Local emission spectroscopy of surface micrograins in A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductors

The density-of-states spectra and the parameters of levels of electron states in locally chosen surface micrograins of indium antimonide and arsenide and gallium arsenide are studied with a tunneling electron microscope in the field-emission mode of measurements. By correlating the current–voltage characteristics with the formula for the probability of emission via levels, the activation energies of the levels (ψ) and the lifetimes of electrons at the levels (τ) are determined. Two types of levels for electron localization are identified. These are levels in the micrograin bulk (ψ ≈ 0.75, 1.15, and 1.59 eV for n-InSb, n-InAs, and n-GaAs, respectively; τ ~ 10^–8–10^–7 s) and in the surface region of an i-InSb micrograin (ψ ~ 0.73, 1.33, 1.85, 2.15, 5.1 eV; τ ≈ 5 × 10^–8–3 × 10^–7 s). A physical model involving the Coulomb-interaction-induced localization of light electrons and their size quantization determined by the electron effective mass, energy, and concentration and by the surface curvature of the micrograin is proposed.     

Cathodoluminescence of laser A<Superscript>II</Superscript>B<Superscript>VI</Superscript> heterostructures

A Cathodoluminescence (CL) method has been used for studies of ZnSe-based heterostructures with a CdSe fractional-monolayer recombination region. Electron beams with energies of 1–25 keV provide the ability to analyze CL bands associated with different layers of the heterostructure and revealed on the CL spectrum at different electron-beam penetration depth. Comparative analysis of the CL bands both from the recombination region and the upper layers has been used to characterize the transport properties of the structure. The correlation between the density and size distribution of quantum dots and full width at half maximum and spectral position of the CL bands has been studied in detail. The text was submitted by the authors in English.     

Photosensitivity of thin films of semiconductor nanocomposites based on metal-organic complexes with Cu<Superscript>+</Superscript> and Ru<Superscript>2+</Superscript>

The photosensitivity of nanocomposites in a system constituted by an organic transition metal complex and silica was studied. It is shown that the photosensitivity of a nanocomposite is determined by the valence and the ionization potential of the metal atom, which is equal to (3–8)×10⁴ cm²/J (quantum yield of carrier photogeneration is 0.03–0.05) for the Cu⁺ complex and 5×10³ cm²/J for the Ru²⁺ complex. The possibility of controlling the magnitudes and spectra of both the photosensitivity and luminescence of thin films of nanocomposites based on these complexes by varying the structure of metal complexes and the fact that the quantum efficiency of photogeneration can be raised by introducing transport molecules into the structure of a nanocomposite gives reason to believe that photosensitive and electroluminescent devices can be created on the basis of these nanocomposites.     

Development of nuclear radiation detectors based on epitaxially grown thick CdTe layers on n<Superscript>+</Superscript>-GaAs substrates

A CdTe/n⁺-GaAs heterojunction diode for a room-temperature nuclear radiation detector has been developed and demonstrated. The heterojunction diode was fabricated by growing a 2–5-μm-thick iodine-doped n-CdTe buffer layer on the n⁺-GaAs substrates, followed by about 100-μm-thick undoped p-like single crystalline CdTe layer using metalorganic vapor-phase epitaxy. The n-type buffer layer was found to be essential to improve the junction property of the diode detector. The diode detectors exhibited good rectification property and had the reverse leakage currents typically from 1 μA/cm² to 5 μA/cm² at 40 V bias. The detector clearly demonstrated its energy resolution capability by resolving the 59.54-keV gamma peak from the ²⁴¹Am radioisotope during the radiation detection test.     

Influence of Indirect Transitions on Optical Characteristics of A<Subscript>3</Subscript>B<Subscript>5</Subscript> Heteroepitaxial Layers

The influence of indirect transitions of Г-L and Г-Х types in the Brillouin zone on optical and electrophysical characteristics of heteroepitaxial layers of А₃В₅ compounds is estimated by the example of ternary (InGaAs) and quaternary (InGaAsP) compounds. It has been found that consideration of indirect transitions lowers the refractive index of semiconductor compounds by up to 15% in a narrow wavelength range of 0.4—0.6 μm.     

Effect of potential fluctuations on the energy structure of GaAs/AlGaAs quantum wells with A<Superscript>+</Superscript> centers

The transformation of photoluminescence spectra associated with A⁺ centers in GaAs/AlGaAs quantum wells due to changes in the pumping level and temperature is analyzed. It is shown that an important part in the formation of the energy structure of the system of GaAs/AlGaAs quantum wells is played by electrostatic potential fluctuations responsible for the spatial redistribution of charge and the appearance of free holes.     

