On the thermoelectric properties and band gap of silicon–germanium alloys in the high-temperature region

For n- and p-type Si_0.85Ge_0.15 alloys, the thermoelectric properties (thermopower, resistivity, thermal conductivity, and thermoelectric efficiency) are determined in the range from room temperature to 1200°C. The measurements are carried out with an upgraded device [1] by absolute and steady-state methods with thermal screens. The device is upgraded to extend the working-temperature range to ~1500 K. On the basis of these data, the energy-related capabilities of the alloy are estimated; the thermal band-gap width is calculated in the temperature range of ~1300–1400 K.     

3-D simulation of angled strike heavy-ion induced charge collection in silicon–germanium heterojunction bipolar transistors

This paper presents 3-D simulation of angled strike heavy-ion induced charge collection in domestic silicon-germanium heterojunction bipolar transistors （SiGe HBTs）. 3D damaged model of SiGe HBTs single-event effects （SEE） is built by TCAD simulation tools to research ions angled strike dependence. We select several different strike angles at variously typical ions strike positions. The charge collection mechanism for each terminal is identified based on analysis of the device structure and simulation results. Charge collection induced by angled strike ions presents a complex situation. Whether the location of device ions enters, as long as ions track through the sensitive volume, it will cause vast charge collection. The amount of charge collection of SiGe HBT is not only related to length of ions track in sensitive volume, but also influenced by STI and distance between ions track and electrodes. The simulation model is useful to research the practical applications of SiGe HBTs in space, and provides a theoretical basis for the further radiation hardening.     

Formation of electrically active centers in silicon irradiated with electrons and then annealed at temperatures of 400–700°C

The effect of irradiation with electrons on the formation of quenched-in donors in silicon is studied. It is found that n-and p-type regions are formed in the bulk of single-crystal silicon as a result of irradiation with electrons and subsequent annealing at a temperature of 450°C. The concentration of charge carriers in the regions of both types increases as the radiation dose and the annealing duration increase, which indicates that not only quenched-in donors but also quenched-in acceptors are formed. Nonuniformity in the distribution of the acceptor and donor centers correlates with fluctuations of the oxygen concentration in silicon.     

Specific features of the current–voltage characteristics of SiO2/4H-SiC MIS structures with phosphorus implanted into silicon carbide

The effect of phosphorus implantation into a 4H-SiC epitaxial layer immediately before the thermal growth of a gate insulator in an atmosphere of dry oxygen on the reliability of the gate insulator is studied. It is found that, together with passivating surface states, the introduction of phosphorus ions leads to insignificant weakening of the dielectric breakdown field and to a decrease in the height of the energy barrier between silicon carbide and the insulator, which is due to the presence of phosphorus atoms at the 4H-SiC/SiO₂ interface and in the bulk of silicon dioxide.     

Negative photoconductivity in films of alloys of II–VI compounds

Various negative photoelectric effects in films of alloys of II–VI compounds deposited from a solution are studied depending on the deposition mode and heat treatment. A combined electronic-molecular mechanism of the negative photocapacitance effect, which is for the first time found in Cd_{1 ? x} Zn _x S and CdS_{1 ? x} Se _x films, and negative slowly relaxing photoelectric effects is established. The latter are caused by the transition of electrons arranged in a nanoscale surface layer from shallow energy levels of attachment centers to deeper levels with lower polarizability and by the presence of nanoscale clusters playing the role of a “reservoir” for minority carriers in these materials. A model, which makes it possible to interpret the main regularities of negative photoconductivity in Cd_{1 ? x} Zn _x S and CdS_{1 ? x} Se _x films deposited from a solution, is suggested. It is established that the negative residual photoconductivity is explained on the basis of a double barrier profile, while the negative differential photoconductivity is explained by the presence of nanoscalel electric domains.     

