Том 51, № 12 (2017)
- Жылы: 2017
- Мақалалар: 21
- URL: https://journals.rcsi.science/1063-7826/issue/view/12578
XXI International Symposium “Nanophysics and Nanoelectronics”, Nizhny Novgorod, March 13–16, 2017
On the band spectrum in p-type HgTe/CdHgTe heterostructures and its transformation under temperature variation
Аннотация
The magnetoabsorption and interband photoconductivity spectra of HgTe/CdHgTe quantum wells exhibiting p-type conductivity are studied at different temperatures. It is shown that, for a sample with a normal band structure, the long-wavelength edge of the spectra shifts to higher energies with temperature increase, indicating an increase of the band gap in the quantum well. For a sample with an inverted band structure, it is for the first time found that the long-wavelength cut-off shifts to lower energies due to the topological phase transition from the inverted band structure to the normal structure with temperature increase. The experimental data are in agreement with the results of theoretical band-structure calculations based on the Kane model.
Specific features of the photoexcitation spectra of epitaxial InN layers grown by molecular-beam epitaxy with the plasma activation of nitrogen
Аннотация
The results of studies of the photoexcitation spectra of epitaxial InN layers formed by molecular-beam epitaxy with the plasma activation of nitrogen are reported. The concentration of free charge carriers in the layers is 1018–1019 cm–3. The photoconductivity, photoluminescence, and absorption spectra exhibit a shift of the long-wavelength threshold of interband transitions in accordance with the Burstein–Moss effect for n-InN with different concentrations of equilibrium electrons. In the samples, absolute negative photoconductivity with a nanosecond relaxation time is observed. The results of photoelectric, absorption, and luminescence spectroscopy experiments are correlated with the technological parameters and electron microscopy data.
Selective etching of Si, SiGe, Ge and its usage for increasing the efficiency of silicon solar cells
Аннотация
Dependences of the etch rates for KOH and HF:H2O2:CH3COOH solutions on SiGe layer composition were investigated. The obtained results has been proposed to use for formation of the submicron relief on the silicon surface via selective etching of the structures with Ge(Si) self-assembled nanoislands. In the framework of the proposed approach the Ge(Si) nanoislands serve as a mask for selective etching of Si in a mixture of an aqueous solution of KOH with isopropyl alcohol, followed by the islands removal from the surface by the selective etching in HF:H2O2:CH3COOH. It was demonstrated experimentally that such approach allows to produce the submicron relief on a silicon surface, which leads to the significant decrease of the reflectivity in a wide spectral range. It is believed that the proposed method of surface relief formation can be used to improve the efficiency of the thin-film solar cells based on the crystalline silicon.
Manifestation of PT symmetry in the exciton spectra of quantum wells
Аннотация
The reflection and photoluminescence excitation spectra under circular polarization of the incident light are measured in wide quantum wells whose width is much larger than the exciton Bohr radius. It is found that, in the absence of a magnetic field, the relation between the intensities of even and odd absorption peaks is reversed upon reversal of the sign of circular polarization.
Antimony segregation in Si layers grown by molecular beam epitaxy on Si wafers with different crystallographic orientations
Аннотация
The segregation of Sb in Si layers grown by molecular beam epitaxy on Si substrates with the (111), (110), and (115) crystallographic orientations is studied; the results obtained for these orientations are compared with those obtained for the most widely used orientation (001). It is found that there is a qualitative similarity between the temperature dependences of the Sb segregation ratio (r) for all studied orientations; in particular, it is possible to separate two characteristic temperature ranges corresponding to the kinetically limited and equilibrium regimes of segregation. However, quantitatively, the values of r for the orientations under study differ significantly from those for the Si(001) case at the same temperatures. For all orientations, narrow temperature ranges within which the values of r vary by nearly five orders of magnitude are revealed for all dependences of r on the growth temperature. This finding allows us to adopt the method of selective doping, which was for the first time suggested by us for structures grown on Si (001) and is based on the controlled use of the segregation effect, to structures grown on Si substrates with an orientation different from (001). Using this method, selectively doped Si:Sb/Si(111) structures are fabricated; in these structures, a variation in the Sb concentration by an order of magnitude occurs at the scale of several nanometers.
Investigation of HgCdTe waveguide structures with quantum wells for long-wavelength stimulated emission
Аннотация
The photoluminescence and stimulated emission during interband transitions in quantum wells based on HgCdTe placed in an insulator waveguide based on a wide-gap CdHgTe alloy are studied. Heterostructures with quantum wells based on HgCdTe are of interest for the development of long-wavelength lasers in the range of 25–60 μm, which is currently unattainable for quantum-cascade lasers. Optimal designs of quantum wells for attainment of long-wavelength stimulated emission under optical pumping are discussed. It is shown that narrow quantum wells from pure HgTe appear to be more promising for long-wavelength lasers in comparison with wide (potential) wells from the alloy due to the suppression of Auger recombination. It is demonstrated that molecular-beam epitaxy makes it possible to obtain structures for the localization of radiation with a wavelength of up to 25 μm at a high growth rate. Stimulated emission is obtained for wavelengths of 14–6 μm with a threshold pump intensity in the range of 100–500 W/cm2 at 20 K.