Molecular state of <Emphasis Type="Italic">A</Emphasis><Superscript>+</Superscript> centers in GaAs/AlGaAs quantum well

Along with the separate A ⁺ centers in the GaAs/AlGaAs quantum wells, there exist paired molecular states of the centers. The molecular states manifest themselves as the second peak of photoluminescence associated with the A ⁺ centers. This statement is based on data on the specific features of circular-polarized photoluminescence and on the characteristic dependences of the amplitudes of photoluminescence peaks on the degree of doping and temperature. The binding energy of holes in the molecular states is determined. It is suggested that the paired state of two positively charged A ⁺ centers is possible due to the polaron effect.     

Experimental research on transient radiation effects in microprocessors based on SPARC-V8 architecture

An experimental system is developed for the transient radiation effects testing of an anti-radiation hardened processor. Based on this system, the transient radiation effects in a microprocessor based on SPARC-V8 architecture was investigated. The dose-rate-soft-error index parameters of the processor were determined according to the test results, as were the influences on the function and timing parameters of the processor. The power supply balance is affected, which caused the system to reset and be the main source of soft errors. The results showed the circuit recovery time is primarily determined by the internal PLL, while the core power and the output-low-IO ports are more sensitive to the transient dose rate effect. The power-integrity-hardened design is proposed to mitigate the transient radiation effect.     

Spin-lattice relaxation of <Superscript>113</Superscript>Cd and <Superscript>19</Superscript>F nuclear spins in the crystal lattice of CdF<Subscript>2</Subscript> semiconductor crystals with <Emphasis Type="Italic">DX</Emphasis> centers

Temperature dependences of spin-lattice relaxation rates of the ¹¹³Cd and ¹⁹F lattice nuclei in the CdF₂ semiconductor crystals containing bistable In and Ga impurity centers show that the relaxation mechanisms in the CdF₂:In and CdF₂:Ga crystals are different. The basic mechanism of spin-lattice relaxation of the ¹¹³Cd nuclei in the CdF₂:In crystal is the scalar contact’s interaction of nuclear spins with spins of mobile charge carriers of the conduction band. In the CdF₂:Ga crystal, relaxation of the ¹¹³Cd nuclei is controlled by the contact interaction with electrons moving within a narrow band of impurity states. The same mechanism is apparently responsible for relaxation of the ¹⁹F nuclei in this crystal. In the CdF₂:In crystal, the ¹⁹F nuclei relax by the dipole-dipole interaction with electron spins localized at the hydrogen-like orbits of shallow donors.     

Evaluating the effect of temperature on the accuracy of laser simulation of the transient radiation response in semiconductor devices and circuits

The effect is investigated of temperature variation on the accuracy of laser simulation of the transient radiation response (dose-rate effects) in silicon devices and circuits. Temperature-dependent absorption is shown to be the most important factor when the simulation wavelength is 1.06–1.08 μm, the first harmonic of a Nd laser. Computational formulas are derived for equivalent dose rate subject to temperature as part of the investigation. Its results are found to be consistent with experimental data obtained on test structures and some CMOS circuits.     

Transient radiation effects in microwave monolithic integrated circuits based on heterostructure field-effect transistors: Experiment and model

The results of experimental studies and simulations of transient radiation effects in microwave monolithic integrated circuits, based on heterostructure field-effect transistors, affected by the pulse ionizing radiation, are presented. The physical model, which adequately describes transient radiation effects in field-effect transistors in dose rate range up to 10¹² rad/s, is proposed. Based on the physical model, the equivalent electric circuit, taking into account the dominating ionization effects, intended for using in the computer-aided design (CAD), is constructed. The simulated ionizing responses of the microwave low-noise amplifier (LNA) MIC are in accordance with the experimental data.     

Circular polarization of the photoluminescence from a system of two-dimensional <Emphasis Type="Italic">A</Emphasis><Superscript>+</Superscript> centers in a magnetic field

A series of GaAs/AlGaAs quantum well structures with different concentrations of A ⁺ centers is studied experimentally by polarized photoluminescence spectroscopy. The spectral dependences of the circular polarization and the energy shifts in a magnetic field exhibit qualitatively different behavior for samples corresponding to the weak and strong localization conditions. The results obtained are explained in the context of a suggested model describing optical transitions between states of localized and free electrons and A ⁺ centers.     

Evaluating the effect of photogeneration nonuniformity on the accuracy of laser simulation of the transient radiation response in semiconductor devices and circuits

The effect is investigated of photogeneration nonuniformity, both vertical and horizontal, on the accuracy of laser simulation of the transient radiation response (dose-rate effects) in silicon devices and circuits. It is shown that vertical nonuniformity, due to optical absorption by the substrate, has an insignificant effect if the wavelength is selected to be 1.06–1.08 μm, the first harmonic of a Nd laser. Horizontal nonuniformity, due to the metallization pattern, is shown to disappear on a timescale comparable with the laser pulse width for most practical ICs, as a result of lateral flow of excess carriers by diffusion and drift. When this is the case, the influence of the metallization pattern is found to be fully determined by the area of metallization relative to the over-all chip area. Using a diffuser of laser radiation is proposed as a way to reduce this effect. An optical model is developed to calculate equivalent dose for the diffuse radiation. It is demonstrated that this approach indeed alleviates the horizontal nonuniformity of equivalent dose rate related to the metallization pattern. The predictions are verified by experiment.     