Photoelectric characteristics of silicon carbide–silicon structures grown by the atomic substitution method in a silicon crystal lattice

Data obtained in an experimental study of the photoelectric characteristics of silicon–silicon carbide structures grown by the atomic substitution method on silicon (100) and (111) substrates are presented. It is found that the maximum sunlight conversion efficiency of a silicon–silicon carbide (silicon carbide–silicon) heterojunction is 5.4%. The theory of dilatation dipole formation upon synthesis by the atomic substitution method is used to account for the mechanism of electrical barrier formation at the silicon–silicon carbide interface.     

Impact ionization of shallow donor states in germanium, 4–7°K

The electron concentration/field characteristic n(E) is calculated for pure samples of n-germanium in good agreement with experimental results. The kinetic theory is developed in the language of the sticking probabilities P_i of Lax, but generalised to include impact-dependent P_i, and shows that, as well as capture occurring by a cascade process, ionization (impact or otherwise) occurs by inverse cascade. A breakdown regime is identified in which, with allowance for the inverse cascade, the usual Price breakdown criterion is applicable; but a new, non-Price, regime is shown to be a result of the impact dependence of the P_i. The border between the regimes is marked by a strongly temperature dependent sample compensation ratio, the samples considered lying in the new regime at 7°K. S-breakdown in a Price regime is seen as a natural consequence of the impact dependence of the P_i. The non-Maxwellian distribution functions used were of Stratton or equipartition form, or an appropriately defined mixture of the two; the effect of their variation on the calculated results was studied. Inclusion of Maxwellian distributions showed Kurosawa's S-breakdown theory to be untenable for E

6 V/cm. Some additional scattering mechanism appears at high values of n. Conduction band anisotropy was taken into account; the donor levels were not supposed hydrogenic. No appeal was made to the principle of detailed balance.     

1.5–1.6 μm photoluminescence of silicon layers with a high density of lattice defects

This study is concerned with photoluminescence of nanostructured silicon layers that emit radiation in the wavelength range 1.5–1.6 μm due to optical transitions to deep levels of recombination centers produced by crystal lattice defects. It is shown that the dependence of the photoluminescence intensity on the excitation power density is adequately described by the model of deep levels of one type. A shift of the photoluminescence peak to shorter wavelengths with increasing excitation power density is observed. The shift is indicative of changes in the occupancy of deep levels in the conditions of transfer of charge carriers between recombination centers.     

Formation and “white” photoluminescence of nanoclusters in SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films implanted with carbon ions

Experimental data on ion synthesis of nanocomposite layers with carbon-rich clusters and silicon nanocrystals by irradiation of nonstoichiometric silicon oxide (SiO _x ) films with carbon ions followed by high-temperature annealing are reported. It is shown that, at rather high doses of C⁺ ions, the resulting films exhibit photoluminescence with a spectrum that encompass the entire visible and near-infrared regions. The formation of carbon-rich clusters and silicon nanocrystals is confirmed by X-ray photoelectron spectroscopy data. The distribution of carbon practically reproduces the calculated profile of ion ranges, suggesting that there is no noticeable diffusive redistribution of carbon. A qualitative model of the layered structure of ion-synthesized structures is suggested.     

Generation of surface electron states with a silicon–ultrathin-oxide interface under the field-induced damage of metal–oxide–semiconductor structures

The high-frequency capacitance–voltage characteristics of metal–oxide–semiconductor structures on n-Si substrates with an oxide thickness of 39 Å are studied upon being subjected to damage by field stress. It is shown that the action of a high, but pre-breakdown electric field on an ultrathin insulating layer brings about the formation of a large number of additional localized interface electron states with an energy level arranged at 0.14 eV below the conduction band of silicon. It is found that, as the field stress is increased, the recharging of newly formed centers provides the accumulation of excess charge up to 8 × 10¹² cm^–2 at the silicon–oxide interface. The lifetime of localized centers created under field stress is two days, after which the dependences of the charge localized at the semiconductor–insulator interface on the voltage at the gate after and before field stress are practically the same.     

