Deep trap spectra and carrier diffusion lengths were measured for unintentionally doped β-Ga2O3 bulk crystals with (100) orientation. The 20-mm diameter, 15-mm length boule was pulled by the Czochralski method from gallium oxide in (010) direction. It is found that the net density of shallow donors in (100) plates cleaved from the crystal was 2.6 × 1017 cm−3, with ionization energies of 0.05 eV measured from admittance spectra. Three deep electron traps with respective ionization energies of 0.6 eV (concentration 1.1 × 1014 cm−3), 0.8 eV (concentration 3.9 × 1016 cm−3) and 1.1 eV (concentration 8.9 × 1015 cm−3) were detected by Deep Level Transient Spectroscopy. The dominant 0.8 eV trap is associated with the E2 centers due to Fe acceptors, the two other traps are the well documented E1 and E3 centers. The major deep acceptors in the lower half of the bandgap have optical ionization threshold of 2.3 eV and concentration of 4 × 1015 cm−3 and are believed to be due to the split Ga vacancies acceptors. The diffusion length of non-equilibrium charge carriers was 90 nm. The electrical properties of these (100) oriented crystals grown by Czochralski are quite similar to those synthesized by the undoped Edge-defined Film-Fed Growth technique.

In this study, α-Ga2O3 films of thickness about 1 μm were epitaxially deposited on m-plane sapphire substrate by halide vapor phase epitaxy. The lattice mismatch between α-Ga2O3 and sapphire substrate is about 3.5 % along c-axis and 4.8 % along a-axis, resulting in the formation of misfit dislocations. High-angle annular dark-field scanning transmission electron microscopy was employed to study the misfit dislocations at the α-Ga2O3/sapphire interface. The study was carried out along the [112‾0] zone axis and focused on the dislocations responsible for a misfit strain relaxation along c-axis. The resulting magnitude of the projected Burgers vector onto (112‾0) plane has been compared with the estimated values for 13<1‾101> and 13<2‾021> dislocations. It has been revealed, that misfit dislocations tend to dissociate into partial dislocations at the interface.

The mechanical strength of silicon wafers of 100 μm thickness was studied. Loading of the wafers was carried out by the "ring-on ring" method, stress and deflection under the small ring were determined by finite element modeling. The validity of the calculation model was checked by comparing the dependences of the deflection under the small ring on the load obtained in the experiment and by the simulation. The effect of methods of wafers obtaining and their surface treatment on the strength, as well as the connection between the strength and surface roughness characteristics were shown. Keywords: silicon, strength, chemical polishing treatment, surface roughness.

Wide bandgap orthorhombic polymorph of gallium oxide (kappa-Ga2O3) possessing a high spontaneous polarization grown on wurtzite-type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such kappa-Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual "suspended" thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR-TEM) including cathodoluminescence (CL-SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron-hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity.

Heterojunctions (HJs) of p-NiO/n-Ga2O3 were prepared by deposition of thin films of p-NiO by ion beam sputtering on bulk nominally undoped (100) oriented n-Ga2O3 samples cleaved from Czochralski-grown (010) oriented crystal. Electrical properties and deep traps spectra were studied and compared with those obtained for similar samples with Ni Schottky diodes. Characteristic features of the NiO/Ga2O3 HJs are the built-in voltage of over 2 V compared to 1 V in Ni Schottky diodes, a strong frequency dispersion of capacitance due to the presence of high density over 10(18) cm(-3) of E-c-0.16 eV traps in the thin region adjacent to the NiO/Ga2O3 interface. For heterojunction diodes the strong increase of reverse current occurs at a much higher voltage than for Schottky diodes (120 V versus 60 V).

The mechanical strength of various silicon wafers with a thickness of 100 μm has been studied, depending on the methods of their preparation and the modes of their subsequent grinding or polishing, including chemical-mechanical (HMP). The plates were loaded using the ring-to-ring method, the magnitude of stresses and deflection under the small ring was determined by the finite element method. For all the samples studied, the profiles and roughness parameters of the plates were obtained by stylus profilometry and atomic force microscopy (AFM) when scanning the surface along the baseline and over the area. A direct correlation was found between the strength of the plates and the characteristic parameters of their surface profile (the average values of the magnitude and period of fluctuations in the height of the irregularities). Keywords: silicon wafer, strength, chemical-mechanical polishing treatment, surface morfology.

