High-speed solar-blind short wavelength ultraviolet radiation detectors based on kappa(epsilon)-Ga2O3 layers with Pt contacts were demonstrated and their properties were studied in detail. The kappa(epsilon)-Ga2O3 layers were deposited by the halide vapor phase epitaxy on patterned GaN templates with sapphire substrates. The spectral dependencies of the photoelectric properties of structures were analyzed in the wavelength interval 200-370 nm. The maximum photo to dark current ratio, responsivity, detectivity and external quantum efficiency of structures were determined as: 180.86 arb. un., 3.57 A/W, 1.78 x 10(12) Hz(0.5)center dot cm center dot W-1 and 2193.6%, respectively, at a wavelength of 200 nm and an applied voltage of 1 V. The enhancement of the photoresponse was caused by the decrease in the Schottky barrier at the Pt/kappa(epsilon)-Ga2O3 interface under ultraviolet exposure. The detectors demonstrated could functionalize in self-powered mode due to built-in electric field at the Pt/kappa(epsilon)-Ga2O3 interface. The responsivity and external quantum efficiency of the structures at a wavelength of 254 nm and zero applied voltage were 0.9 mA/W and 0.46%, respectively. The rise and decay times in self-powered mode did not exceed 100 ms.

As areas of application of terahertz (THz) radiation expand in science and practice, evidence is accumulating that this type of radiation can affect not only biological molecules directly but also cellular processes as a whole. In this study, the transcriptome in cells of the thermophilic bacterium Geobacillus icigianus was analyzed immediately after THz irradiation and at 10 min after its completion. THz irradiation does not affect the activity of heat shock protein genes and diminishes the activity of genes whose products involved in peptidoglycan recycling, participate in redox reactions and in protection of DNA and proteins from damage. Gene systems responsible for the homeostasis of transition metals (copper, iron, and zinc) proved to be the most sensitive to THz irradiation; downregulation of these systems increased significantly 10 min after the end of the irradiation. It was also hypothesized that some negative effects of THz radiation on metabolism in G. icigianus cells are related to disturbances in activities of gene systems controlled by metal-sensitive transcription factors.

The photoelectric and structural properties of In2O3-Ga2O3 composite films deposited by halide vapor phase epitaxy on sapphire substrates were investigated. The deposited films were a composite of cubic c-In2O3 and delta-Ga2O3 phases with a low content (InxGa1-x)(2)O-2.4 solid solution deficient in oxygen phase at the surface region. The spectral dependencies of the responsivity, external quantum efficiency, and detectivity were studied in the wavelength interval from 205 to 360 nm. The In2O3-Ga2O3 composite films demonstrated high photosensitivity, low base resistance, and wide spectral interval of sensitivity, including UV-C, UV-B, and UV-A wavelength ranges. The maximum external quantum efficiency and responsivity of the In2O3-Ga2O3 composite films achieved under radiation exposure at a wavelength of 214 nm and electric field strength of 1 kV/cm were 3.8 x 105% and 660 A/W, respectively. A mechanism for the high photosensitivity of the In2O3-Ga2O3 composite films based on the bipolar generation of charge carriers mainly in the segregated regions of the delta-Ga2O3 phase is proposed.

Detectors were developed for detecting irradiation in the short-wavelength ultraviolet (UVC) interval using high-quality single-crystalline alpha-Ga2O3 films with Pt interdigital contacts. The films of alpha-Ga2O3 were grown on planar sapphire substrates with c-plane orientation using halide vapor phase epitaxy. The spectral dependencies of the photo to dark current ratio, responsivity, external quantum efficiency and detectivity of the structures were investigated in the wavelength interval of 200-370 nm. The maximum of photo to dark current ratio, responsivity, external quantum efficiency, and detectivity of the structures were 1.16 x 10(4) arb. un., 30.6 A/W, 1.65 x 10(4)%, and 6.95 x 10(15) Hz(0.5)cm/W at a wavelength of 230 nm and an applied voltage of 1 V. The high values of photoelectric properties were due to the internal enhancement of the photoresponse associated with strong hole trapping. The alpha-Ga2O3 film-based UVC detectors can function in self-powered operation mode due to the built-in electric field at the Pt/alpha-Ga2O3 interfaces. At a wavelength of 254 nm and zero applied voltage, the structures exhibit a responsivity of 0.13 mA/W and an external quantum efficiency of 6.2 x 10(-2)%. The UVC detectors based on the alpha-Ga2O3 films demonstrate high-speed performance with a rise time of 18 ms in self-powered mode.

