卷 51, 编号 2 (2017)
- 年: 2017
- 文章: 25
- URL: https://journals.rcsi.science/1063-7826/issue/view/12445
Electronic Properties of Semiconductors
Features of the band structure and conduction mechanisms of n-HfNiSn heavily doped with Y
摘要
The crystalline and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with Y acceptor impurity are studied in the ranges: T = 80–400 K, NAY ≈ 1.9 × 1020–5.7 × 1021 cm–3 (x = 0.01–0.30), and H ≤ 10 kG. The nature of the mechanism of structural defect generation is determined, which leads to a change in the band gap and the degree of semiconductor compensation, the essence of which is the simultaneous reduction and elimination of structural donor-type defects as a result of the displacement of ~1% of Ni atoms from the Hf (4a) site, and the generation of structural acceptor-type defects by substituting Hf atoms with Y atoms at the 4a site. The results of calculations of the electronic structure of Hf1–xYxNiSn are in agreement with the experimental data. The discussion is performed within the Shklovskii–Efros model of a heavily doped and compensated semiconductor.
Electrical properties and transport mechanisms in phase change memory thin films of quasi-binary-line GeTe–Sb2Te3 chalcogenide semiconductors
摘要
The temperature dependences of the resistivity and current–voltage (I–V) characteristics of phase change memory thin films based on quasi-binary-line GeTe–Sb2Te3 chalcogenide semiconductors Ge2Sb2Te5, GeSb2Te5, and GeSb4Te7 are investigated. The effect of composition variation along the quasibinary line on the electrical properties and transport mechanisms of the thin films is studied. The existence of three ranges with different I–V characteristics is established. The position and concentration of energy levels controlling carrier transport are estimated. The results obtained show that the electrical properties of the thin films can significantly change during a shift along the quasi-binary line GeTe–Sb2Te3, which is important for targeted optimization of the phase change memory technology.
On the thermopower and thermomagnetic properties of ErxSn1–xSe solid solutions
摘要
The ErxSn1–xSe system is characterized by a significant deviation of the temperature dependence of the differential thermopower from linearity at temperatures below room temperature and a change in the sign of the thermomagnetic coefficient. The deviation of the thermopower of ErxSn1–xSe samples in the nonequilibrium state from linearity is found to be caused mainly by the entrainment of charge carriers by phonons αph. The statistical forces of electronic entrainment, Aph(ε), are estimated.
Field diffusion in disordered organic materials under conditions of occupied deep states
摘要
A simple analytical model of the field-diffusion coefficient is developed for moderate carrier concentrations. Hopping transport is described by the multiple-trapping model based on the transport-level concept. A continuity equation with a diffusion coefficient depending on carrier concentration is obtained, the time dependence of the field-diffusion coefficient under non-steady-state conditions is found. The time intervals in which deep state population affects the mobility and diffusion coefficient under conditions of time-of-flight experiments are estimated. It is shown that the field-diffusion coefficient increases in a long time interval while the mobility is unchanged, which is reminiscent of a similar case of nonequilibrium initial carrier generation at the low-concentration limit.
Magnetic-field-dependent microwave absorption in HgSe in weak magnetic fields
摘要
The low-temperature magnetoresistive effect in the semiconductor HgSe:Fe in weak magnetic fields at microwave frequencies is examined. The negative and positive components of magnetoabsorption based on the magnetoresistive effect in the degenerate conduction band are analyzed. The special features of experiments carried out in the investigated frequency range are noted. The momentum and electron-energy relaxation times are determined from the experimental field and temperature dependences.
