Recent studies have shown that stratigraphically disturbed meteoric ice bedded at Vostok Station between 3318 and 3539 m dates back to 1.2 Ma BP and possibly beyond. As part of the VOICE (Vostok Oldest Ice Challenge) initiative, a new deviation from parent hole 5G-1 was made at depths of 3270–3291 m in the 2018/19 austral season with the aim of obtaining a replicate core of the old ice. Sidetracking was initiated using the standard KEMS-132 electromechanical drill routinely employed for deep ice coring at Vostok, without significant changes to its initial design. Here we describe the method and operating procedures for replicate coring at a targeted depth in an existing slant hole, involving the use of a cable-suspended electromechanical drill. The design of the milling cutter head used for sidetracking is presented. The performance characteristics and the experience of drilling branch-hole 5G-5 at Vostok are described and discussed.

The VF3-type compound GaF3 has been studied by high-pressure angle-dispersive X-ray diffraction in the pressure range from 0.0001 to 10 GPa. The compression mechanism was found to be highly anisotropic. The c-axis shows little pressure dependence (≈0.4%), but exhibits negative linear compressibility up to ≈3 GPa where it achieves its maximum length. In contrast, the length of the a-axis is reduced by ≈8.8% at the highest measured pressure and an anomalous reduction in the linear compressibility is observed at 4 GPa. The zero pressure bulk modulus B0 was determined to B0 = 28(1) GPa. The compression mechanism of GaF3 is discussed in terms of deformation of an 8/3/c2 sphere-packing model. The volume reduction of GaF3 is mainly achieved through coupled rotations of the GaF6 octahedra within the entire measured pressure range, which reduces the volume of the cubooctahedral voids. In addition, the volume of the GaF6 octahedra also decreases for p ≲ 4.0 GPa, but remains constant above this pressure. The volume reduction of the GaF6 octahedra is accompanied by an increasing octahedral strain. Isosurfaces of the procrystal electron density are used for visualization of the cubooctahedral voids at different pressures.

Thick low defect AlN and AlGaN layers grown on ultra violet (UV) transparent substrates are considered as promising substrate materials for the UV light emitters and detectors. Electrically insulating thick AlN layers may serve as the substrates for AlGaN/GaN-based high power high electron mobility transistors (HEMTs). In this paper we report on crack-free up to 20 μm thick AlN layers grown by stress control HVPE on 2-inch sapphire substrates. As-grown surface had a characteristic pyramidal morphology. Being thick enough, AlN layers can be polished to improve surface roughness. The minimum full width at half maximum (FWHM) values of AlN ω-scan x-ray (00.2) and (10.2) rocking curves was about 500 and 1000 arcsec, respectively. The XRD analysis was applied for the threading dislocation density evaluation in grown AlN layer. Screw dislocation density was found to be (3-7)×108 cm-2 for the layers from 3 to 12 μm thick.

This paper contains results on InN growth by Hydride Vapor Phase Epitaxy (HVPE) on various substrates including sapphire, GaN/sapphire, AlGaN/sapphire, and AlN/sapphire templates. The growth processes were carried out at atmospheric pressure in a hot wall reactor in the temperature range from 500 to 650°C. Arrays of nano-crystalline InN rods with various shapes were grown directly on sapphire substrates. Continuous InN layers were grown on GaN/sapphire, AlN/sapphire and AlGaN/sapphire template substrates. X-ray diffraction rocking curves for the (00.2) InN reflection exhibit the full width at half maximum (FWHM) as narrow as 0.075 deg. for the nano-rods and 0.128 deg. for the continuous layers grown on GaN/sapphire templates.

This paper presents result of investigation of the oxygen interaction with a surface of semiconductor metal oxide film. The idea to carry out such research is connected with the key role, which oxygen plays in the processes of impurity gas molecules detection in atmosphere and semiconductor surface sensibilization. Numerical modeling of the interaction was carried out for different temperatures and oxygen partial pressures. Results of modeling are compared with the results of experimental study of oxygen-semiconductor film system.

Results of investigation aimed at the improvement of gas sensitive characteristics of tin dioxide thin film's based gas sensors through their treatment in high frequent (HF) oxygen plasma and sensibilization by means of doping are presented.