As areas of application of terahertz (THz) radiation expand in science and practice, evidence is accumulating that this type of radiation can affect not only biological molecules directly, but also cellular processes as a whole. In this study, the transcriptome in cells of the thermophilic bacterium Geobacillus icigianus was analyzed immediately after THz irradiation (0.23 W/cm2, 130 μm, 15 min) and at 10 min after its completion. THz irradiation does not affect the activity of heat shock protein genes and diminishes the activity of genes whose products are involved in peptidoglycan recycling, participate in redox reactions, and protect DNA and proteins from damage, including genes of chaperone protein ClpB and of DNA repair protein RadA, as well as genes of catalase and kinase McsB. Gene systems responsible for the homeostasis of transition metals (copper, iron, and zinc) proved to be the most sensitive to THz irradiation; downregulation of these systems increased significantly 10 min after the end of the irradiation. It was also hypothesized that some negative effects of THz radiation on metabolism in G. icigianus cells are related to disturbances in activities of gene systems controlled by metal-sensitive transcription factors.

The MSM structures based on high-quality 1.6- $\mu \text{m}$ -thick $\alpha $ -gallium oxide (Ga2O3) films grown by the halide vapor phase epitaxy with Ti/Ni interdigital contacts were developed for the detection of short-wave ultraviolet (UVC) radiation. The spectral dependences of responsivity, external quantum efficiency (EQE), and detectivity of MSM structures based on $\alpha $ -Ga2O3 were studied in the wavelength range of 205–260 nm. The responsivity, the EQE, and the detectivity are $7.19\times104$ A $\times \,\,\text{W}^{-{1}}$ , $3.79\times105$ arb.un., and $1.12\times1018$ Hz $^{\text {0.{5}}} \times $ cm $\times \,\,\text{W}^{-{1}}$ , respectively, for structures with an interelectrode distance of 30 $\mu \text{m}$ at an applied voltage of 10 V and exposure to radiation with a wavelength of 235 nm. The high values of the photoelectric characteristics were caused by the manifestation of an internal gain of the photoresponse due to the self-localization of holes in $\alpha $ -Ga2O3. The prospects of researches to develop UVC radiation detectors for wireless UVC communication were shown.

AbstractThe structural and electrical properties of undoped and Sn doped κ‐Ga2O3 layers grown by epitaxial lateral overgrowth on TiO2/sapphire substrates using stripe and point masks show that the crystalline structure of the films can be greatly improved relative to conventional planar growth. The undoped films are semi‐insulating, with the Fermi level pinned near EC‐0.7 eV, and deep electron traps at EC‐0.5 eV and EC‐0.3 eV are detectable in thermally stimulated current and photoinduced current transient spectra measurements. Low concentration Sn doping results in net donor concentrations of ≈ 1013 cm−3, and deep trap spectra determined by electron traps at EC‐0.5 eV, and deep acceptors with an optical ionization threshold near 2 and 3.1 eV. Treatment of the samples in hydrogen plasma at 330 °C increases the donor density near the surface to ≈ 1019 cm−3. Such samples show strong persistent photocapacitance and photoconductivity, indicating the possible DX‐like character of the centers involved. For thin (5 µm) κ‐Ga2O3 films grown on GaN/sapphire templates, p‐type‐like behavior is unexpectedly observed in electrical properties and we discuss the possible formation of a 2D hole gas at the κ‐Ga2O3/GaN interface.

In this study, the structural and electrical properties of orthorhombic κ-Ga2O3 films prepared using Halide Vapor Phase Epitaxy (HVPE) on AlN/Si and GaN/sapphire templates were studied. For κ-Ga2O3/AlN/Si structures, the formation of two-dimensional hole layers in the Ga2O3 was studied and, based on theoretical calculations, was explained by the impact of the difference in the spontaneous polarizations of κ-Ga2O3 and AlN. Structural studies indicated that in the thickest κ-Ga2O3/GaN/sapphire layer used, the formation of rotational nanodomains was suppressed. For thick (23 μm and 86 μm) κ-Ga2O3 films grown on GaN/sapphire, the good rectifying characteristics of Ni Schottky diodes were observed. In addition, deep trap spectra and electron beam-induced current measurements were performed for the first time in this polytype. These experiments show that the uppermost 2 µm layer of the grown films contains a high density of rather deep electron traps near Ec − 0.3 eV and Ec − 0.7 eV, whose presence results in the relatively high series resistance of the structures. The diffusion length of the excess charge carriers was measured for the first time in κ-Ga2O3. The film with the greatest thickness of 86 μm was irradiated with protons and the carrier removal rate was about 10 cm−1, which is considerably lower than that for β-Ga2O3.

