Nd3+ doped fluorochlorozirconate glass:3.9 μm MIR emission properties and energy transfer

The Nd3+ doped fluorochlorozirconate (FCZ) glass was prepared by melt-quenching method. The 3.9 μm emission from Nd3+ ions is attributed to the two-photon absorption process. The strong emission transition at 3.9 μm fluorescence peak intensity, corresponding to the 4G11/2→2K13/2 transition, is directly proportional to the NaCl concentration. With the increase of the Cl- ions amount, the mid-infrared (MIR) luminescent intensity is significantly enhanced. Additionally, the Judd-Ofelt (J-O) parameter Ω2 is larger than that of the fluorozirconate (FZ) glass, which indicates the covalency of the bond between RE ions and ligand is stronger as Cl- ions substitution of F- ions in chloride FZ glass. The X-ray diffraction (XRD) patterns show that the amorphous glassy state keeps the FZ glass network structure. In brief, the advantageous spectroscopic characteristics make the Nd3+-doped FCZ glass be a promising candidate for application of 3.9 μm emission.     

N and p-type properties in organo-metal halide perovskites studied by Seebeck effects

Organo-metal halide perovskites can exhibit co-existed electrical polarizations and semiconducting properties respectively from organic and inorganic components. Here, we find that the Seebeck coefficient can be changed between positive and negative values when the concentration of chloride ions is varied between single-halide (CH₃NH₃PbI₃) and mixed-halide structures (CH₃NH₃PbI_xCl_3−x). This indicates that varying the concentration of chloride ions can tune the semiconducting properties between the n-type and p-type regimes in the organo-metal halide perovskites. Our temperature-dependent capacitance measurement shows that increasing temperature can cause a change on internal electrical polarization. As a result, we can propose that the internal polarization functions as the underlying mechanism responsible for large temperature-dependent Seebeck coefficients in organo-metal halide perovskites operating between n-type and p-type regimes.     

CoFe–Cl Layered Double Hydroxide: A New Cathode Material for High‐Performance Chloride Ion Batteries

Chloride ion batteries (CIBs) are regarded as promising energy storage systems due to their large theoretical volumetric energy density, high abundance, and low cost of chloride resources. Herein, the synthesis of CoFe layered double hydroxide in the chloride form (CoFe–Cl LDH), for use as a new cathode material for CIBs, is demonstrated for the first time. The CoFe–Cl LDH exhibits a maximum capacity of 239.3 mAh g^?1 and a high reversible capacity of ≈160 mAh g^?1 over 100 cycles. The superb Cl^? ion storage of CoFe–Cl LDH is attributed to its unique topochemical transformation property during the charge/discharge process: a reversible intercalation/deintercalation of Cl^? ions in cathode with slight expansion/contraction of basal spacing, accompanied by chemical state changes in Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺ couples. First‐principles calculations reveal that CoFe–Cl LDH is an excellent Cl^? ion conductor, with extremely low energy barriers (0.12?0.25 eV) for Cl^? diffusion. This work opens a new avenue for LDH materials as promising cathodes for anion‐type rechargeable batteries, which are regarded as formidable competitors to traditional metal ion‐shuttling batteries.     

Multilayer photosensitive structures based on porous silicon and rare-earth-element compounds: Study of spectral characteristics

The spectral characteristics of the specular reflectance, photosensitivity, and photoluminescence (PL) of multilayer structures based on porous silicon with rare-earth-element (REE) ions are investigated. It is shown that the photosensitivity of these structures in the wavelength range of 0.4–1.0 μm is higher than in structures free of REEs. The structures with Er³⁺ ions exhibit a luminescence response at room temperature in the spectral range from 1.1 to 1.7 μm. The PL spectrum of the erbium impurity is characterized by a fine line structure, which is determined by the splitting of the ⁴ I _15/2 multiplet of the Er³⁺ ion. It is shown that the structures with a porous layer on the working surface have a much lower reflectance in the entire spectral range under study (0.2–1.0 μm).     