Spectroscopy, Interaction with Radiation
Raman scattering in InP doped by Be+-ion implantation
摘要
InP (100) crystals implanted with Be+ ions with an energy of 100 keV and doses of 1013–1015 cm–2 are studied by Raman spectroscopy before and after thermal annealing at temperatures of 300–850°C. It is found that, as the implanted ion dose is increased, the surface region of InP is partially amorphized; in this case, spectral lines related to longitudinal lattice vibrations exhibit a shift to lower frequencies and inhomogeneous broadening, which is indicative of the formation of a nanocrystalline phase. Thermal annealing results in recovery of the crystal structure of InP. At annealing temperatures of >700°C, scattering at phonon–plasmon coupled modes is detected in the Raman spectra. This is attributed to electrical activation of the impurity. From the frequency of the phonon–plasmon mode, the concentration of heavy holes is estimated in the context of the model of a two-oscillator dielectric function.
Surfaces, Interfaces, and Thin Films
Influence of the doping type and level on the morphology of porous Si formed by galvanic etching
摘要
The formation of porous silicon (por-Si) layers by the galvanic etching of single-crystal Si samples (doped with boron or phosphorus) in an HF/C2H5OH/H2O2 solution is investigated. The por-Si layers are analyzed by the capillary condensation of nitrogen and scanning electron microscopy (SEM). The dependences of the morphological characteristics of por-Si (pore diameter, specific surface area, pore volume, and thickness of the pore walls), which determine the por-Si combustion kinetics, on the dopant type and initial wafer resistivity are established.
Study of silicon doped with zinc ions and annealed in oxygen
摘要
The results of studies of the surface layer of silicon and the formation of precipitates in Czochralski n-Si (100) samples implanted with 64Zn+ ions with an energy of 50 keV and a dose of 5 × 1016 cm–2 at room temperature and then oxidized at temperatures from 400 to 900°C are reported. The surface is visualized using an electron microscope, while visualization of the surface layer is conducted via profiling in depth by elemental mapping using Auger electron spectroscopy. The distribution of impurity ions in silicon is analyzed using a time-of-flight secondary-ion mass spectrometer. Using X-ray photoelectron spectroscopy, the chemical state of atoms of the silicon matrix and zinc and oxygen impurity atoms is studied, and the phase composition of the implanted and annealed samples is refined. After the implantation of zinc, two maxima of the zinc concentration, one at the wafer surface and the other at a depth of 70 nm, are observed. In this case, nanoparticles of the Zn metal phase and ZnO phase, about 10 nm in dimensions, are formed at the surface and in the surface layer. After annealing in oxygen, the ZnO · Zn2SiO4 and Zn · ZnO phases are detected near the surface and at a depth of 50 nm, respectively.
Study of the deposition features of the organic dye Rhodamine B on the porous surface of silicon with different pore sizes
摘要
The deposition features of the organic dye Rhodamine B on the porous surface of silicon with average pore sizes of 50–100 and 100–250 nm are studied. Features of the composition and optical properties of the obtained systems are studied using infrared and photoluminescence spectroscopy. It is found that Rhodamine-B adsorption on the surface of por-Si with various porosities is preferentially physical. The optimal technological parameters of its deposition are determined.
Semiconductor Structures, Low-Dimensional Systems, and Quantum Phenomena
Electroreflectance spectra from multiple InGaN/GaN quantum wells in the nonuniform electric field of a p–n junction
摘要
A line at E = 2.77 eV (with a width of Γ = 88 meV) related to interband transitions in the region of multiple quantum wells in the active region is detected in the electroreflectance spectra of the GaN/InGaN/AlGaN heterostructure. As the modulation bias is reduced from 2.9 to 0.4 V, the above line is split into two lines with energies of E1 = 2.55 eV and E2 = 2.75 eV and widths of Γ1 = 66 meV and Γ2 = 74 meV, respectively. The smaller widths of separate lines indicate that these lines are caused by interband transitions in particular quantum wells within the active region. The difference between the interband transition energies E1 and E2 in identical quantum wells in the active region is related to the fact that the quantum wells are in an inhomogeneous electric field of the p–n junction. The magnitudes of the electric-field strengths in particular quantum wells in the active region of the heterostructure are estimated to be 1.6 and 2.2 MV/cm.