Current dependence of capacitance of germanium p +-p junctions in the temperature range of 290–330 K

The current dependence of differential capacitance of germanium p ⁺-p junctions with the p-region resistivity of 45, 30, and 10 Ω cm is investigated in the temperature range of 290–350 K. It is shown that the current dependence of the p ⁺-p-junction capacitance varies with an increasing junction temperature. At the temperature of 290 K, the capacitance decreases with an increasing reverse current, changes sign from positive to negative, and increases with the forward current. At 330 K, the capacitance decreases to the lowest positive value with an increasing reverse current and changes sign to negative with increasing the forward current. At 310 K, the p ⁺-p-junction capacitance can change the sign from positive to negative with increasing the forward and reverse current. It is assumed that the positive and negative p ⁺-p-junction capacitance is caused by the change in the junction-region charge by the external voltage.     

Specific features of photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from monosilane–hydrogen mixture

Photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from a monosilane-hydrogen mixture have been studied at a fraction of hydrogen in the mixture that corresponds to the onset of formation of a nanocrystalline phase in the structure of the films obtained. A behavior untypical of amorphous hydrogenated silicon films is observed for the photoconductivity and the spectral dependence of the absorption coefficient. The temperature dependences of the photoconductivity in the films under study are found to vary with the energy of incident photons. At a photon energy of 1.3 eV, temperature quenching of photoconductivity is observed. Prolonged illumination of the films led to a certain decrease in the absorption coefficient at photon energies in the range 1.2–1.5 eV. The results obtained are attributed to the possible presence of silicon nanocrystals in the structure of the films and to the influence of these nanocrystals on their photoelectric and optical properties.     

Formation and study of <Emphasis Type="Italic">p–i–n</Emphasis> structures based on two-phase hydrogenated silicon with a germanium layer in the <Emphasis Type="Italic">i</Emphasis>-type region

Four pairs of p–i–n structures based on polymorphous Si:H (pm-Si:H) are fabricated by the method of plasma-enhanced chemical vapor deposition. The structures in each pair are grown on the same substrate so that one of them does not contain Ge in the i-type layer while the other structure contains Ge deposited by molecular-beam epitaxy as a layer with a thickness of 10 nm. The pair differ from one another in terms of the substrate temperature during Ge deposition; these temperatures are 300, 350, 400, and 450°C. The data of electron microscopy show that the structures formed at 300°C contain Ge nanocrystals (nc-Ge) nucleated at nanocrystalline inclusions at the pm-Si:H surface. The nc-Ge concentration increases as the temperature is raised. The study of the current–voltage characteristics show that the presence of Ge in the i-type layer decreases the density of the short-circuit current in p–i–n structures when they are used as solar cells, whereas these layers give rise to an increase in current at a reverse bias under illumination. The obtained results are consistent with known data for structures with Ge clusters in Si; according to these data, Ge clusters increase the coefficient of light absorption but they also increase the rate of charge-carrier recombination.     

IR photodetectors in the range of λ = 1.5–8 μm, based on silicon with multicharged nanoclusters of manganese atoms

It is demonstrated that infrared photodetectors based on silicon with multicharged nanoclusters of manganese atoms can be designed that operate in the wavelength range of ?? = 1.55?C8 ??m. Photodetectors fabricated on such materials have the following parameters: a spectral sensitivity range of ?? = 1.55?C8 ??m, an operating temperature range of T = 77?C250 K, an optimal electric field of E = 5 V/cm, an optimal size of V = 3 × 2 × 1 mm³, a sensitivity threshold of S = 10^?9 W/cm², and a response time of ?? < 10^?6 s.     

Recent progress in epitaxial growth of III–V quantum-dot lasers on silicon substrate

In the past few decades, numerous high-performance silicon (Si) photonic devices have been demonstrated. Si, as a photonic platform, has received renewed interest in recent years. Efficient Si-based III–V quantum-dot (QDs) lasers have long been a goal for semiconductor scientists because of the incomparable optical properties of III–V compounds. Although the material dissimilarity between III–V material and Si hindered the development of monolithic integrations for over 30 years, considerable breakthroughs happened in the 2000s. In this paper, we review recent progress in the epitaxial growth of various III–V QD lasers on both offcut Si substrate and on-axis Si (001) substrate. In addition, the fundamental challenges in monolithic growth will be explained together with the superior characteristics of QDs.     