Micron-thick layers of (Cr1-xGax)2O3 solid solutions were grown by modified mist chemical vapor deposition (mist-CVD) with three different Ga concentrations. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods were used to analyze the quality of the films. They showed good crystallinity, homogeneity and coalescence of the samples. Solid solution contents estimation was performed via applying Vegard’s law to XRD data and by its results the highest reached Cr:Ga ratio is approximately 1:1. Transmission spectra of solid solutions demonstrated blue-shift of the absorption edge with increase of the Ga contents. Optical bandgap increased from 3.06eV for undoped Cr2O3 sample to 3.73eV for the layer with the highest Ga concentration.

Представлены результаты экспериментального исследования реальной структуры тонких пленок κ-фазы оксида галлия. Методами дифракции обратно отраженных электронов в сканирующем электронном микроскопе и просвечивающей электронной микроскопии установлено, что микро-монокристаллы κ-оксида галлия состоят из совокупности трех типов поворотных доменов орторомбической симметрии, повернутых друг относительно друга на угол 120° вокруг оси роста. Монокристаллические домены характеризуются большой плотностью прямолинейных антифазных границ, формирующих при своем пересечении структуру значительной доли доменных границ.

Thick β-Ga2O3 homoepitaxial films have been grown on (2¯01) commercial substrates by mist-CVD with gallium acetylacetonate precursor for the first time. The growth rate of about 2 μm/h has been reached, which is unavailable for any other known epitaxial technique. The layer is characterized by the constant thickness and reasonable structure quality due to low stressed interface.

Gallium Oxide is a prospective ultra-wide band -gap semiconductor for high -voltage electronics. Bulk beta-Ga2O3 crystals can be utilized as substrates for device structures. The biggest challenge encountered is to grow low defect density wafers with high crystal perfection. In this work a boule with a diameter of about 20 mm and a height of 20 mm was grown by Czochralski method. The separate plates with dimensions of approx. (10 x 5 x 3) mm3 were cleaved out from the crystal along the (100) cleavage planes. XRD investigation demonstrated that the crystal is a monoclinic single -phase structure which is characterized by broad rocking curves. The etch pits density revealed by selective wet etching appeared to be high and was estimated as 2 & sdot; 107 cm - 2. The series of post-growth heat treatments was applied to eliminate these drawbacks. Annealing at 1100 degrees C during 5 h had the most effect on the crystal structure. Namely, its coherent-domain-size value increased over 400 nm, domain misorientation dropped below the arcminute. The crystal developed higher stoichiometry and higher crystalline perfection. Annealing at the same temperature, but for duration of 11 h dramatically worsen all the parameters of the crystal in combination with its fragmentation in smaller-sized domains. The etch pits density finally decreased 40 -fold and took a value of 5 & sdot; 105 cm - 2.

The effect of H 2 , NH 3 , CO and O 2 on the electrically conductive properties of In 2 O 3 films grown by halide vapor phase epitaxy has been studied. In the temperature range of 200-550 o C, In 2 O 3 films demonstrate gas sensitivity to all considered gases, a relatively high operation speed and repeatability of cycles. The greatest response to NH 3 was obtained, which exceeded 33 arb. units at a temperature of 400 o C and a gas concentration of 1000 ppm -1 . A qualitative mechanism of gas sensitivity of In 2 O 3 films is proposed. The obtained gas-sensitive characteristics are compared with known In 2 O 3 sensors based on various materials. It is shown that the method of halide vapor phase epitaxy makes it possible to obtain indium oxide films with high gas sensitivity. Keywords: In 2 O 3 films, halide vapor phase epitaxy, gas-sensitive properties, response.

Record thick (up to 100 μm) epitaxial layers of a prospective metastable semiconductor Ga2O3 were grown by HVPE (Halide Vapor Phase Epitaxy) on GaN buffer layers on c-sapphire substrates. The X-ray diffraction pattern of the layers show that the structure of the layer is a pure κ(ε)-Ga2O3 without any other phases. At the same time, the organization of a domain structure was observed, which manifests itself in the form of pseudohexagonal prisms that retain the orientation of the gallium nitride sublayer. Schottky diodes with nickel contacts were fabricated and the electrical and photoelectric properties of the layers were studied. Capacitance–voltage (C–V) and frequency–capacitance (C–f) dependencies were studied, photocurrent and photocapacitance spectra were measured.

