Raman scattering in InP doped by Be<Superscript>+</Superscript>-ion implantation

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.     

Formation of Precipitates in Si Implanted with <Superscript>64</Superscript>Zn<Superscript>+</Superscript> and <Superscript>16</Superscript>O<Superscript>+</Superscript> Ions

The results of studying the surface Si layer and precipitate formation in CZ n-Si(100) samples sequentially implanted with ⁶⁴Zn⁺ ions with a dose of 5 × 10¹⁶ cm² and energy of 100 keV and ¹⁶O⁺ ions with the same dose but an energy of 33 keV at room temperature so that their projection paths R_p = 70 nm would coincide are presented. The post-implantation samples are annealed for 1 h in an inert Ar medium in the temperature range of 400–900°C with a step of 100°C. The profiles of the implanted impurities are studied by time-of-flight secondary ion mass spectrometry. The Si surface is visualized using a scanning electron microscope, while the near-surface layer is visualized with the help of maps of elements formed by Auger electron spectroscopy with profiling over depth. The ZnO(002) texture is formed in an amorphized Si layer after the implantation of Zn and O ions. ZnO(102) crystallites of 5 nm in size are found in a recrystallized single-crystalline Si layer after annealing in Ar at 700°C.     

Reverse Breakdown Voltage Measurement for Power P<Superscript>+</Superscript>NN<Superscript>+</Superscript> Rectifier

The measurement of the reverse breakdown voltage for power rectifier is an important test. Two test methods for the reverse breakdown voltage measurement are employed in the industry, namely the forced voltage test (FVT) and the forced current test (FCT). In this work, we perform a systematic study to explain the different breakdown voltages obtained from the two test methods and the possible damage mechanisms to the device under test during FVT and FCT. The study shows that FVT has a much shorter test time while FCT is less destructive to the device under test.

Electrical properties of Zinc-Tin diarsenide (ZnSnAs<Subscript>2</Subscript>) irradiated with H<Superscript>+</Superscript> ions

The results of studying the electrical properties and isochronous annealing of p-ZnSnAs₂ irradiated with H⁺ ions (energy E = 5 MeV, dose D = 2 × 10¹⁶ cm^?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R _H (D)_lim ≈ ?4 × 10³ cm³ C^?1, conductivity σ (D)_lim ≈ 2.9 × 10^?2 Ω^?1 cm^?1, and the Fermi level position F _lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs₂ compound is calculated.     

Low-temperature relaxation of elastic stresses in SiGe/Si heterostructures irradiated with Ge<Superscript>+</Superscript> ions

Pseudomorphic Si_0.76Ge_0.24/Si heterostructures grown by molecular-beam epitaxy were irradiated with 350-keV Ge⁺ ions at a temperature of 400°C so that the peak of the ions’ energy losses was located within the silicon substrate (deeper than the SiGe-Si interface). The effect of ion implantation on the relaxation of elastic stresses and the defect structure formed as a result of postimplantation annealing is studied. It is found that annealing at a temperature even as low as 600°C makes it possible to ensure a very high degree of relaxation of elastic stresses in the heterostructure and a comparatively low density of threading dislocations in the SiGe layer (<10⁵ cm^?2). The results obtained make it possible to suggest a method for the formation of thin SiGe/Si layers that feature a high degree of relaxation, low density of threading dislocations, and a good surface morphology.     

Electrical properties of isotype <Emphasis Type="Italic">N</Emphasis><Superscript>+</Superscript>-GaSb/n<Superscript>0</Superscript>-GaInAsSb/<Emphasis Type="Italic">N</Emphasis><Superscript>+</Superscript>-GaAlAsSb type-II heterojunctions

Band diagrams and current-voltage and capacitance-voltage characteristics of isotype N ⁺-GaSb/n⁰-GaInAsSb/N ⁺-GaAlAsSb heterostructures have been studied. Dark-current flow mechanisms have been analyzed. It is shown that a staggered type-II heterojunction can behave as a Schottky diode and its current-voltage characteristics exhibit rectifying properties over the entire temperature range 90–300 K. The thermionic-emission current predominates at high temperatures and low voltages. This current is due to thermal excitation of electrons from GaInAsSb to GaSb over the barrier at the heterointerface. A comparison of the relevant theoretical and experimental data confirmed that the tunneling charge transport mechanism plays the key role at low temperatures under both forward and reverse biases.     