C-V characterization of SF6 plasma treated AlGaN/GaN heterostructures

We studied influence of SF₆ plasma treatment on electrical parameters of AlGaN/GaN heterostructures by C-V, I-V and SIMS measurement. We found the C-V measurements as an effective tool that is able to help to analyze electrical manifestations of charge changes in heterostructures during the semiconductor processing. In contrary to previously published results we found out that for diminishing of the two-dimensional electron gas concentration in the channel layer positively charged ions implanted during the plasma treatment into the semiconductor and not F⁻ ions are responsible.     

Special features of the sublimational molecular-beam epitaxy of Si and its potentialities for growing Si:Er/Si structures

The concentration of charge carriers and their Hall mobility in Si:Er/Si layers grown by sublimational molecular-beam epitaxy were investigated as functions of temperature in the range of 300–77 K. No electric activity of Er-containing luminescent centers was observed. The feasibility of precise control over impurity profiles in growing the p ⁺-n-n ⁺ electroluminescent structures is demonstrated.     

Picosecond photodiffraction in semiconductor multiquantum wells and microcavities

We study the transient gratings photogenerated in the picosecond regime in three families of structures, namely : - structures of thickness in the order of one micron, including quantum wells (GaAs/GaAlAs, CdTe/ CdZnTe). A transmission modulation due to the electric field has been observed. We show that, in accordance with our calculations, this modulation is screened faster than 10 ps at a fluence of a few µJ/cm2. - A structure including GalnAs/GalnAsP MQWS in a cavity. This structure shows a top diffraction efficiency of 2.5 × 10-² at 1.55 µm for an energy of excitation in the order of 100 µJ/cm2. The diffraction efficiency exhibits several oscillations due to Fabry-Pårot effects. By introducing cavity effects in our model, we show that the diffraction efficiency is amplified by more than a factor 2 with respect to the no-cavity case. Calculations show that the diffraction efficiency may reach 6 × 10-² around 1.625 µm, for a front mirror reflectivity of 90 %. - Structures including bulk GaAs microcavities. The risetime is lower or in the order of 1 ps while the diffraction efficiency attains 1 %, with an average power of 4 mW (i.e. an energy of 2 µJ/cm²/pulse), compatible with a commutation of packets at 80 MHz.     

Formation of radiation defects in high-resistivity silicon as a result of cyclic irradiation and annealing

Transformation of radiation-induced defects in p ⁺-n-n ⁺ structures fabricated from highresistivity n-type silicon subjected to cyclic irradiation and annealing is investigated. The kinetic behavior of the increase in the concentration of the C_i-O_i defects is analyzed as a function of the detector fabrication process. During the second irradiation cycle a transformation of the defects, which were formed as a result of annealing of the original radiation defects, is observed. The appearance of “hidden” sources of deep center formation is revealed. It is established that the presence of a higher oxygen concentration, which arises in the samples as a result of the extended silicon oxidation process, results in a more active complex-formation of carbon-containing defects in comparison with samples with reduced oxygen content. Fiz. Tekh. Poluprovodn. 31, 299–304 (February 1997)     

Injection currents in silicon structures with blocked hopping conduction

It is shown that injection currents in structures with blocked hopping conduction (the so-called BIB structures) may be interpreted as Richardson thermionic currents flowing through potential barriers. The latter are governed by the electron chemical potential in the N ⁺⁺-N ⁺ (N ⁺⁺-I) regions. It is also shown that measurement of the injection potential is a convenient method for determining the degree of compensation in silicon structures with “ohmic” contacts.     

A comparison of ethyl iodide and hydrogen chloride for doping ZnSe grown by photoassisted MOVPE

We have conducted a study of the electrical and photoluminescence properties of ZnSe films grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) (250 Torr, 400°C) with ethyl iodide and hydrogen chloride as n-type dopant sources. A higher peak electron concentration and a lower minimum resistivity were observed using hydrogen chloride (5.4 × 10¹⁸ cm⁻³, and .0070 ohm-cm, respectively), as opposed to ethyl iodide (1.55 × 10¹⁷ cm ⁻³, and 0.067 ohm-cm, respectively). We show that the higher electron concentrations observed in the chlorine doped layers are due to a higher incorporation of chlorine atoms than that of iodine atoms, and that this may be a result of the different tetrahedral misfit factors for these atoms. Our photoluminescence and 77K Hall effect data support this conclusion. Growth rate depression was observed to be more severe for iodine doped layers than for chlorine doped layers. Thus, it appears that hydrogen chloride is a superior dopant source for low-temperature photoassisted MOVPE ZnSe growth of n-type layers for blue-green laser diodes in the pressure-temperature regime investigated.     