•Gallium Oxide (β-Ga2O3) crystals are utilized as substrates for high-power devices.•Thermal annealing was applied to enhance the perfection of bulk (100) β-Ga2O3 crystals.•Annealing led to increase in coherent-domain-size value and decrease in domain misorientation.•Annealing led to development a higher stoichiometry and higher crystalline perfection.•Annealing decreased etch pits density 40-fold.

Single-crystalline α-Cr 2 O 3 layers were synthesized on a sapphire substrate with a basal orientation in a laboratory reactor using ultrasonic-assisted chemical vapor deposition in the temperature range of 700-850 o C. The influence of the growth temperature on the structural quality of the layer was studied by X-ray diffraction. At a growth temperature of 800 o C, continuous layers with a thickness of about 1 μm were obtained. The layers were transparent in the visible region with a slightly greenish tint and showed some light transmission up to wavelengths of ~ 350 nm. The full width at half maximum of the rocking curve for reflection 0006 was ~ 300 arcsec. Keywords: chromium oxide, CVD epitaxy, wide-bandgap semiconductor.

Thick (3- Ga 2 O 3 homoepitaxial films have been grown on (201) commercial substrates by mist-CVD with gallium acetylacetonate precursor for the first time. The growth rate of about 2 mu m/h has been reached, which is unavailable for any other known epitaxial technique. The layer is characterized by the constant thickness and reasonable structure quality due to low stressed interface.

The results of an experimental study of the real structure of thin films of κ-phase gallium oxide are reported. It has been established by electron backscattering diffraction in a scanning electron microscope and by transmission electron microscopy that gallium oxide single microcrystals consist of three types of rotating domains of the orthorhombic symmetry, which are rotated relative to each other around the growth axis by an angle of 120°. Single-crystal domains are characterized by a high density of straight antiphase boundaries, which, when intersecting, form a significant fraction of the domain wall structure.

In this study, alpha-Ga2O3 films of thickness about 1 mu m were epitaxially deposited on m-plane sapphire substrate by halide vapor phase epitaxy. The lattice mismatch between alpha-Ga2O3 and sapphire substrate is about 3.5 % along c-axis and 4.8 % along a-axis, resulting in the formation of misfit dislocations. High-angle annular dark-field scanning transmission electron microscopy was employed to study the misfit dislocations at the alpha-Ga2O3/sapphire interface. The study was carried out along the [11 (2) over bar0] zone axis and focused on the dislocations responsible for a misfit strain relaxation along c-axis. The resulting magnitude of the projected Burgers vector onto (11 (2) over bar0) plane has been compared with the estimated values for 1/3 < <(1)over bar>101 > and 1/3 < <(2)over bar>021 > dislocations. It has been revealed, that misfit dislocations tend to dissociate into partial dislocations at the interface.

α-Ga2O3/α-Cr2O3 heterostructures with a corundum structure were obtained by chloride vapor phase epitaxy and magnetron sputtering. The structural, electrical conductive and photoelectrical properties of the obtained samples were studied. It was established that the α-Ga2O3/α-Cr2O3 heterostructures exhibits weak rectifying properties and in comparison with α-Ga2O3 films has a higher response speed when exposed to ultraviolet radiation Keywords: Gallium oxide, chromium oxide, corundum, anisotypic heterostructures

The defect structure of α-phase gallium oxide thin films was investigated using transmission electron microscopy (TEM). Epitaxial Ga2O3 films were grown via halide vapor-phase epitaxy on c-plane sapphire substrates. TEM analysis revealed a high density of extended planar defects within the films, primarily located along prismatic planes of {112¯0} type. Displacement vectors were determined using the invisibility criterion for stacking faults. The study encompassed both planar and cross-sectional views of the films. It is hypothesized that these defects form due to the motion of edge partial dislocations with the 13⟨11¯00⟩ Burgers vector. Various mechanisms of their formation have been explored.

The results of a study by transmission electron microscopy of the structural state of α-Ga 2 O 3 film with a thickness of about 1 micron, grown on the prismatic m-face sapphire by the method of chloride vapor phase epitaxy, are presented. The influence of the substrate orientation on the formation of the dislocation structure is discussed. Threading dislocations, including those with the Burgers vector 1/3< 1120 >, and dislocation half-loops are revealed. The inclined propagation of dislocations and the formation of dislocation half-loops result in the reduction of the threading dislocation density near the surface.. Keywords: dislocations, gallium oxide, TEM.