The electrical conductivity of pseudohexagonal ε(κ)‐Ga 2 O 3 films under different ambient gases (H 2 , NO 2 , O 2 , and CO) is studied in a range of temperatures from 400 to 550 °C. The exposure of ε(κ)‐Ga 2 O 3 to reducing gases such as H 2 and CO results in a reversible increase in current and conductance. The exposure to the oxidizing gases such as NO 2 and O 2 has the opposite effect. The maximum response to reducing gases (H 2 and CO) is observed at 500 °C and to oxidizing gases at 550 and 450 °C for NO 2 and O 2 , respectively. The highest sensitivity to H 2 is achieved at low applied voltages (≤7.9 V). In contrast, the highest sensitivity to NO 2 is observed at high applied voltages. The response and recovery times and temporal drift of ε(κ)‐Ga 2 O 3 characteristics under different ambient are estimated. Polycrystalline ε(κ)‐Ga 2 O 3 exhibits the semiconducting mechanism of electron transport at high temperatures. A qualitative model of the gas‐sensing effect based on the modulation of electron concentration near the surface region of ε(κ)‐Ga 2 O 3 due to the chemisorption of gas molecules is described. Tin doping of ε(κ)‐Ga 2 O 3 increases the response to H 2 at the temperature range from 25 to 550 °C.

We report on growth and electrical properties of α-Ga2O3 films prepared by halide vapor phase epitaxy (HVPE) at 500 °C on α-Cr2O3 buffers predeposited on sapphire by magnetron sputtering. The α-Cr2O3 buffers showed a wide microcathodoluminescence (MCL) peak near 350 nm corresponding to the α-Cr2O3 bandgap and a sharp MCL line near 700 nm due to the Cr+ intracenter transition. Ohmic contacts to Cr2O3 were made with both Ti/Au or Ni, producing linear current–voltage (I–V) characteristics over a wide temperature range with an activation energy of conductivity of ∼75 meV. The sign of thermoelectric power indicated p-type conductivity of the buffers. Sn-doped, 2-μm-thick α-Ga2O3 films prepared on this buffer by HVPE showed donor ionization energies of 0.2–0.25 eV, while undoped films were resistive with the Fermi level pinned at EC of 0.3 eV. The I–V and capacitance–voltage (C–V) characteristics of Ni Schottky diodes on Sn-doped samples using a Cr2O3 buffer indicated the presence of two face-to-face junctions, one between n-Ga2O3 and p-Cr2O3, the other due to the Ni Schottky diode with n-Ga2O3. The spectral dependence of the photocurrent measured on the structure showed the presence of three major deep traps with optical ionization thresholds near 1.3, 2, and 2.8 eV. Photoinduced current transient spectroscopy spectra of the structures were dominated by deep traps with an ionization energy of 0.95 eV. These experiments suggest another pathway to obtain p–n heterojunctions in the α-Ga2O3 system.

Herein, the influence of the oxygen flow on the formation of metastable polymorphs of gallium oxide (Ga 2 O 3 ) grown by halide vapor phase epitaxy (HVPE) on c‐plane patterned sapphire substrates (PSS), on gallium nitride (GaN) templates, and on m‐plane smooth sapphire substrates is reported. X‐ray diffraction, scanning electron microscopy, and cathodoluminescence are used to identify different polymorphic phases. The samples deposited on bare PSS exhibit faceted growth of the α‐Ga 2 O 3 on the cones of the sapphire substrate and the formation of the κ‐Ga 2 O 3 between the cones. In contrast, growth on GaN templates results in hexagonal columns of κ‐Ga 2 O 3 which produce a continuous smooth layer upon coalescence. The growth of Ga 2 O 3 on m‐plane sapphire substrates results in overgrown pyramids of the α‐phase. For all types of substrates, the variation of the oxygen flow affects only the thickness and coalescence of Ga 2 O 3 layers. Thus, the growth of Ga 2 O 3 metastable polymorphs is mainly influenced by the form, orientation, and symmetry of the substrate and shows a weak dependence on stoichiometry.