Accumulation of structural defects in silicon irradiated with PF<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>+</Superscript></Stack> cluster ions with medium energies

The method of Rutherford backscattering spectrometry in combination with channeling is used to study the accumulation of structural defects in silicon at room temperature as a result of irradiation with P⁺ and F⁺ atomic ions and also with cluster PF _n ⁺ ions (n = 1, …, 4) with the energy of 2.1 keV/amu and with identical generation rate of primary defects. The conditions for correct comparison of the results of bombardment with atomic and cluster ions composed of atoms of various types are suggested. It is found that the characteristics of accumulation of structural defects in silicon in the case of bombardment with PF _n ⁺ cluster ions differ widely from those under irradiation with both atomic ions that are involved in the cluster ion (P⁺ and F⁺) and with atomic heavy ions that have atomic mass close to that of the mass of a PF _n ⁺ cluster. It is shown that, with irradiation conditions being the same, cluster ions produce much more radiation defects in the surface region than do atomic ions; i.e., a molecular effect is observed. Plausible mechanisms of this phenomenon are considered.     

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.     

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.     

Properties of Ge nanocrystals formed by implantation of Ge<Superscript>+</Superscript> ions into SiO<Subscript>2</Subscript> films with subsequent annealing under hydrostatic pressure

The influence of hydrostatic compression on the implantation-induced synthesis of Ge nanocrystals in SiO₂ host was studied. It is found that high-temperature annealing under pressure leads to retardation of Ge diffusion in SiO₂. It is shown that unstressed Ge nanocrystals are formed as a result of conventional annealing (under atmospheric pressure). Annealing under pressure is accompanied by formation of hydrostatically stressed Ge nanocrystals. The stress in Ge nanocrystals was determined from optical-phonon frequencies in the Raman spectra. The shift of Raman resonance energy (E₁, E₁ + Δ₁) corresponds to the quantization of the ground-state energy for a two-dimensional exciton at the critical point M₁ of germanium. It is ascertained that a photoluminescence band peaked at 520 nm is observed only in the spectra of the films which contain stressed Ge nanocrystals.     

Cathodoluminescence properties of yttrium aluminum garnet doped with Eu<Superscript>2+</Superscript> and Eu<Superscript>3+</Superscript> ions

Yttrium aluminium garnet (YAG) doped with Eu²⁺ and Eu³⁺ ions is very interesting as a phosphor for conversion of light-emitting diode light for white light sources. The europium ion occupies the structural position of yttrium in yttrium aluminium garnet and has valence state Eu³⁺. Our sample was doped with Zr⁴⁺, which is why some of the europium ions had valence state Eu²⁺. As a rule, luminescence of Eu³⁺ ions is observed in the orange and red range of spectrum. The luminescence of Eu²⁺ in yttrium aluminum garnet is characterized by an intensive broad band with maximum of intensity at about 560 nm (green color). In this work, we studied the intensity and decay time dependences on europium concentration, and the influence of excitation power density on the cathodoluminescence of the sample. The most interesting result is the change of visible cathodoluminescence color in dependence on the density of the exciting power. The text was submitted by the authors in English.     

Si/SiGe PMOSFET USING P^＋ IMPLANTATION TECHNOLOGY

Si/SiGe P-channel Metal-Oxide-Semiconductor Field Effect Transistor （PMOSFET） using P^＋ （phosphor ion） implantation technology is successfully fabricated. P^＋ implantation into SiGe virtual substrate induces a narrow defect region slightly below the SiGe/Si interface, which gives rise to strongly enhanced strain relaxation of SiGe virtual substrate. X-Ray Diffraction （XRD） tests show that the degree of relaxation of SiGe layer is 96% while 85% before implantation. After annealed, the sample appeared free of Threading Dislocation densities （TDs） within the SiGe layer to the limit of Transmission Electron Microscopy （TEM） analysis. Atomic Force Microscope （AFM） test of strained Si channel surface shows that Root Mean Square （RMS） is 1.1nm. The Direct Current （DC） characters measured by HP 4155B indicate that the maximum saturated transconductance is twice bigger than that of bulk Si PMOSFET.     