Drop impact reliability of Sn–1.0Ag–0.5Cu BGA interconnects with different mounting methods

The poor drop-shock resistance of near-eutectic Sn–Ag–Cu (SAC) solder interconnects drives the research and application low-Ag SAC solder alloys, especially for Sn–1.0Ag–0.5Cu (SAC105). In this work, by dynamic four-point bend testing, we investigate the drop impact reliability of SAC105 alloy ball grid array (BGA) interconnects with two different surface mounting methods: near-eutectic solder paste printing and flux dipping. The results indicate that the flux dipping method improves the interconnects failure strain by 44.7% over paste printing. Further mechanism studies show the fine interfacial intermetallic compounds (IMCs) at the printed circuit board side and a reduced Ag content inside solder bulk are the main beneficial factors overcoming other negative factors. The flux dipping SAC105 BGA solder joints possess fine Cu₆Sn₅ IMCs at the interface of solder/Cu pads, which increases the bonding strength between the solder/IMCs and the fracture resistance of the IMC grains themselves. Short soldering time of flux dipping joints above the solder alloy liquidus mitigates the growth of interfacial IMCs in size. In addition, a reduced Ag content in flux dipping joint bulk causes a low hardness and high compliance, thus increasing fracture resistance under higher-strain rate conditions.     

Formation mechanism of contact resistance to III–N heterostructures with a high dislocation density

The temperature dependences of the contact resistance ρ _c (T) of ohmic Pd-Ti-Pd-Au contacts to n-GaN and n-AlN wide-gap semiconductors with a high dislocation density are studied. The dependences ρ _c (T) for both contacts contain portions of exponential decrease ρ _c (T) and very weak dependence ρ _c (T) at higher temperatures. Furthermore, a plateau portion ρ _c (T) is observed in the low-temperature region for the Au-Pd-Ti-Pd-n-GaN contact. This portion appears only after rapid thermal annealing (RTA). In principle, the appearance of the plateau portion can be associated with preliminary heavy doping of the near-contact region with a shallow donor impurity and with doping during contact fabrication as a result of RTA, if the contact-forming layer contains a material that is a shallow donor in III–N. The dependences obtained are not explained by existing charge-transport mechanisms. Probable mechanisms explaining the experimental dependences ρ _c (T) for ohmic contacts to n-GaN and n-AlN are proposed.     

Special features of the electrical conductivity in doped α-Si:H films with silicon nanocrystals

The electrical properties of undoped and phosphorus-doped α-Si:H films with Si nanocrystals are studied. The silicon nanocrystals are formed by a solid-solid phase transition resulting from the nanosecond effect of a XeCl excimer laser on an amorphous film. The formation of the nanocrystals in the undoped films is accompanied by an increase in the electrical conductivity by two to three orders of magnitude and a simultaneous decrease in the effective activation energy of the conductivity from 0.7 to 0.14 eV. The nanocrystal sizes range from 2 to 10 nm for various laser treatment modes and are determined from Raman scattering data and high-resolution electron microscopy. The temperature dependence of the Fermi level is obtained by calculating the energies of the localized states of electrons and holes in the nanocrystals. It is shown that, as the temperature decreases, the Fermi level tends to the energy of the states in the Si nanocrystals for a wide concentration range of the dopant. The Fermi level’s location close to the states in the nanocrystals is a consequence of the fact that these states are multicharged. It is found that phosphorus effectively transforms into an electrically active state during laser treatment of the doped amorphous Si films, which is an important consideration in the fabrication of shallow p-n junctions and contacts for amorphous Si films.     

Formation of Weighting Coefficients in an Artificial Neural Network Based on the Memristive Effect in Metal–Oxide–Metal Nanostructures

An approach to formation and training of an artificial neural network (ANN) based on thin-film memristive metal–oxide–metal nanostructures, which exhibit the effect of bipolar resistive switching, has been proposed. An experimental electric circuit of a small-sized ANN (a two-layer perceptron with 32 memristive elements) has been constructed. An algorithm for formation of weighting coefficients (ANN training), which takes into account probable spread of technological parameters of memristive structures has been developed.