Sh. A. Yusupova

Current-voltage characteristics of Si/Si1 − xGex heterodiodes fabricated by direct bonding

We have studied the current-voltage (I–U) characteristics of Si/Si1 − xGex (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si1 − xGex wafers of the same orientation containing 2–15 at % Ge. An increase in the germanium concentration NGe in Si1 − xGex crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I–U curve. However, for all samples with NGe ≤ 15 at %, the I–U curves of Si/Si1 − xGex heterodiodes are satisfactory in the entire range of current densities (1 mA/cm2–200 A/cm2). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si1 − xGex heterostructures.

Structural and electrical properties of SiGe-on-insulator substrates fabricated by direct bonding

A new method for fabricating SiGe-on-insulator substrates, i.e., direct bonding of thermally oxidized Si wafers with Si1 − xGex wafers cut from Czochralski-grown crystals, is suggested. Si1 − xGex layers no larger than 10 μm thick in SiGe/SiO2/Si compositions were fabricated by chemical mechanical polishing. To increase the Ge content in the Si1 − xGex layer, thermal oxidation was used. It was shown that the increase in the Ge content and heat treatment procedures at 1250°C are not accompanied by degradation of structural and electrical characteristics of Si1 − xGex layers.

High-power subnanosecond silicon avalanche shaper

The ultrafast (subnanosecond) switching of a high-voltage silicon avalanche shaper (SAS) diode from a blocking to conducting state is performed by applying an overvoltage pulse with a wavefront rise-rate of ~1012 V/s in the reverse direction. The forming under this condition impact ionization front fills in the diode base layer with electron-hole plasma and switches the diode to the conducting state. Besides, it is important to prevent the possible breakdown over the diode structure surface while the overvoltage pulse is applied. The first results of the investigation of principally new SAS diode design is presented. New diode construction completely excludes edge contour degradation by the overvoltage pulse. Our experiments show the usefulness of the suggested diode construction and the importance of further investigations to determine its operation limits.

The formation of shallow-donor distribution profiles in proton irradiation of silicon

A study of the formation of shallow hydrogen-containing donors (hydrogen-related shallow thermal donors, STD(H)) in silicon under proton irradiation followed by annealing in a temperature range of 300–500°C is reported. The effect of postimplantation annealing regimes on the concentration distribution of shallow donors at various proton energies and fluences is examined. It is shown that the shape of the concentration profiles strongly varies with temperature and annealing duration when a fixed concentration of radiation defects is introduced and equally with energy and dose at a given annealing temperature. It is also shown that the process in which hydrogen-containing shallow donors are formed is accompanied by the appearance in n-type silicon of H-induced buried n′-layers, the formation of which near the pn junction in the high-resistivity n-base of diode structures allows the breakdown voltage of high-voltage pn junctions to be controlled. In the general case, this makes it possible to improve the characteristics of power silicon devices of various purposes.

Bulk GaN layers grown on oxidized silicon by vapor-phase epitaxy in a hydride-chloride system

Bulk GaN layers with a thickness of up to 1.5 mm and a lateral size of 50 mm were grown by hydride-chloride vapor-phase epitaxy (HVPE). The best samples show a half-width (FWHM) of the X-ray rocking curve of ωθ=27′, a charge carrier density of ∼8 × 1019 cm−3, and a mobility of ∼50 cm2/(V s). The photoluminescence spectra of the obtained epitaxial GaN layers exhibit an edge emission band at 348 eV. The HVPE layers are characterized by a high mechanical strength: HV = 14 GPa.

Correlation between the electrical and luminescent properties of high-purity gallium arsenide

Epitaxial n-GaAs layers with a background impurity concentration of ND-NA<1015 cm−3, grown by chloride vapor phase epitaxy in an open system, exhibit correlation between the electrical properties and the long persistence of the edge photoluminescence lines D0x and D0h related to the hole trapping centers. An increase in the concentration of such trapping centers in n-GaAs leads to a decrease in the mobility of free charge carriers.

Impurity centers of rare-earth ions (Eu, Sm, Er) in GaN wurtzite crystals

Gallium nitride (GaN) was doped with Eu, Sm, and Er impurities using the diffusion method. The behavior of rare-earth impurities (the formation of donor or acceptor levels in the GaN band gap) correlates with the total concentration of defects, which is determined from optical measurements, and with the position of the Fermi level in starting and doped crystals. The intensity of emission lines, which are characteristic of the intracenter f-f transition of rare-earth ions, is controlled by the total defect concentration in the starting semiconductor matrix.

Bulk large-area GaN layers

Mirror-smooth, transparent bulk GaN layers with an area of 2×3 cm2 and a thickness of up to 1 mm were grown by hydrochloride vapor-phase epitaxy. Cracking of the material was eliminated by using a two-stage growth process; separation from a substrate was provided by a low-temperature buffer layer of preset thickness. For the best samples, FWHM of the X-ray rocking curve was ωθ=3.5′ and the dislocation density amounted to 107–108 cm−2.

The absorption spectra of gallium nitride crystals doped with erbium ions

We have measured the absorption spectra of Er3+ ions introduced by diffusion into bulk GaN crystals grown by vapor phase epitaxy in a chloride system. The wavelength interval of 518–527 nm corresponding to the region of the 4I15/2→2H11/2 transition was studied in detail at 293, 77, and 2 K. At 2 K, the spectrum of this transition displays six lines, which correspond to the theoretically possible number of sublevels of the 2H11/2 state of Er3+ ion occurring in a noncubic crystal field. The positions of levels in the 2H11/2 multiplet correspond to 2.360, 2.361, 2.365, 2.369, 2.379, and 2.386 eV. Both the number and narrow width of lines observed at 2 K indicate that Er3+ ions predominantly occupy the same regular position in GaN crystals. Most probably, erbium ions occupy gallium sites in the crystal lattice.

Influence of Au and Pt on the concentration profile of Mn in Si

The influence of diffusion of gold and platinum from the layer deposited on the silicon surface on the concentration profile of 54Mn in the bulk is investigated using the radiochemical technique. The data obtained indicate that the manganese concentration in the bulk of silicon is reduced due to annealing of the samples Si〈54Mn〉 with the gold or platinum layer on the surface.