New mechanism of semiconductor polarization at the interface with an organic insulator
摘要
A semiconductor—organic-insulator system with spatially distributed charge is created with a uniquely low density of fast surface states (Nss) at the interface. A system with Nss ≈ 5 × 1010 cm–2 is obtained for the example of n-Ge and the physical characteristics of the interface are measured for this system with liquid and metal field electrodes. For a system with an organic insulator, the range of variation of the surface potential from enrichment of the space-charge region of the semiconductor to the inversion state is first obtained without changing the mechanism of interaction between the adsorbed layer and the semiconductor surface. The effect of enhanced polarization of the space-charge region of the semiconductor occurs due to a change in the spatial structure of mobile charge in the organic dielectric layer. The system developed in the study opens up technological opportunities for the formation of a new generation of electronic devices based on organic film structures and for experimental modeling of the electronic properties of biological membranes.
Photoluminescence of amorphous and crystalline silicon nanoclusters in silicon nitride and oxide superlattices
摘要
The photoluminescence properties of silicon nitride and oxide superlattices fabricated by plasmaenhanced chemical vapor deposition are studied. In the structures annealed at a temperature of 1150°C, photoluminescence peaks at about 1.45 eV are recorded. The peaks are defined by exciton recombination in silicon nanocrystals formed upon annealing. Along with the 1.45-eV peaks, a number of peaks defined by recombination at defects at the interface between the nanocrystals and silicon-nitride matrix are detected. The structures annealed at 900°C exhibit a number of photoluminescence peaks in the range 1.3–2.0 eV. These peaks are defined by both the recombination at defects and exciton recombination in amorphous silicon nanoclusters formed at an annealing temperature of 900°C. The observed features of all of the photoluminescence spectra are confirmed by the nature of the photoluminescence kinetics.
Nucleation of two-dimensional islands on Si (111) during high-temperature epitaxial growth
摘要
The process of two-dimensional island nucleation at the surface of ultra large Si (111) during hightemperature epitaxial growth is studied by in situ ultrahigh-vacuum reflection electron microscopy. The critical terrace size Dcrit, at which a two-dimensional island is nucleated in the center, is measured in the temperature range 900–1180°C at different silicon fluxes onto the surface. It is found that the parameter Dcrit2 is a power function of the frequency of island nucleation, with the exponent χ = 0.9 ± 0.05 in the entire temperature range under study. It is established that the kinetics of nucleus formation is defined by the diffusion of adsorbed silicon atoms at temperatures of up to 1180°C and the minimum critical nucleus size corresponds to 12 silicon atoms.
Microcrystalline, Nanocrystalline, Porous, and Composite Semiconductors
Structural studies of ZnS:Cu (5 at %) nanocomposites in porous Al2O3 of different thicknesses
摘要
We present EXAFS, XANES, and X-ray diffraction data on nanoscale ZnS:Cu (5 at %) structures fabricated by the thermal deposition of a ZnS and Cu powder mixture in porous anodic alumina matrices with a pore diameter of 80 nm and thicknesses of 1, 3, and 5 μm. The results obtained are compared with data on ZnS:Cu films deposited onto a polycor surface. According to X-ray diffraction data, the samples contain copper and zinc compounds with sulfur (Cu2S and ZnS, respectively); the ZnS compound is in the cubic (sphalerite) and hexagonal (wurtzite) modifications. EXAFS and XANES studies at the K absorption edges of zinc and copper showed that, in samples deposited onto polycor and alumina with thicknesses of 3 and 5 μm, most copper atoms form the Cu2S compound, while, in the sample deposited onto a 1-μm-thick alumina layer, copper atoms form metallic particles on the sample surface. Copper crystals affect the Zn–S interatomic distance in the sample with a 1-μm-thick porous Al2O3 layer; this distance is smaller than in the other samples.