Activation conductivity in HgTe/CdHgTe quantum wells at integer Landau level filling factors: Role of the random potential
Аннотация
Shubnikov-de Haas oscillations are studied in 8-nm-wide HgTe/CdHgTe quantum wells with an electron concentration of (1.7–13) × 1011 cm–2 in the temperature range from 1.6 to 40 K. The gaps between Landau levels and the quantum relaxation time are determined from the temperature dependence of the oscillation amplitude at integer filling factors. The experimental gap values are found to be in good agreement with the results of the single-particle calculation of the level energies using the 8-band Kane model. The experimental widths of the density of states are indicative of profound screening of the exchange interaction in HgTe/CdHgTe quantum wells.
Electronic Properties of Semiconductors
Radiation-produced defects in germanium: Experimental data and models of defects
Аннотация
The problem of radiation-produced defects in n-Ge before and after n → p conversion is discussed in the light of electrical data obtained by means of Hall effect measurements as well as Deep Level Transient Spectroscopy. The picture of the dominant radiation defects in irradiated n-Ge before n → p conversion appears to be complicated, since they turn out to be neutral in n-type material and unobserved in the electrical measurements. It is argued that radiation-produced acceptors at ≈EC – 0.2 eV previously ascribed to vacancy-donor pairs (E-centers) play a minor role in the defect formation processes under irradiation. Acceptor defects at ≈EV + 0.1 eV are absolutely dominating in irradiated n-Ge after n → p conversion. All the radiation defects under consideration were found to be dependent on the chemical group-V impurities. Together with this, they are concluded to be vacancy-related, as evidenced positron annihilation experiments. A detailed consideration of experimental data on irradiated n-Ge shows that the present model of radiation-produced defects adopted in literature should be reconsidered.
Study and simulation of electron transport in Ga0.5ln0.5Sb based on Monte Carlo method
Аннотация
This work addresses the issue related to the electronic transport in the III–V ternary material Ga0.5ln0.5Sb using Monte Carlo method. We investigated the electronic motion in the three valleys Γ, L, and X of the conduction band. These three valleys are isotropic, non-parabolic and centred on the first Brillouin zone. In our study, we included scatterings with ionised impurities, acoustic and polar optical phonons, as well as, intervalley and intravalley interactions. We discussed the electronic transport characteristics at the stationary and the transient regimes in function of temperature and electric field.
Surfaces, Interfaces, and Thin Films
Production and identification of highly photoconductive CdSe-based hybrid organic-inorganic multi-layer materials
Аннотация
Highly photoconductive thin multi-layers of new hybrid organic-inorganic semiconductors have been developed. They result by the combination of an inorganic semiconductor with ferrocene, a commercially available compound, applying the electrodeposition and spin coating techniques, introducing sodium oxalate as an additive in the electrolytic bath. The organic layer of the hybrid system is enveloped between two inorganic layers in a sandwich-like structure. The full characterization of the final products by XRD, SEM-EDAX, band gap and photo electro chemical cell (PEC) measurements confirmed the development of the hybrid semiconducting system. The outer electrodeposited CdSe layer of the sandwich-like materials exhibits a definite hexagonal structure, whereas, as derived from the XRD and band gap data, the development of a new semiconducting compound has been confirmed. Thus, due to a synergic action, the three-layer materials present a remarkably improved photoresponse compared to that of the pure cubic CdSe electrodeposited in the presence of the oxalate additive as well as the three-layer hybrid CdSe-based products developed in our previous work in additive-free electrolytic baths.
Effect of Ag in CdSe thin films prepared using thermal evaporation
Аннотация
It has been a general practice to dope thin films with suitable dopants to modify the properties of the films to make them more suitable for potential applications. When the dopant concentrations are low, they do not normally affect the structure and morphology of the films. However, it may lead to drastic changes in electronic properties of the films. This might result from the dopant getting incorporated into the lattice of the material of the films. Cadmium selenide is an important compound semiconductor material with an attractive energy band gap. The present work relates to an attempt made to dope CdSe thin films with silver. CdSe:Ag (1–5%) thin films were deposited on glass substrates at an optimized substrate temperature of 453 K using thermal evaporation technique. The grown films were analyzed using X-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) techniques. It is observed that undoped CdSe thin films and CdSe:Ag films have hexagonal structure. The grain size was found to increase marginally with an increase in the Ag concentration. The optical band gap of the films determined by optical transmission measurements agree with that of CdSe. Electrical conductivity is observed to increase from 10–4 to 3.66 (Ω cm)–1 on addition of silver. The variation of resistance with temperature indicates that the prepared films consist of CdSe and Ag existing as two separate phases coexisting and contributing individually to the resistivity of the films.
