Characterization of quantum-confinement whispering-gallery-mode lasers operating above room temperature

The temperature dependence of the threshold current density and emission spectra of disk-shaped quantum-confinement lasers operating on whispering-gallery modes has been studied in the 23?C180°C interval. As the temperature is increased in this interval, the radiation wavelengths grows from 2.24 to 2.42 ??m, stable lasing is observed up to 177°C, and the threshold current exhibits exponential growth in proportion to exp(T/T ₀) with T ₀ = 70 K.     

Early detection algorithm for attacks against information resources of automatic manufacturing control systems

A certain model of organizing protection mechanisms in distributed information system is proposed; implementation of the model allows for improving both time-related and probabilistic characteristics of protection systems. In addition, new detection algorithm for attacks against resources of information system is suggested based on the notion of critical threat domain.     

Anisotropic polarization of radiation in quantum-confinement whispering-gallery-mode lasers

The polarization of lasing and spontaneous emission from half-disk- and disk-shaped quantum-confinement lasers operating on whispering-gallery modes with wavelengths within 2.18–2.28 μm has been studied. It is established that electric vector E of output radiation is oriented predominantly in the p-n junction plane, which is explained by the fact that radiation is generated due to electron-heavy hole transitions. Modulation of the polarized spontaneous radiation spectra has been observed.     

Warping a single Mn acceptor wavefunction by straining the GaAs host

Transition-metal dopants such as Mn determine the ferromagnetism in dilute magnetic semiconductors such as Ga(1-x)Mn(x)As. Recently, the acceptor states of Mn dopants in GaAs were found to be highly anisotropic owing to the symmetry of the host crystal. Here, we show how the shape of such a state can be modified by local strain. The Mn acceptors near InAs quantum dots are mapped at room temperature by scanning tunnelling microscopy. Dramatic distortions and a reduction in the symmetry of the wavefunction of the hole bound to the Mn acceptor are observed originating from strain induced by quantum dots. Calculations of the acceptor-state wavefunction in the presence of strain, within a tight-binding model and within an effective-mass model, agree with the experimentally observed shape. The magnetic easy axes of strained lightly doped Ga(1-x)Mn(x)As can be explained on the basis of the observed local density of states for the single Mn spin.     

Infrared whispering-gallery-mode lasers (λ= 2.4 μm) with convex disk cavity operating at room temperature

A whispering gallery mode (WGM) semiconductor laser with a convex disk cavity operating at room temperature in the middle-IR range (λ = 2.4 μm) has been created for the first time. The convex cavity was formed by etching in a specially selected CrO₃-HF-H₂O mixture. The room-temperature emission spectra have been measured. The laser generates WGMs at room temperature in a pulsed regime.     

Electronic properties of n-ZnO(Al)/p-Si heterojunction prepared by dc magnetron sputtering

The electronic properties of the interface between p-type Si and Al-doped ZnO have been investigated. Films of ZnO(Al) with a thickness of 300 nm were deposited at room temperature by dc magnetron sputtering and subsequently subjected to heat treatment in air in the temperature range 100-400 °C. Current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements were used to characterize the electrical properties of the heterostructure. The I-V measurements show a diode-like behavior with a rectification of ~ 3-4 orders of magnitude. However, annealing above 200 °C gives rise to a pronounced recombination/generation current in the depletion region, which correlates with an increase of the carrier concentration close to the interface and indicates defect formation. Indeed, DLTS reveals the presence of two prominent defect states, one at 0.38 eV above the valence band edge (E_v), and the other, formed during the heat treatment above 250 °C, around E_v + 0.43 eV, which is consistent with the I-V and C-V data.