Influence of electrodes on the parameters of solar-blind detectors of UV radiation

The influence of the topology of electrodes on the electrical and photoelectric characteristics of metal–semiconductor–metal structures is studied. Gallium-oxide films are produced by the radio-frequency magnetron-assisted sputtering of a Ga2O3 target onto (0001)-oriented sapphire substrates. Two types of electrodes are formed on the surface of the oxide films. The first type corresponded to two parallel electrodes spaced by an interelectrode distance of 250 μm, and the second type to interdigitated electrodes. In the case of the second type of electrodes, the distance between the “fingers” is 50, 30, 10, and 5 μm. The structures possess sensitivity to ultraviolet radiation at a wavelength of λ = 254 nm, irrespective of the type of contact. The second type of detectors with an interelectrode distance of 5 μm show the largest photocurrents, Iph = 3.8 mA, and a specific detectivity of D* = 5.54 × 1015 cm Hz0.5 W–1

Investigation of the persistence conductivity and photoelectric characteristics in detectors with interdigital electrodes based on β-Ga2O3

Herein, the electrical and photoelectric characteristics of solar-blind UV detectors based on β-Ga2O3 films with interdigital electrodes are presented. The sensors with interdigital electrodes have interelectrode spacing d = 5, 10, 30, and 50 μm. The structures exhibit high sensitivity to ultraviolet radiation with a wavelength of λ = 254 nm. The detectors with the smallest interelectrode spacing (5 μm) demonstrate the highest photocurrent value. The detectors have a saturation region on the current–voltage characteristics under UV irradiation, which shifts to the region of lower voltages with decreasing interelectrode spacing. A mechanism to explain the presence of the saturation region on the I–V characteristic is proposed. The sensors exhibit high value of a persistence photoconductivity, which decreases exponentially with an estimated value of the time constant t 1 = 59–63 s

Morphological Changes in the Dental Pulp of Experimental Animals in the Treatment of Acute Partial Pulpitis using Modern Materials

Aim. To study the morphological changes in the tooth pulp of experimental animals when modelling acute partial pulpitis using calcium silicate modified with light-cured resin and calcium hydroxide.Materials and methods. An experimental model of acute partial pulpitis was applied including the formation of a cavity on the lingual surface of the tooth, which corresponded to advanced caries in terms of depth, followed by a slight perforation up to the tooth pulp with a sharp probe. This model of acute partial pulpitis was reproduced for 32 teeth in four sexually mature rams. The teeth were extracted together with the surrounding sockets 15, 30 and 90 days after the modelling of pulpitis, followed by their fi xation in 10% solution of neutral formalin. Decalcification was performed in 25% solution of Trilon B. The material was poured into celloidin; histological sections were stained with hematoxylin and eosin according to Masson’s trichrome procedure.Results. The histological examination of pulp from the main group (calcium silicate modified with light-cured resin) revealed the formation of a biological barrier from secondary dentin in the area of the cavity and perforation up to the pulp chamber on the 90th day after the experiment started. The tooth pulp revealed no signs of an inflammatory process. On the 90th day after the experiment started, no pronounced morphological changes in the main substance and dentinal tubules in the area of the cavity walls were noted in the coronal pulp of experimental animals from the comparison group (calcium hydroxide). A focal chronic inflammatory process was noted in the tooth pulp.Conclusion. It was established that the use of calcium silicate modified with light-cured resin in the experimentally created model of acute partial pulpitis was accompanied by the formation of a biological barrier and a well-developed zone of reparative dentin in the area of the cavity and perforation up to the pulp chamber, as compared to the group where calcium hydroxide was used. Thus, the study results confirmed the efficay of using calcium silicate modified with light-cured resin within the biological method for treating acute partial pulpitis, which shortens the functional recovery of tooth pulp

Self-powered photo diodes based on Ga2O3/n-GaAs structures

The electrical and photovoltaic characteristics of the Ga2O3/n-GaAs structures have been studied. A gallium oxide film was obtained by HF magnetron sputtering on n-GaAs epitaxial layers with concentration of N_d=9.5·1014 cm-3. The thickness of the oxide film was 120 nm. Measurements at a frequency of 106 Hz have shown that the capacitance-voltage and conductance-voltage dependences are described by curves characteristic of metal-insulator-semiconductor structures and exhibit low sensitivity to radiation with λ=254 nm. When operating on a constant signal, the samples exhibit the properties of a photodiode and are able to work offline. The photoelectric characteristics of the detectors during continuous exposure to radiation with λ=254 nm are determined by the high density of traps at the Ga2O3/GaAs interface and in the oxide film. Keywords: MIS-structures, capacitance-voltage characteristics, volt-siemens characteristics, photocurrent, trap density