Influence of pumping uniformity on current tuning of the emission wavelength of InAsSb/InAsSbP diode lasers

An investigation was made of continuous tuning of the emission wavelength in two types of InAsSb/InAsSbP diode heterolasers: three-layer structures with combined electrical and optical confinement and five-layer structures with separate confinement. In three-layer structures the emission wavelength initially decreases by 2–4 Å with increasing current and then increases by 10–15 Å. In five-layer structures the emission wavelength mainly decreases. This difference is attributed to the better flow of carriers in the bulk of the active region in five-layer structures as compared with three-layer ones. Pis’ma Zh. Tekh. Fiz. 24, 77–84 (March 26, 1998)     

Long-wavelength uncooled sources of λ=5–6 μ radiation using graded-index InAsSb(P) layers grown by liquid-phase epitaxy

Graded-index p-n InAsSb/InAsSbP/InAs structures capable of emitting at the maximum of the spectral curve up to 5.4 μm with a half-width of ∼26 meV (∼0.6 μm) without cooling have been fabricated and studied. This is the longest-wavelength radiation obtained at room temperature in III–V structures grown by liquid-phase epitaxy and the band is the narrowest obtained for semiconductor spontaneous radiation sources. Pis’ma Zh. Tekh. Fiz. 24, 88–94 (March 26, 1998)     

Influence of local pressure on the current-voltage characteristic of Au-Si〈Ni〉-Sb structures

Results of an investigation of the influence of local pressure on the current-voltage characteristic of Au-Si〈Ni〉-Sb structures are presented for the first time. It is shown that nickel impurities in the silicon increase the total strain sensitivity n-Si〈Ni〉 structures. Pis’ma Zh. Tekh. Fiz. 23, 62–64 (May 12, 1997)     

Hysteresis of the current-voltage characteristics of porous-silicon light-emitting structures

A new hysteresis effect is described in metal-porous-silicon-p-type silicon structures and a new model is proposed to describe current flow in these structures. Pis’ma Zh. Tekh. Fiz. 23, 59–65 (June 12, 1997)     

Bolometric properties of silicon thin-film structures fabricated by plasmachemical vapor-phase deposition

A method of fabricating uncooled thermally sensitive sandwich structures based on amorphous hydrated silicon films is discussed and experimental results are reported. The structures have an area of 10⁻⁴ cm², a resistance of ≅10 kΩ, and a temperature coefficient of resistance ≃2%/K. At 30 Hz and a current of ≃1 μA, the excess noise exceeds the thermal resistance noise by a factor of 1.7. Pis’ma Zh. Tekh. Fiz. 23, 63–68 (June 26, 1997)     

Enhancement of the efficiency of i-n-GaN light-emitting diodes by electrochemical etching

An investigation was made of the electrochemical etching of i-n-GaN light-emitting diode structures in aqueous solutions of KOH and NaOH to remove parasitic low-resistivity layers and inclusions in the structures which shunt the active current flow channels through the structures and lower the electroluminescence intensity. The electroluminescence intensity of the structures increased by two or three orders of magnitude during the etching process. Pis’ma Zh. Tekh. Fiz. 25, 55–60 (January 26, 1999)     

Functional properties of silicon/non-native-oxide heterostructures

It is shown possible to use Al/SnO₂/Si and Al/WO₃/Si metal-oxide-semiconductor structures as photodiodes with a large-area heterojunction. For structures with a film of amorphous tungsten trioxide (a-WO₃) they show promise for applications associated with the development of varicaps and photovaricaps and also chemical sensors of the capacitance type. Pis’ma Zh. Tekh. Fiz. 23, 7–13 (June 26, 1997)     

Nature of the transitional region during the deposition of titanium boride and nitride films on gallium arsenide

Photoluminescence and x-ray photoelectron spectroscopy methods were used to analyze the compositions of the near-junction regions of titanium boride (nitride)-gallium arsenide heterostructures. Data have been obtained for the first time on the formation of Ga_xB1_−x As and GaAs_xN_1−x solid solutions, which play an important role in the formation of the properties and the thermal stability of the experimental structures on the interphase boundary of these structures. Pis’ma Zh. Tekh. Fiz. 25, 71–76 (October 12, 1999)     