Carbon Systems
Thermal stability of hydrogenated small-diameter carbon nanotubes
摘要
The initial stage of hydrogen desorption from fully hydrogenated carbon nanotubes (3.0) and (2.2) is numerically studied by the molecular dynamics method. The temperature dependence of the desorption rate is directly determined at T = 1800–2500 K. The characteristic desorption times are determined at temperatures outside this range by extrapolation. It is shown that hydrogen desorption leads to the appearance of electronic states in the band gap.
On the theory of adsorption on graphene-like compounds
摘要
Based on a previously proposed model of the electronic spectrum of binary ANB8–N graphene-like compounds (GLC), adsorption theory is constructed, which allows determination of the role of the adatom level position, the adatom–substrate coupling constant, and the gap inherent to GLC in the free state with heteropolar bonds in the formation of the adatom electronic structure. The cases of free-standing and epitaxial GLCs on a metal surface are considered. In the case of free-standing GLCs, analysis shows local states mainly contribute to the adatom occupation number na at large and intermediate adatom–GLC coupling constants; as the coupling constants decrease, the contribution of the GLC valence band increases. The main feature of an epitaxial GLC on metal is the absence of a gap, hence, the contribution of adatom local states to na. Estimations show that changes in the adatom–substrate and GLC–metal coupling constants affect na in almost the same way. In this case, the dependence of na on the GLC gap is not critical from the qualitative viewpoint. Adsorption on the GLC–semiconductor structure is briefly discussed.
Physics of Semiconductor Devices
Analysis of the impact of non-1D effects on the gate switch-on current in 4H-SiC thyristors
摘要
The impact of non-1D effects caused by the spread of the gate current in the base layer on the gate switch-on current in 4H-SiC thyristors is considered. It is shown that a new switching mechanism implemented in 4H-SiC thyristors results in the dependence of the gate switch-on current on the thyristor parameters, with this dependence being fundamentally different from that in conventional silicon thyristors.
On the effect of ballistic overflow on the temperature dependence of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes
摘要
The dependences of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes on the temperature and excitation level are studied. The experiment is performed for two luminescence excitation modes. A comparison of the results obtained during photo- and electroluminescence shows an additional (to the loss associated with Auger recombination) low-temperature loss in the high-density current region. This causes inversion of the temperature dependence of the quantum efficiency at temperatures lower than 220–300 K. Analysis shows that the loss is associated with electron leakage from the light-emitting-diode active region. The experimental data are explained using the ballistic-overflow model. The simulation results are in qualitative agreement with the experimental dependences of the quantum efficiency on temperature and current density.
Electroluminescence of InAs/InAs(Sb)/InAsSbP LED heterostructures in the temperature range 4.2–300 K
摘要
The electroluminescence of InAs/InAsSbP and InAsSb/InAsSbP LED heterostructures grown on InAs substrates is studied in the temperature range T = 4.2–300 K. At low temperatures (T = 4.2–100 K), stimulated emission is observed for the InAs/InAsSbP and InAsSb/InAsSbP heterostructures with an optical cavity formed normal to the growth plane at wavelengths of, respectively, 3.03 and 3.55 μm. The emission becomes spontaneous at T > 70 K due to the resonant “switch-on” of the CHHS Auger recombination process in which the energy of a recombining electron–hole pair is transferred to a hole, with hole transition to the spin–orbit-split band. It remains spontaneous up to room temperature because of the influence exerted by other Auger processes. The results obtained show that InAs/InAs(Sb)/InAsSbP structures are promising for the fabrication of vertically emitting mid-IR lasers.