Al-doped and pure ZnO thin films elaborated by sol–gel spin coating process for optoelectronic applications
Аннотация
Pure and aluminum-doped zinc oxide thin films were grown by spin coating at room temperature. As a starting material, zinc acetate was used. The dopant source was aluminum nitrate; the dopant molar ratio was varied between 1 and 10%. Structural analysis reveals that all films consist of single hexagonal wurtzite phase ZnO, and a preferential orientation along c-axis. They have a homogeneous surface. The measurements show that the films are nanostructured. The transmittance is greater than 75% in the visible region. The band gap energy decreases with the addition of dopant (Al) in prepared thin films and the resistivity decreases significantly.
Effect of high voltage electric field on structure and property of PEDOT:PSS film
Аннотация
Low electrical conductivity of PEDOT:PSS film is to some extent a limit for its wide application. To solve this problem, the high voltage electric field was used to improve the film’s electrical conductivity and its effects on the film’s structure and properties were investigated. The PEDOT:PSS film was prepared on quartz substrate with spin coating. Visible light transmittance of the prepared film was tested with UV–Visible spectroscopy and chemical structure was measured with Fourier transform Raman spectroscopy (FIRM). The surface morphology was characterized with AFM, and electrical conductivity was measured with Hall effects measurement. The results showed that with the increase of the electric field, the electrical conductivity of PEDOT:PSS film was boosted rapidly at first, and then improved slowly when the electric field was above 200 kV/m. The film’s electrical conductivity improved more than 17 times in total from 0.51 × 10–3 up to 8.92 × 10–3 S/m. However, the film’s visible light transmittance decreased only a little with the increase of the electric field, not more than 3%. In addition, despite little change in the chemical structure of the PEDOT:PSS film, its surface roughness increased significantly with the increase of the electric field intensity.
A comparative study on the electronic and optical properties of Sb2Se3 thin film
Аннотация
The thin film of Sb2Se3 was deposited by thermal evaporation method and the film was annealed in N2 flow in a three zone furnace at a temperature of 290°С for 30 min. The structural properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (ТЕМ), X-ray diffraction (XRD) and Raman spectroscopy, respectively. It is seen that the as-deposited film is amorphous and the annealed film is polycrystalline in nature. The surface of Sb2Se3 film is oxidized with a thickness of 1.15 nm investigated by X-ray photolecetron spectroscopy (XPS) measurement. Spectroscopic ellipsometry (SE) and UV–vis spectroscopy measurements were carried out to study the optical properties of Sb2Se3 film. In addition, the first principles calculations were applied to study the electronic and optical properties of Sb2Se3. From the theoretical calculation it is seen that Sb2Se3 is intrinsically an indirect band gap semiconductor. Importantly, the experimental band gap is in good agreement with the theoretical band gap. Furthermore, the experimental values of n, k, ε1, and ε2 are much closer to the theoretical results. However, the obtained large dielectric constants and refractive index values suggest that exciton binding energy in Sb2Se3 should be relatively small and an antireflective coating is recommended to enhance the light absorption of Sb2Se3 for thin film solar cells application.
Semiconductor Structures, Low-Dimensional Systems, and Quantum Phenomena
Charge density at the Al2O3/Si interface in Metal–lnsulator–Semiconductor devices: Semiclassical and quantum mechanical descriptions
Аннотация
In this paper, a quantum correction computation of the inversion layer of charge density was investigated. This study is carried out for a one-dimensional Metal–lnsulator–Semiconductor (MIS) structure with (100) oriented P-type silicon as substrate. The purpose of this paper is to point out the differences between the semiclassical and quantum-mechanical charge description at the interface Al2O3/Si, and to identify some electronic properties of our MIS device using different thickness of the high-k oxide and diverse temperature with different carrier statitics (Fermi–Dirak statitics and Boltzmann statitics). In particular, the calculations of capacitance voltage (C–V), sheet electron density, a relative position of subband energies and their wave functions are performed to examine qualitatively and quantitatively the electron states and charging mechanisms in our device.
Morphological and spectroscopic studies on the vertically aligned zinc oxide nanorods grown on low and high temperature deposited seed layer
Аннотация
Vertically aligned zinc oxide nanorods were grown on low and high temperature deposited aluminium doped zinc oxide seed layer by hydrothermal method and annealed to improve crystallinity. The morphology of the seed layer and the grown nanorods were studied by field emission scanning electron microscopy characterization technique. The properties of the zinc oxide nanorods were analyzed using laser spectroscopic studies. Resonant Raman spectroscopy reveals the unique increase in the A1(LO) mode of vibration with increase in count. The luminescence property of the nanorods was studied with photoluminescence spectrometer. The vertically aligned zinc oxide nanorods show, the very high band edge emission in the ultraviolet region of the electromagnetic spectrum.