Effect of neutron irradiation on the structure of silicon p-n junctions of voltage limiters

Changes in capacitance-voltage characteristics of p-n junctions with a linear or close-to-linear uncompensated charge distribution under neutron irradiation are analyzed. It is confirmed that an intrinsic conductivity region is formed near the p-n junction due to such exposure. Empirical formulas are derived which describe the dependence of the sizes of this region and the effective concentration gradient of uncompensated charge on the neutron fluence in a wide range of initial (before neutron irradiation) concentration gradients (from 3 × 10¹⁸ to 2 × 10²⁰ cm^?4) and initial silicon resistivities (from 0.3 to 2 Ω cm).     

Effect of irradiation with fast neutrons on electrical characteristics of devices based on CVD 4<Emphasis Type="Italic">H</Emphasis>-SiC epitaxial layers

The effect of irradiation with 1-MeV neutrons on electrical properties of Al-based Schottky barriers and p⁺-n-n⁺ diodes doped by ion-implantation with Al was studied; the devices were formed on the basis of high-resistivity, pure 4H-SiC epitaxial layers possessing n-type conductivity and grown by vapor-transport epitaxy. The use of such structures made it possible to study the radiation defects in the epitaxial layer at temperatures as high as 700 K. Rectifying properties of the diode structures were no longer observed after irradiation of the samples with neutrons with a dose of 6×10¹⁴ cm^?2; this effect is caused by high (up to 50 GΩ) resistance of the layer damaged by neutron radiation. However, the diode characteristics of irradiated p⁺-n-n⁺ structures were partially recovered after an annealing at 650 K.     

Plasmon–phonon coupling in the infrared reflectance spectra of Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> films

The results of studies of optical reflection in the far- and mid-infrared spectral regions are reported. The reflectance of five Bi₂Se₃ topological insulator films grown by molecular-beam epitaxy on Si(111) substrates is measured. The characteristic parameters of phonons and plasmons are determined by means of dispersion analysis for multilayer structures. It is found that the plasma frequency in a layer close to the Si–film interface is noticeably higher than that in the film bulk. Calculations of the loss function show that plasmon–phonon coupling plays an important role in Bi₂Se₃ films. The attenuated total internal reflection method is used to determine the frequency of the surface plasmon–phonon mode.     

Effect of low-temperature annealing on characteristics of SiC detectors with radiation-induced defects

p ⁺-n-n ⁺ detector structures based on CVD films with an uncompensated donor concentration of 2 × 10¹⁴ cm^?3 have been studied. The p ⁺-region was created by implantation of Al ions. The detectors were preliminarily irradiated with 8-MeV protons at a fluence of 3 × 10¹⁴ cm^?2 and then annealed at 600°C for 1 h. In measurements performed in the temperature range 20–150°C, the forward-and reverse-bias modes were compared. It is shown that the annealing leads to a higher collection efficiency of carriers generated by nuclear radiation and to a decrease in the amount of charge accumulated by traps in the course of testing. Despite the positive effect of the annealing, a considerable amount of radiation defects remain, which is manifested, in particular, in the kinetics of the forward current.     

The effect of dislocations formed during growth on the structure and photoluminescence of i-n −-n-n +-GaAs epilayers and on the related microwave transistors parameters

The structure of two types of GaAs i-n ^?-n-n ⁺ epilayers on GaAs〈100〉 semi-insulating substrates was studied by electron microscopy. The low-temperature photoluminescence spectra were measured and their special features were analyzed. It is shown that the formation of dislocations during growth in such structures significantly affects the photoluminescence spectra and impairs the parameters of microwave field-effect transistors based on these structures.     