Increase the threshold voltage of high voltage GaN transistors by low temperature atomic hydrogen treatment
摘要
High-electron-mobility transistors (HEMTs) based on AlGaN/GaN epitaxial heterostructures are a promising element base for the fabrication of high voltage electronic devices of the next generation. This is caused by both the high mobility of charge carriers in the transistor channel and the high electric strength of the material, which makes it possible to attain high breakdown voltages. For use in high-power switches, normally off-mode GaN transistors operating under enhancement conditions are required. To fabricate normally off GaN transistors, one most frequently uses a subgate region based on magnesium-doped p-GaN. However, optimization of the p-GaN epitaxial-layer thickness and the doping level makes it possible to attain a threshold voltage of GaN transistors close to Vth = +2 V. In this study, it is shown that the use of low temperature treatment in an atomic hydrogen flow for the p-GaN-based subgate region before the deposition of gate-metallization layers makes it possible to increase the transistor threshold voltage to Vth = +3.5 V. The effects under observation can be caused by the formation of a dipole layer on the p-GaN surface induced by the effect of atomic hydrogen. The heat treatment of hydrogen-treated GaN transistors in a nitrogen environment at a temperature of T = 250°C for 12 h reveals no degradation of the transistor’s electrical parameters, which can be caused by the formation of a thermally stable dipole layer at the metal/p-GaN interface as a result of hydrogenation.
MSM optical detector on the basis of II-type ZnSe/ZnTe superlattice
摘要
On the basis of a type-II ZnSe/ZnTe superlattice, a MSM (metal—semiconductor–metal) photodetector is fabricated and investigated. The detector features low dark currents and a high sensitivity. The spectral characteristic of the detector provides the possibility of the selective detection of three separate spectral portions of visible and near-infrared radiation.
Specific features of waveguide recombination in laser structures with asymmetric barrier layers
摘要
The spatial distribution of the intensity of the emission caused by recombination appearing at a high injection level (up to 30 kA/cm2) in the waveguide layer of a GaAs/AlGaAs laser structure with GaInP and AlGaInAs asymmetric barrier layers is studied by means of near-field scanning optical microscopy. It is found that the waveguide luminescence in such a laser, which is on the whole less intense as compared to that observed in a similar laser without asymmetric barriers, is non-uniformly distributed in the waveguide, so that the distribution maximum is shifted closer to the p-type cladding layer. This can be attributed to the ability of the GaInP barrier adjoining the quantum well on the side of the n-type cladding layer to suppress the hole transport.
Spatial redistribution of radiation in flip-chip photodiodes based on InAsSbP/InAs double heterostructures
摘要
The spatial distribution of equilibrium and nonequilibrium (including luminescent) IR (infrared) radiation in flip-chip photodiodes based on InAsSbP/InAs double heterostructures (λmax = 3.4 μm) is measured and analyzed; the structural features of the photodiodes, including the reflective properties of the ohmic contacts, are taken into account. Optical area enhancement due to multiple internal reflection in photodiodes with different geometric characteristics is estimated.
Fabrication, Treatment, and Testing of Materials and Structures
Study of the structural and optical properties of GaP(N) layers synthesized by molecular-beam epitaxy on Si(100) 4° substrates
摘要
The structural and optical properties of GaP and GaPN layers synthesized by molecular-beam epitaxy on Si(100) substrates misoriented by 4° are studied. The possibility of producing GaP buffer layers that exhibit a high degree of heterointerface planarity and an outcropping dislocation density of no higher than ~2 × 108 cm–2 is shown. Emission from the Si/GaP/GaPN structure in the spectral range of 630–640 nm at room temperature is observed. Annealing during growth of the Si/GaP/GaPN structure makes it possible to enhance the room-temperature photoluminescence intensity by a factor of 2.6, with no shift of the maximum of the emission line.
The temperature dependence of the conductivity peak values in the single and the double quantum well nanostructures n-InGaAs/GaAs after IR-illumination
摘要
The dependences of the longitudinal and Hall resistances on a magnetic field in n-InGaAs/GaAs heterostructures with a single and double quantum wells after infrared illumination are measured in the range of magnetic fields В = 0–16 T and temperatures T = 0.05–4.2 K. Analysis of the experimental results was carried out on a base of two-parameter scaling hypothesis for the integer quantum Hall effect. The value of the second (irrelevant) critical exponent of the theory of two-parameter scaling was estimated.