Tin dioxide thin films were deposited from alcohol solutions of SnCl45H2O by means of chemical spray pyrolysis method on alumina substrate at the temperatures in the range from 400 to 500°C. The thickness of films was varied in the range 20–100 nm.

Surface treatment of obtained tin dioxide layers was carried out in pure oxygen plasma at room temperature and 3-4 times increase of the resistance and gas sensitivity was obtained at that. These parameters' changing is discussed from the point of view of thin film's stoichiometry alteration, for control of which there were used IR and SIMS measurements. Obtained results are compared with results of the film's high temperature (∼600oC) thermal annealing on air.

To increase thin film's gas sensitivity and selectivity the doping with Pd and Cu was applied. Doping was carried out also through chemical spray pyrolysis method from the solutions of corresponding compounds of Pd and Cu. Such modification of SnO2 surface hasallowed to increasing sensitivity to H2 up to 5.103 rel. units (high selectivity) at the simultaneous shift of sensitivity maximum from 350 to 150°C. Doping with Cu has allowed to increasing 4-5 times sensitivity and selectivity toward CH4 and C3H8 gases in air and reducing operating temperatures from 500–520°C to 350–370°C.

It is concluded that combination of HF oxygen plasma tin dioxide film' treatment and its surface sensibilization is an effective way to considerably improvement of gas sensitive and selective characteristics of tin dioxide based thin film gas sensors (TFGS).

Waveguide prism-coupling methods were used to measure the ordinary and extraordinary refractive indices of AlxGa1-xN films grown on sapphire substrates by HVPE and MOCVD. Several discrete wavelengths ranging from 442 nm to 1064 nm were used and the results were fit to one-term Sellmeier equations. The maximum standard uncertainty in the refractive index measurements was ± 0.005 and the maximum standard uncertainty in the self-consistent calculation for film thickness was ± 15 nm. Analysis of normal-incidence spectroscopic transmittance and reflectance measurements, correlated with the prism-coupling results, was used to determine the ordinary refractive index as a continuous function of wavelength from the band gap wavelength of each sample (between 252 nm and 364 nm) to 2500 nm. The Al compositions of the samples were determined using energy-dispersive X-ray spectroscopy analysis (EDS). HVPE grown samples had compositions x = 0.279, 0.363, 0.593, and 0.657. MOCVD samples had x = 0.00, 0.419, 0.507, 0.618, 0.660, and 0.666. The maximum standard uncertainty in the absolute EDS-determined value for x was ± 0.02.

The hardness of single-crystal aluminum nitride (AlN) 0.5-mm-thick wafers was measured at elevated temperatures and compared with that of other semiconductors. A Vickers indentation method was used to determine the hardness under an applied load of 0.5 – 5 N in the temperature range 20 - 1400°C. The average hardness was measured as 17.7 GPa at room temperature, harder than GaN and InN. The fracture toughness is 0.5 MPa•m1/2. AlN exhibits the hardness higher than that of GaN in the entire temperature range investigated. Up to about 1100°C, AlN maintains its hardness and thus, a high mechanical stability for AlN at elevated temperatures is deduced.

We describe the growth of high quality AlN and GaN on Si(111) by gas source molecular beam epitaxy (GSMBE) with ammonia (NH3). The initial nucleation (at 1130−1190K) of an AlN monolayer with full substrate coverage resulted in a very rapid transition to two-dimensional (2D) growth mode of AlN. The rapid transition to the 2D growth mode of AlN is essential for the subsequent growth of high quality GaN, and complete elimination of cracking in thick ( > 2 μm) GaN layers. We show, using Raman scattering (RS) and photoluminescence (PL) measurements, that the tensile stress in the GaN is due to thermal expansion mismatch, is below the ultimate strength of breaking of GaN, and produces a sizable shift in the bandgap. We show that the GSMBE AlN and GaN layers grown on Si can be used as a substrate for subsequent deposition of thick AlN and GaN layers by hydride vapor phase epitaxy (HVPE).