Heavily Sn-doped films of α -Ga 2 O 3 were grown by halide vapor phase epitaxy (HVPE) on basal plane c-sapphire and on (10-12) r-sapphire substrates with and without α -Cr 2 O 3 thin buffers prepared by magnetron sputtering and annealing in air at 500 °C for 3 h. For both substrate orientations, the use of α -Cr 2 O 3 buffers led to three major effects. The first was a substantial decrease of the half-width of the symmetric and asymmetric x-ray reflections. The second was an order of magnitude decrease of the net donor concentration produced by flowing the same amounts of Sn into the reactor. Third, there was a reduction in the concentration of the major electron trap in the films near E c − 1 eV by more than a factor of two. These results show the major influence of sapphire substrate orientation on the electrical and structural properties of α -Ga 2 O 3 grown by HVPE.

The growth of cubic and rhombohedral In 2 O 3 and (InGa) 2 O 3 epitaxial films by halide vapor phase epitaxy (HVPE) is reported. The deposition is carried out at 625 °C using indium trichloride (InCl 3 ), gallium monochloride (GaCl), and O 2 precursors on (0001) sapphire substrates, HVPE‐grown Ga 2 O 3 /Al 2 O 3 and metal‐organic chemical vapor deposition (MOCVD)‐grown GaN/Al 2 O 3 templates. The HVPE growth of phase pure In 2 O 3 and (InGa) 2 O 3 with corundum structure is reported for the first time.

Films of Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on bulk heavily B-doped (001)-oriented diamond substrates using thin interlayers of Al2O3 deposited by HVPE or AlN/AlGaN deposited by metalorganic chemical vapor deposition. The growth with AlN/AlGaN was dominated by the formation of a highly conducting ɛ-phase with poor crystalline quality. For these samples, excessive leakage of Schottky diodes and of the Ga2O3/diamond heterojunction prevented meaningful electrical characterization. The film grown with the Al2O3 interlayer was mainly composed of (−201) β-Ga2O3 with an admixture of the ɛ-phase. The film had a low density of residual shallow donors, 5 × 1015 cm−3, with deep electron traps spectra consisting of the well documented centers for β-Ga2O3 near Ec 0.27, Ec 0.7, and Ec 1 eV, all of which are often ascribed to native defects or their complexes. The electrical properties of heterojunctions were mostly determined by the properties of the Ga2O3 films. Both Schottky diodes and heterojunctions showed measurable photosensitivity for 259 nm wavelength excitation, but very low photocurrent for near-UV (365 nm wavelength excitation).

The growth of Ga(2)O(3)films by halide vapor phase epitaxy on plain and cone-shaped patterned sapphire substrates (PSS) is reported. The obtained specimens are characterized by X-ray diffraction, transmission electron microscopy, cathodoluminescence, optical transmission spectroscopy, and current-voltage measurements. Both types of Ga(2)O(3)layers are of reasonably high crystal qualities; their physical properties, however, are very different. Under the same conditions, the growth on plain substrates results in a continuous alpha-Ga(2)O(3)layer, whereas the growth on PSS produces a regular array of alpha-Ga(2)O(3)columns on top of the sapphire cones with the space between them filled with epsilon-Ga2O3. Ga(2)O(3)films grown on plain sapphire are insulating; in contrast, Ga(2)O(3)films grown on PSS are conducting. It is found that the conductivity of Ga(2)O(3)on PSS follows the Arrhenius law with the activation energy of 0.33 eV. New luminescent bands for alpha- and epsilon-phases are found. Spectral components of the defect-related luminescence for alpha- and epsilon- phases are identified.

Three-wave diffraction has been measured for a set of GaN, AlN, AlGaN and ZnO epitaxial layers grown on c-sapphire. A Renninger scan for the primary forbidden 0001 reflection was used. For each of the three-wave combinations, θ-scan curves were measured. The intensity and angular width of both φ- and θ-scan three-wave peaks were analyzed. The experimental data were used to determine properties of the multiple diffraction pattern in highly distorted layers. It is shown that the FWHM of θ scans is highly sensitive to the structural perfection and strongly depends on the type of three-wave combination. The narrowest peaks are observed for multiple combinations with the largest l index of the secondary hkl reflection. An influence of the type of the dislocation structure on the θ-scan broadening was revealed. These experimental facts are interpreted by considering the scanning geometry in the reciprocal space and taking into account the disc-shaped reciprocal-lattice points. The total integrated intensities of all the three-wave combinations were determined and their ratios were found to be in only a qualitative agreement with the theory. For AlGaN layers, the presence of the nonzero 0001 reflection was revealed, in contrast to AlN and GaN films.