mobility were measured in materials incorporated in FET active channels. UV Vis spectroscopy, Electron Paramagnetic Resonance Spectroscopy, and IR spectroscopy were also applied. The narrow band gap together with small ionization potential of GdPc2 lead to high free charge carrier concentration. Among parameters affecting charge carrier mobility, molecular arrangement and intermolecular and intramolecular charge carrier pathways were highlighted. The possibility that the interaction of the mobile charge carriers with the local magnetic field of GdPc2 molecules reduces charge carrier mobility is also discussed.