We report on AlN wafers fabricated by hydride vapor phase epitaxy (HVPE). AlN thick layers were grown on Si substrates by HVPE. Growth rate was up to 60 microns per hour. After the growth of AlN layers, initial substrates were removed resulting in free-standing AlN wafers. The maximum thickness of AlN layer was about 1 mm. AlN free-standing single crystal wafers with a thickness ranging from 0.05 to 0.8 mm were studied by x-ray diffraction, transmission electron microscopy, optical absorption, and cathodoluminescence.

Deep levels studies on a set of n-GaN films grown by MOCVD and HVPE reveal the presence of electron traps with levels near Ec−0.25 eV, Ec−0.55 eV, Ec−0.8 eV, Ec−1 eV, hole traps with levels near Ev+0.9 eV and a band of relatively shallow states in the lower half of the bandgap. The total density of these latter states was estimated to be some 1016 cm−3 and they were tentatively associated with dislocations in GaN based on their high concentration and band-like character. None of the electron or hole traps could be unambiguously related with strong changes of diffusion lengths of minority carriers in various samples. It is proposed that such changes occur due to different surface recombination velocities. An important role of Ec−0.55 eV traps in persistent photoconductivity phenomena in n-GaN has been demonstrated.

Deep levels studies on a set of n-GaN films grown by MOCVD and HVPE reveal the presence of electron traps with levels near Ec-0.25 eV, Ec-0.55 eV, Ec-0.8 eV, Ec-1 eV, hole traps with levels near Ev+0.9 eV and a band of relatively shallow states in the lower half of the bandgap. The total density of these latter states was estimated to be some 1016 cm−3 and they were tentatively associated with dislocations in GaN based on their high concentration and band-like character. None of the electron or hole traps could be unambiguously related with strong changes of diffusion lengths of minority carriers in various samples. It is proposed that such changes occur due to different surface recombination velocities. An important role of Ec-0.55 eV traps in persistent photoconductivity phenomena in n-GaN has been demonstrated.

We describe the growth of high quality AlN and GaN on Si(111) by gas source molecular beam epitaxy (GSMBE) with ammonia (NH3). The initial nucleation (at 1130-1190K) of an AlN monolayer with full substrate coverage resulted in a very rapid transition to two-dimensional (2D) growth mode of AlN. The rapid transition to the 2D growth mode of AlN is essential for the subsequent growth of high quality GaN, and complete elimination of cracking in thick ( > 2 μm) GaN layers. We show, using Raman scattering (RS) and photoluminescence (PL) measurements, that the tensile stress in the GaN is due to thermal expansion mismatch, is below the ultimate strength of breaking of GaN, and produces a sizable shift in the bandgap. We show that the GSMBE AlN and GaN layers grown on Si can be used as a substrate for subsequent deposition of thick AlN and GaN layers by hydride vapor phase epitaxy (HVPE).

We report on AlN wafers fabricated by hydride vapor phase epitaxy (HVPE). AlN thick layers were grown on Si substrates by HVPE. Growth rate was up to 60 microns per hour. After the growth of AlN layers, initial substrates were removed resulting in free-standing AlN wafers. The maximum thickness of AlN layer was about 1 mm. AlN free-standing single crystal wafers with a thickness ranging from 0.05 to 0.8 mm were studied by x-ray diffraction, transmission electron microscopy, optical absorption, and cathodoluminescence.

The paper suggests a criterion for selection of radiation stable semiconductors and dielectrics.

The search for materials with great radiation stability (RS) is one of the basic problems in materials science. The absolute RS of crystals could be provided only in case when all elementary radiation defects (Frenkel pairs) are unstable, and annihilated immediately at any low temperatures in the places whete they were born. The presence of an instability zone (IZ) of point defects vacancy (v) - interstitial atom (i) is a necessary condition for RS [1,2]. The characteristic radius r0 of IZ at v-i Coulomb interaction is on the order of 10-30 Å [3]. The important parameter is a mean distance x between stopping point of atom i, knocked out from its site, and the v born at this site. Without taking into account the periodic structure, the analytical expression for x was obtained[4]. The value of x appears to be not large. For example, if the knocked out atom has the energy of 10 keV, the mean distance between v and i is 10 Å in iron, and only 3 Å in copper (x < r0). So, the greatest part of i's seem to remain in IZ, and therefore must recombine with “their” own v's. This would result in RS being greater than what was really observed in majority of nonmetal crystals.