Physics of Semiconductor Devices
Electrical properties and the determination of interface state density from I–V, C–f and G–f measurements in Ir/Ru/n-InGaN Schottky barrier diode
Аннотация
The electrical properties of the Ir/Ru Schottky contacts on n-InGaN have been investigated by current-voltage (I–V), capacitance-voltage (C–V), capacitance-frequency (C–f) and conductance-frequency (G–f) measurements. The obtained mean barrier height and ideality factor from I–V are 0.61 eV and 1.89. The built-in potential, doping concentration and barrier height values are also estimated from the C–V measurements and the corresponding values are 0.62 V, 1.20 × 1017 cm–3 and 0.79 eV, respectively. The interface state density (NSS) obtained from forward bias I–V characteristics by considering the series resistance (RS) values are lower without considering the series resistance (RS). Furthermore, the interface state density (NSS) and relaxation time (τ) are also calculated from the experimental C–f and G–f measurements. The NSS values obtained from the I–V characteristics are almost three orders higher than the NSS values obtained from the C–f and G–f measurements. The experimental results depict that NSS and τ are decreased with bias voltage. The frequency dependence of the series resistance (RS) is attributed to the particular distribution density of interface states.
Performance characteristics of p-channel FinFETs with varied Si-fin extension lengths for source and drain contacts
Аннотация
The length of Source/Drain (S/D) extension (LSDE) of nano-node p-channel FinFETs (pFinFETs) on SOI wafer influencing the device performance is exposed, especially in drive current and gate/S/D leakage. In observation, the longer LSDEpFinFET provides a larger series resistance and degrades the drive current (IDS), but the isolation capability between the S/D contacts and the gate electrode is increased. The shorter LSDE plus the shorter channel length demonstrates a higher trans-conductance (Gm) contributing to a higher drive current. Moreover, the subthreshold swing (S.S.) at longer channel length and longer LSDE represents a higher value indicating the higher amount of the interface states which possibly deteriorate the channel mobility causing the lower drive current.
Single electron transistor: Energy-level broadening effect and thermionic contribution
Аннотация
In this paper, a theoretical study of single electron transistor (SET) based on silicon quantum dot (Si–QD) has been studied. We have used a novel approach based on the orthodox theory. We studied the energy–level broadening effect on the performance of the SET, where the tunnel resistance depends on the discrete energy. We have investigated the I–V curves, taking into account the effects of the energy-level broadening, temperature and bias voltage. The presence of Coulomb blockade phenomena and its role to obtain the negative differential resistance (NDR) have been also outlined.
Fabrication, Treatment, and Testing of Materials and Structures
Patterning approach for detecting defect in device manufacturing
Аннотация
Compact handheld devices which were a dream in the past are now a reality; this has been enabled by miniaturization of circuit architectures including power devices. Scaling down of the design feature sizes does come with a price with an increase in systematic defects during chip manufacturing. There are generally two methods of inline defect detection adopted to monitor the semiconductor device fabrication—optical inspection and electron beam inspection. The optical inspection uses ultra-violet and deep ultra-violet (UV/DUV) light to find patterning defects on the wafer. While the electron-beam inspection uses electron charge and discharge measurement to find electrical connection defects, both are a costly procedure in terms of resources and time. The physical limit of feature resolution of the optical source is now making the defect inspection job difficult in miniaturized application specific integrated circuit (ASIC). This study is designed to test the patterning optimization approach on both inspection platforms. Using hotspot analysis weak locations are identified in the full chip design, and then they are verified in the inline wafer inspection. The criterion for hot-spot determination is also discussed in this paper.
The effects of electron irradiation and thermal dependence measurements on 4H-SiC Schottky diode
Аннотация
In this paper the effects of high energy (3.0 MeV) electrons irradiation over a dose ranges from 6 to 15 MGy at elevated temperatures 298 to 448 K on the current-voltage characteristics of 4H-SiC Schottky diodes were investigated. The experiment results show that after irradiation with 3.0 MeV forward bias current of the tested diodes decreased, while reverse bias current increased. The degradation of ideality factor, n, saturation current, Is, and barrier height, Φb, were not noticeable after the irradiation. However, the series resistance, Rs, has increased significantly with increasing radiation dose. In addition, temperature dependence current-voltage measurements, were conducted for temperature in the range of 298 to 448 K. The Schottky barrier height, saturation current, and series resistance, are found to be temperature dependent, while ideality factor remained constant.