The X<Superscript>+</Superscript> trion in a system with spatial separation of the charge carriers

A system composed of two heavy holes located in a two-dimensional (2D) quantum well (QW) and bound via mediation of an electron in a neighboring 2D QW is considered. Using a simple qualitative trial wave function, the ground-state energy of this kind of X⁺ trion is determined in the infinite-hole-mass approximation as a function of the QW spacing. Coordinate dependence of the effective potential binding the holes to each other is calculated for different values of QW spacing. In the adiabatic approximation, a set of dependences describing the X⁺ trion binding energy as a function of the electron mass to the hole mass ratio is obtained. Several estimates for the trion binding energy in GaAs-and ZnSe-based double-QW heterostructures are given.     

Excitation of Er<Superscript>3+</Superscript> ions in SiO<Subscript>2</Subscript> with Si nanocrystals

Probabilities of excitation of erbium ions via Coulomb interaction with carriers localized in silicon nanocrystals embedded in SiO₂, in recombination and intraband relaxation of these carriers, have been calculated.     

Lateral schottky GaN rectifiers formed by Si<Superscript>+</Superscript> ion implantation

Type conversion of p-GaN by direct Si⁺ ion implantation and subsequent annealing was demonstrated by the fabrication of lateral Schottky diodes. The Si⁺ activation percentage was measured as a function of annealing time (30–300 sec) and temperature (1,000–1,200°C), reaching a maximum of ∼30% for 1,200°C, 2-min anneals. The resulting n-type carrier concentration was 1.1×10¹⁸ cm⁻³ for a moderate Si⁺ ion dose of ∼2×10¹⁴ cm⁻². The lateral Schottky diodes displayed a negative temperature coefficient of −0.15 V·K for reverse breakdown voltage.     

Radiative recombination in Ge<Superscript>+</Superscript>-implanted SiO<Subscript>2</Subscript> films annealed under hydrostatic pressure

Photoluminescence (PL) spectra and PL excitation spectra were recorded at room temperature from SiO₂ films implanted with Ge⁺ ions and annealed at temperature T _a =450–1100°C under hydrostatic pressure P=12 kbar. The emergence of features in the violet and green bands of the PL and PL excitation spectra correlates with the formation of hydrostatically strained Ge nanocrystals. The shift of the PL bands to higher energies, which occurs as the annealing temperature is raised to T _a ≥800°C, can be attributed to a shift of the energy levels related to the radiative recombination centers, which is caused by the increasing deformation potential. The observed PL is accounted for by the enhanced probability of direct radiative transitions in Ge nanocrystals with an X-like conduction band.     

Analysis of the dipole matrix elements of electronic optical transitions in the P<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>/Si system

This study is concerned with a singly ionized pair of phosphorus donors in the silicon crystal lattice. The results of numerical calculations of the energy spectrum and dipole matrix elements in such a system are reported. The conditions, in which the P₂⁺/Si system can be used in the implementation of quantum operations with resonance laser pulses, are determined. Estimation of the time of such operations yields ∼10 ps.     

Advantages of the use of supertip Xe<Superscript>+</Superscript> sources with field gas ionization in ion microscopes

Advantages of the use of beams of focused Xe⁺ ions obtained from supertip sources with field ionization (GFIS*) in ion microscopy compared with conventional sources of different ions are considered. Specifically, the higher working temperature of supertip Xe⁺ sources with field gas ionization as well as the higher values of the interaction sections of the Xe⁺ ions with different solid targets are a considerable technical advantage. The properties of focused Xe⁺ ion beams with a special accent on optimization of ion-optical systems of microscopes are evaluated. The possibilities of nanomodification and elemental analysis of materials with the use of beams of Xe⁺ ions are considered.     

Magnetic Patterning of Co/Pt Multilayers by Ga<Superscript>+</Superscript> Ion Irradiation

Patterns separated by approximately 55-nm-wide lines on Co/Pt multilayers have been fabricated using a focused ion beam with a 30-keV Ga⁺ ion source. The ion irradiation allows the magnetic moment in the irradiated lines to rotate 45 deg to 90 deg toward the film plane. The in-plane magnetization component of the irradiated lines increases as the ion dose increases. The balance of incoming and outgoing flux at intersections is maintained in orthogonal patterns, while exceptions have been observed in hexagonal and triangular patterns. In all patterns, irradiated lines and adjacent unirradiated elements have no magnetic interaction.     

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.