Avalanche photodiodes have emerged as a promising technology with significant potential for various medical applications. This article presents an overview of the advancements and applications of avalanche photodiodes in the field of medical imaging. Avalanche photodiodes offer distinct advantages over traditional photodetectors, including a higher responsivity, faster response times, and superior signal-to-noise ratios. These characteristics make avalanche photodiodes particularly suitable for medical-imaging modalities that require a high detection efficiency, excellent timing resolution, and enhanced spatial resolution. This review explores the key features of avalanche photodiodes, discusses their applications in medical-imaging techniques, and highlights the challenges and future prospects in utilizing avalanche photodiodes for medical purposes. Special attention is paid to the recent progress in silicon-compatible avalanche photodiodes.

The use of CH₄ as an energy source is increasing every day. To increase the efficiency of CH₄ combustion and ensure that the equipment meets ecological requirements, it is necessary to measure the CH₄ concentration in the exhaust gases of combustion systems. To this end, sensors are required that can withstand extreme operating conditions, including temperatures of at least 600 °C, as well as high pressure and gas flow rate. ZnGa₂O₄, being an ultra-wide bandgap semiconductor with high chemical and thermal stability, is a promising material for such sensors. The synthesis and investigation of the structural and CH₄ sensing properties of ceramic pellets made from pure and Er-doped ZnGa₂O₄ were conducted. Doping with Er leads to the formation of a secondary Er₃Ga₅O₁₂ phase and an increase in the active surface area. This structural change significantly enhanced the CH₄ response, demonstrating an 11.1-fold improvement at a concentration of 10⁴ ppm. At the optimal response temperature of 650 °C, the Er-doped ZnGa₂O₄ exhibited responses of 2.91 a.u. and 20.74 a.u. to 100 ppm and 10⁴ ppm of CH₄, respectively. The Er-doped material is notable for its broad dynamic range for CH₄ concentrations (from 100 to 20,000 ppm), low sensitivity to humidity variations within the 30–70% relative humidity range, and robust stability under cyclic gas exposure. In addition to CH₄, the sensitivity of Er-doped ZnGa₂O₄ to other gases at a temperature of 650 °C was investigated. The samples showed strong responses to C₂H₄, C₃H₈, C₄H₁₀, NO_2, and H₂, which, at gas concentrations of 100 ppm, were higher than the response to CH₄ by a factor of 2.41, 2.75, 3.09, 1.16, and 1.64, respectively. The study proposes a plausible mechanism explaining the sensing effect of Er-doped ZnGa₂O₄ and discusses its potential for developing high-temperature CH₄ sensors for applications such as combustion monitoring systems and determining the ideal fuel/air mixture.

This paper presents the results of studying the processes of epitaxial growth of germanium on silicon with crystallographic orientation (111) in a wide temperature range. The temperature dependences of the duration of the transition stage from the 7 × 7 to 5 × 5 superstructure and the values of the critical thickness of the transition from two-dimensional to three-dimensional growth in the range from 250 to 700 °C are determined using the reflection high-energy electron diffraction method. It was shown for the first time that the transition time from the 7 × 7 superstructure to 5 × 5 superstructure depends on the temperature of epitaxial growth. The region of low temperatures of synthesis, which has received insufficient attention so far, is also considered.

Two-dimensional silicon (silicene) and germanium (germanene) have attracted special attention from researchers in recent years. At the same time, highly oriented pyrolytic graphite (HOPG) and graphene are some of the promising substrates for growing silicene and germanene. However, to date, the processes occurring during the epitaxial growth of silicon and germanium on the surface of such substrates have been poorly studied. In this work, the epitaxial growth of silicon and germanium is studied directly during the process of the molecular beam epitaxy deposition of material onto the HOPG surface by reflection high-energy electron diffraction (RHEED). In addition, the obtained samples are studied by Raman spectroscopy and scanning electron microscopy. A wide range of deposition temperatures from 100 to 800 °C is considered and temperature intervals are determined for various growth modes of silicon and germanium on HOPG. Conditions for amorphous and polycrystalline growth are distinguished. Diffraction spots corresponding to the lattice constants of silicene and germanene are identified that may indicate the presence of areas of graphene-like 2D phases during epitaxial deposition of silicon and germanium onto the surface of highly oriented pyrolytic graphite.

Subject of study. The work studied the formation of germanium quantum dots on silicon with (100) crystallographic orientation under different growth regimes. Aim of study. The work is devoted to conducting experimental studies of the influence of growth mechanisms on the formation of germanium layers and quantum dots on a silicon (100) substrate for the production of optical elements based on silicon-germanium nanostructures. Methods. After pre-epitaxial cleaning of the Si substrate, germanium is synthesized on Si(100) through molecular beam epitaxy. The surface morphology is analyzed using reflection high-energy electron diffraction during synthesis and scanning electron microscopy after deposition. Main results. The work determines the temperature ranges at which the Si/Si(100) growth occurs due to the nucleation of islands, due to the movement of steps, and in combination. The effect of changing growth mechanisms on the size and density of Ge quantum dots on Si(100) is shown. Practical significance. The research results provide insight into the influence of growth mechanisms on the sizes of formed germanium quantum dots on silicon, which will make it possible to create nanophotonics and nanoelectronics elements with strictly specified parameters.

The dynamics of initial layer-by-layer growth and subsequent nucleation of quantum dots of Si and Ge on Si(001) were studied combining reflection high-energy electron diffraction, scanning electron microscopy and atomic force microscopy. It was shown that the processes occurring at the initial stage determine further growth of the heterostructure and final shape and density of nanoislands. The mechanisms of terrace formation, occurrence and dynamics of dimer rows of the 2 × N superstructure, and effects of temperature on the growth characteristics were described. The obtained experimental dependences show the critical relationship between the synthesis parameters (growth temperature), epitaxial growth processes and the characteristics of the resulting nanoislands. The fundamental studies conducted make it possible to create self-organizing quantum dots of a given size and density for advanced optoelectronics, including infrared photosensitive elements and single-photon detectors.