Modifications of spider silk sequences in an attempt to control the mechanical properties of the synthetic fibers

Bacteria were genetically engineered to produce two spider silk protein variants composed of basic repeat units combining a flagelliform elastic motif ([GPGGX]₄) and a major ampullate silk strength motif ([linker/poly-alanine]. The secondary structures of the pure recombinant proteins in solution were determined by circular dichroism. The data presented suggest that the nature of the 5th and 10th amino acid (X) in the [GPGGX]₂ elastic motif and temperature have an impact on the amount of β-sheet structures present in the proteins. More specifically, increasing temperatures seem to be positively correlated with β-sheet formation for both proteins and this state is irreversible or reversible when both X (5th and 10th) in the elastic motif are hydrophilic or hydrophobic respectively. Moreover, each pure silk-like protein was able to spontaneously self-assemble into films from aqueous solutions. Two kinds of synthetic fibers were made by pulling fibers from these preassembled films as well as spinning fibers from each protein resolubilized in HFIP. The mechanical data show that the pulled fibers are far tougher than the spun fibers suggesting a better fiber organization. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hydrogen-Bonded Structure of 2:1 TCNQ Salt of 2-Methyl-5-Phenyl-7,9-Dichloro-1,6-Diazaphenalene

The crystal structure of 2:1 TCNQ salt of 2-methyl-5-phenyl-7,9-dichloro-1,6-diazaphenalene (1) was investigated for the construction of new hydrogen-bonded charge-transfer complexes. This salt was composed of neutral 1, protonated 1 (1·H ⁺) and ionic TCNQ (TCNQ^{· −}), and constructed a segregated structure with uniform π-stackings. The N–H···N≡C hydrogenbonding between 1/1·H⁺ and TCNQ^{· −} formed the D-A-D triad, and connected the columnar structures.     

Photoluminescence of porous-silicon/diamondlike-carbon-film structures subjected to rapid thermal annealing

The influence of rapid thermal annealing on the photoluminescence properties of porous-silicon/diamondlike-carbon-film structures is investigated. Redistribution of the radiation from the long-wavelength to the short-wavelength region is discovered. Models of the processes observed are presented. Pis’ma Zh. Tekh. Fiz. 25, 27–32 (April 26, 1999)     

Electroluminescence of quantum-well structures on type-II InAs/GaSb heterojunctions

The electroluminescent properties of quantum-well diode structures on staggered type-II heterojunctions in the InAs/GaSb system, obtained by molecular-beam epitaxy on InAs substrates, are investigated. Electroluminescence is observed in the spectral range 3–4 μm at T=77 K. It is found that emission bands due to recombination transitions involving electrons from the size-quantization levels of both the self-matched quantum wells at the InAs/GaSb type-II heterojunction and of the square quantum wells in short-period superlattices. Pis’ma Zh. Tekh. Fiz. 24, 50–56 (June 26, 1998)     

Control of the morphology of n-type porous silicon

The morphology of layers obtained by anodic etching is related to the current-voltage characteristics of the electrolytic cell during the etching. By etching at various points of the current-voltage characteristic one can obtain porous silicon with various structures. Pis’ma Zh. Tekh. Fiz. 23, 80–84 (March 26, 1997)     

Investigation of the photoluminescence and modification of InGaP/GaAs/InGaAs heterostructures by near-field scanning microscopy

This study deals with the local spectroscopy and modification of semiconducting InGaP/GaAs/InGaAs quantum-well heterostructures by near-field scanning optical microscopy. The spatial distribution of the photoluminescence intensity in these structures is investigated and spatial nonuniformity of the photoluminescence is observed as a result of the nonuniform properties of the InGaP layers. It is shown for the first time that local quenching of the photoluminescence may be achieved by optically induced impurity diffusion near the quantum well, and this may be utilized to develop low-dimension semiconducting devices. Pis’ma Zh. Tekh. Fiz. 23, 20–25 (August 26, 1997)     

