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Dynamic characteristics of low-voltage AlGaAs/GaAs heterostructure N-p-N phototransistors operating in the high-current mode have been studied. It was found that, above critical voltages, the turn-on process of a phototransistor consists of two phases separated in space and time. It is shown that the power of an optical-activation source affects the turn-on delay of the phototransistor and has no effect on the maximum current. An analysis of the spatial current dynamics in the plane of the collector p-n junction demonstrated that the first phase of the turn-on process is localized in the optical activation (optical window) region. In this case, the region of current localization during the first phase may be smaller than the optical-activation region. It was found that the whole current during the second phase is localized at the boundary between the optical window and the ohmic contact. The turn-on delay of the second phase is associated with the carrier transport in the base layer from the optical-activation region to the boundary with the ohmic collector contact. [ABSTRACT FROM AUTHOR]

The results obtained demonstrate that the lasing dynamics reflects the current dynamics formed as a result of complex nonlinear couplings within the laser-thyristor heterostructure. The observed specific features mainly result from the appearance of new channels for generation of excess carriers in the p-base. These channels enhance the main optical activation channel formed by the photogeneration due to the absorption of the spontaneous emission from the active region of the laser part of the heterostructure. The additional channels of excess carrier generation may have an optical nature in the case of scattered laser light upon appearance of new high-Q modes. For nearly critical blocked voltages, generation of carriers can be initiated by an avalanche multiplication of photogenerated carriers. [ABSTRACT FROM AUTHOR]

In this manuscript, we attempt to clarify the capability of utilisation of α-FeSi2 nanocrystals as a buffer layer for growth of monocrystalline/high-quality β-FeSi2 direct-gap semiconductor from the point of view of the crystal lattice misfits and near coincidence site (NCS) lattices. Iron silicides-based nanostructures have a wide spectrum of possible industrial applications in different fields. Mainly, interest in these functional materials is caused by their ecological safety and Earth's core abundance that give us the opportunity for greener future with highly effective electronic devices. β-FeSi2 phase due to its allowed direct transition with energy close to 0.87 eV can be used as active material in light emission diodes (LED). Utilisation of buffer layers between silicon substrate and give one more tool to engineer the band structure of semiconducting β‑FeSi2 phase. We attempt to clarify the capability of the utilisation of the α-FeSi2 phase as a buffer layer for the growth of β-FeSi2 direct-gap semiconductor from the point of view of the crystal lattice misfits and near coincidence site (NCS) lattices. Possible β-FeSi2/α-,γ-,s-FeSi2/Si orientation relationships (ORs) and habit planes were examined with crystallogeometrical approaches and compared with β-FeSi2/Si ones. The lowest interplanar and interatomic spacing misfits between silicon lattice and a silicide one are observed for the pair of s-FeSi2{011}[200]/Si{022}[100] at room temperature and equal to –0.57%. The least interplanar and interatomic spacing misfit of 1.7 and 1.88%, respectively, for β-FeSi2/Si, can be decreased as low as –0.67 (interplanar) and 0.87 (interatomic) % by placing an α-FeSi2 layer between silicon and β-FeSi2 phase. It is stated that the growth of metastable γ-FeSi2 is also favourable on silicon due to low interplanar and interatomic spacing misfit (–0.77%) and a higher density of NCS in comparison with s-FeSi2. Design and technological procedure for the synthesis of possible β-FeSi2/α-FeSi2/Si heterostructure have been proposed based on the results obtained. [ABSTRACT FROM AUTHOR]

A pure crystallogeometrical approach is proposed for predicting orientation relationships, habit planes and atomic structures of the interfaces between phases, which is applicable to systems of low‐symmetry phases and epitaxial thin film growth. The suggested models are verified with the example of epitaxial growth of α‐, γ‐ and β‐FeSi2 silicide thin films on silicon substrates. The density of near‐coincidence sites is shown to have a decisive role in the determination of epitaxial thin film orientation and explains the superior quality of β‐FeSi2 thin grown on Si(111) over Si(001) substrates despite larger lattice misfits. Ideal conjunctions for interfaces between the silicide phases are predicted and this allows for utilization of a thin buffer α‐FeSi2 layer for oriented growth of β‐FeSi2 nanostructures on Si(001). The thermal expansion coefficients are obtained within quasi‐harmonic approximation from the DFT calculations to study the influence of temperature on the lattice strains in the derived interfaces. Faster decrease of misfits at the α‐FeSi2(001)||Si(001) interface compared to γ‐FeSi2(001)||Si(001) elucidates the origins of temperature‐driven change of the phase growing on silicon substrates. The proposed approach guides from bulk phase unit cells to the construction of the interface atomic structures and appears to be a powerful tool for the prediction of interfaces between arbitrary phases for subsequent theoretical investigation and epitaxial film synthesis. [ABSTRACT FROM AUTHOR]