Influence of ionizing radiation in electronic and optoelectronic properties of III–V semiconductor compounds

The interaction between radiation and matter is very important in the study of materials used in the aerospace industry. The improvement of the resistance of various devices is crucial. In the present work we have produced simulation results of damages induced in electronic devices of III–V semiconductor compounds, using SRIM-TRIM, CASINO and GEANT4 programs. The energies used for ⁺ particles, SRIM-TRIM, were from 500 keV to 4 MeV for both FETs and HEMTs and the energies used for β⁻ particles, CASINO, were from 1 to 500 keV.     

Effect of microwave treatment on current flow mechanisms in Au-TiB<Subscript>x</Subscript>-Al-Ti-n<Superscript>+</Superscript>-n-n<Superscript>+</Superscript>-GaN-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ohmic contacts

The temperature dependences of the contact resistivity ρ_c of Au-TiB_x Al-Ti-n⁺-n-n⁺-GaN-Al₂O₃ ohmic contacts have been studied before and after microwave treatment followed by nine-nonth room-temperature sample storage. The temperature dependences of ρ_c of initial samples were measured twice. The first measurement showed the temperature dependence typical of ohmic contacts; the repeated measurement in the temperature region above 270 K showed a ρ_c increase caused by metallic conductivity. After microwave treatment, the metallic conductivity in the ohmic contact is not observed. This is presumably associated with local heating of metal Ga inclusions under microwave irradiation and the formation, due to high chemical activity of liquid gallium, of compounds of it with other metallization components. In this case, the temperature dependence of ρ_c is controlled by ordinary charge transport mechanisms. After nine-nonth room-temperature storage, the temperature dependence of ?c is described by the tunneling mechanism of charge transport.     

A high-temperature radiation-resistant rectifier based on p<Superscript>+</Superscript>-n junctions in 4H-SiC ion-implanted with aluminum

A combination of a high-dose (5 s- 10¹⁶ cm^-2) implantation of Al ions into epitaxial n-type 4H SiC layers grown by chemical deposition from th e vapor phase and rapid (15 s) thermal annealing at 1700–1750°C has been used to form layers with a rectangular impurity profile according to the mechanism of solid-phase epitaxial crystallization. The combined effects of enhanced diffusion of radiation defects after implantation and gettering of defects during annealing bring about an improvement in the quality of the initial material, which ensures an increase in the diffusion length of the minority charge carriers by several times. Metastable states annealed within different temperature ranges are formed in SiC under the effect of irradiation with various particles. Low-temperature annealing of radiation defects increases the radiation and temporal lifetime of devices under irradiation. High-temperature annealing of radiation defects makes it possible to vary the lifetime of nonequilibrium charge carriers, i.e, vary the frequency range of devices. The radiation resistance of SiC-based devices increases as the operation temperature is increased to 500°C.     

Effect of H<Superscript>+</Superscript> implantation on the optical properties of semi-insulating GaAs crystals in the IR spectral region

The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interaction of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.     

Effect of Boron Impurity on the Light-Emitting Properties of Dislocation Structures Formed in Silicon by Si<Superscript>+</Superscript> Ion Implantation

The effect of boron implantation on the light-emitting properties of dislocation structures formed in silicon by Si⁺ ion implantation with subsequent annealing is studied. It is shown that the implantation of B⁺ ions has a significant effect on the dislocation-related luminescence intensity, spectrum and the temperature dependence of the D1-band intensity. It is found that the temperature dependence is nonmonotonous and involves two regions, in which the D1-band intensity increases with increasing temperature and has two well-pronounced maxima at 20 K and 60–70 K. The maximum at 20 K is associated with the morphological features of the dislocation structure under study, whereas the maximum at 60–70 K is associated with the additional implantation of the boron impurity into the dislocation region of the samples. It is established that the intensities of the experimentally observed maxima and the position of the high-temperature maximum depend on the implanted boron concentration.     

Study and simulation of electron transport in Ga<Subscript>0.5</Subscript>ln<Subscript>0.5</Subscript>Sb based on Monte Carlo method

This work addresses the issue related to the electronic transport in the III–V ternary material Ga_0.5ln_0.5Sb 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.     

Switching effects in the films based on Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript>

Experimental results on the switching effects related to the phase transitions in Ge₂Sb₂Te₅ in the presence of external voltage or laser irradiation are presented. An electron model of the reversible switching is discussed.