New potential applications of scanning electron microscopy to studying InAsSb/InAsSbP lasers

New potentials are demonstrated for the application of scanning electron microscope methods to identifying heteroboundaries, monitoring the sharpness of interfaces, and determining the positions of _p-n junctions in laser structures based on InAsSb/InAsSbP, including at low temperatures. The method permits optimization of the parameters of long-wavelength lasers and to obtain record low threshold currents (I_th≤25 mA at _T=77 K) for lasing wavelengths λ=3–3.5 μm. Pis’ma Zh. Tekh. Fiz. 23, 54–60 (March 26, 1997)     

Infrared laser (λ=3.2 μm) based on broken-gap type II heterojunctions with improved temperature characteristics

Laser structures based on broken-gap type II p-GaInAsSb/n-InGaAsSb heterojunctions in the active region are proposed and studied. Lasing at 3.2–3.4 μm has been obtained in the temperature range 77–195 K with a threshold current density of 400 A/cm² at 77 K and a characteristic temperature T₀=47 K. Pis’ma Zh. Tekh. Fiz. 23, 55–60 (February 26, 1997)     

Photovoltaic properties of semiconductor-protein heterocontacts

It is found that heterocontacts consisting of a semiconductor (e.g., InSe) and a natural protein exhibit a broad-band photovoltaic effect and do not display an appreciable shortwavelength drop in the spectral range from 1.2 to 3.7 eV. The maximum photosensitivity of such structures, which reaches 2 mA/W at T=300 K, is observed when they are illuminated on the protein side. It is concluded that the structures created can be employed as broad-band photosensors of optical radiation. Pis’ma Zh. Tekh. Fiz. 25, 76–80 (April 26, 1999)     

Conditions for the existence of backward surface magnetostatic waves in a ferrite-insulator-metal structure

A theoretical analysis is made of the dispersion of surface magnetostatic waves (SMSWs) at different frequencies propagating in ferrite-insulator-metal (FIM) structures magnetized by a uniform magnetic field. It is established that depending on the ratio between the thicknesses of the ferrite and insulating layers in FIM structures, backward SMSWs exist in different frequency ranges and have different wave numbers and directions of propagation. The conditions for which backward SMSWs may be observed directly in FIM structures are determined. Pis’ma Zh. Tekh. Fiz. 24, 1–7 (July 12, 1998)     

Dislocation structures of low-angle boundaries in Nb-doped SrTiO3 bicrystals

Dislocation core structures in low-angle boundaries of Nb-doped SrTiO₃ bicrystals were investigated by high-resolution electron microscopy. Bicrystals with tilt angles of 2°, 4°, 6° and 8° with respect to the [001] zone axis were prepared by joining two single crystals at 1873 K. All of the boundaries consisted of a regular array of dislocations whose spacing gradually decreased with an increase in tilt angle. Except for the 2° tilt-angle boundary, the dislocation cores exhibited a dissociation from a[010] into two partials of a/2[010] on (100). Furthermore, two kinds of dislocation core structures were observed; Sr–Sr atomic columns and Ti–O atomic columns inside the cores. In addition, it was found that the positioning of adjacent cores along the boundary tended to change from a linear form to a zig-zagg shape as the tilt angle was increased from 4° to 8°. In the case of the linear array, dislocation core structures including Sr–Sr columns or Ti–O columns alternately appear. In contrast, only one core structure was observed in the zig-zagged array. On the other hand, the dislocation cores in the 2°-tilt-angle boundary had another type of dissociation with a/2[110] or a/2[111] partials, which included the twist component at a tilt axis of [001].     

Self-organization of quantum dots in multilayer InAs/GaAs and InGaAs/GaAs structures by submonolayer migration-stimulated epitaxy

Multilayer structures of InGaAs/GaAs quantum dots fabricated by submonolayer migrationstimulated epitaxy have been studied experimentally by scanning tunneling microscopy and results are presented. These results clearly show that in multilayer structures, ordering of nanoobjects into rows occurs in InAs and InGaAs heteroepitaxial layers. Pis#x2019;ma Zh. Tekh. Fiz. 23, 80–84 (November 26, 1997)