Potential and limitations of Schottky-barrier barritt devices

Computer simulation of various Schottky-barrier structures is carried out to investigate the large-signal properties of these devices. Comparison between Schottky-barrier devices and their p-n junction counterparts are also made to evaluate the potential and limitations of these devices and to explain the difference in performance between them. It is shown that among various Schottky-barrier structures, the M-n-i-p⁺ structure is the most powerful one and the M-n-p-p⁺ device is the most efficient one. Furthermore, Schottky-barrier devices with low barrier heights for minority carriers (less than 0.2 eV) are capable of producing power levels close to the generated power of p-n junction devices. Investigation of the temperature dependence of the large-signal performance of these devices shows that Schottky barriers are more sensitive and exhibit their optimum performance close to room temperature value. At low temperature, the output power is limited by the low minority carrier injection, whereas at high temperature the limitation is due to the velocity-modulation losses in the injection and low-field regions of the device.     

Direct Patterning of Self‐Assembled Monolayers by Stamp Printing Method and Applications in High Performance Organic Field‐Effect Transistors and Complementary Inverters

Self‐assembled monolayer (SAM) is usually applied to tune the interface between dielectric and active layer of organic field‐effect transistors (OFETs) and other organic electronics, a time‐saving, direct patterning approach of depositing well‐ordered SAMs is highly desired. Here, a new direct patterning method of SAMs by stamp printing or roller printing with special designed stamps is introduced. The chemical structures of the paraffin hydrocarbon molecules and the tail groups of SAMs have allowed to use their attractive van der Waals force for the direct patterning of SAMs. Different SAMs including alkyl and fluoroalkyl silanes or phosphonic acids are used to stamp onto different dielectric surfaces and are characterized by water contact angle, atomic force microscopy, X‐ray diffraction, and attenuated total reflectance Fourier transform infrared. The p‐type dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) and n‐type F₁₆CuPc OFETs show competitive mobility as high as 3 and 0.018 cm² V^?1 s^?1, respectively. This stamp printing method also allows to deposit different SAMs on certain regions of same substrate, and the complementary inverter consists of both p‐type and n‐type transistors whose threshold voltages are tuned by stamp printing SAMs and shows a gain higher than 100. The proposed stamp or roller printing method can significantly reduce the deposition time and compatible with the roll‐to‐roll fabrication.     

Influence of the electron-hole equilibrium shift on transition-metal diffusion in GaAs

Diffusion of impurities of transition metals Fe, Cu, and Cr in heavily doped p ⁺-, n ⁺-, and intrinsic (at diffusion temperature) GaAs is studied. A technique in which impurity diffuses into GaAs-based structures with heavily doped layers (p ⁺-n or n ⁺-n) was used. It is shown that the impurity diffusivity values in p ⁺-GaAs and n ⁺-GaAs are significantly higher and lower, respectively, than for i-GaAs. The results obtained are discussed taking into account the effect of the electron-hole equilibrium shift in semiconductors on the diffusion of impurities migrating according to the dissociative mechanism. The interstitial-component concentration for Fe, Cu, and Cr impurities in GaAs was determined at the diffusion temperature.     

Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

Charge-carrier exclusion and accumulation intensified by ohmic contacts

The effect of the high generation-recombination power of an ohmic contact (S contact) on exclusion-accumulation processes in structures with an antiblocking contact (asymmetric structures of the type p ⁺-p-S) was studied theoretically and experimentally. It is shown that, in contrast to the ordinarily studied symmetric structure p ⁺-p-p ⁺, the asymmetric structures, which is being studied, forms a region of accumulation or exclusion, depending on the direction of the current. The nonequilibrium carrier density in the accumulation layer is much higher while the exclusion region is longer than in the symmetric structure. A density n 100 times higher than the equilibrium value n ₀ was obtained experimentally for Ge at 300 K. The length of the exclusion region reached 96% of the sample length. Applications of structures with antiblocking and ohmic contacts based on narrow-gap materials are proposed. Fiz. Tekh. Poluprovodn. 32, 634–637 (May 1998)