Конструкции блокирующих слоев для подавления паразитной рекомбинации в мощных диодных лазерах с GaAs волноводом

Using numerical simulation, a search is carried out for designs of asymmetric barrier layers (ABLs) for a laser diode having GaAs waveguide and emitting at the wavelength λ = 980 nm. A pair of ABLs, adjoining the active region on both sides, blocks undesired charge carrier flows and suppresses parasitic spontaneous recombination in the waveguide layers. Optimal designs of ABLs based on AlGaAsSb and GaInP for blocking electrons and holes, respectively, are proposed that make it possible to reduce the parasitic recombination current down to less than 1% of the initial value. To suppress electron transport, an alternative structure based on three identical AlInAs barriers is also proposed. The GaAsP spacers separating these barriers from each other have different thicknesses. Due to this, its own set of quasi-bound (resonant) states is formed in each spacer that is different from the neighbor spacer set of states. As a result of this, the resonant tunneling channels are blocked: the parasitic electron flow is reduced by several tens of times in comparison with the case of spacers of equal thickness.

Analyzing metallurgical interaction during arc surfacing of barrier layers on titanium to prevent the formation of intermetallics in titanium-steel compounds

This paper considers a possibility to obtain high-quality butt junctions of bimetallic sheets from steel clad with a layer of titanium, with the use of barrier layers. The task that was tackled related to preventing the formation of Ti-Fe intermetallic phases (IMPs) between the steel and titanium layer. The barrier layers (height ~0.5 mm) of vanadium and copper alloys were surfaced by arc techniques while minimizing the level of thermal influence on the base metal. To this end, plasma surfacing with a current-driving wire and pulsed MAG surfacing were used. The obtained samples were examined by methods of metallography, X-ray spectral microanalysis, durometric analysis. It has been established that when a layer of vanadium is plated on the surface of titanium, a defect-free structure of variable composition (53.87–65.67) wt % Ti with (33.93–45.54) wt % V is formed without IMPs. The subsequent surfacing of steel on a layer of vanadium leads to the formation of eutectics (hardness up to 5,523 MPa) in the fusion zone, as well as to the evolution of cracks. To prevent the formation of IMPs, a layer of bronze CuBe2 was deposited on the surface of vanadium. The formed layer contributed to the formation of a grid of hot cracks. In the titanium-vanadium-copper transition zones (0.1–0.2 mm wide), a fragile phase was observed. To eliminate this drawback, the bronze CuBe2 was replaced with bronze CuSi3Mn1; a defect-free junction was obtained. When using a barrier layer with CuSi3Mn1, a defect-free junction was obtained (10–30 % Ti; 18–50 % Fe; 5–25 % Cu). The study reported here makes it possible to recommend CuSi3Mn1 as a barrier layer for welding bimetallic sheets "steel-titanium". One of the applications of the research results could be welding of longitudinally welded pipes of main oil and gas pipelines formed from bimetallic sheets of steel clad with titanium.