Mid-infrared GaSb-based EP-VCSELl emitting at 2.63 μm

Electrically-pumped GaSb-based vertical-cavity surface-emitting lasers emitting up to 2.63 μm at room temperature are reported. The whole structure was grown monolithically in one run by solid-source molecular beam epitaxy. This heterostructure is composed of two n-doped AlAsSb/GaSb DBRs, a type-I GaInAsSb/AlGaAsSb multiquantum- well active region and an InAsSb/GaSb tunnel junction. A quasi-CW (1 μs, 5 %) operation was obtained at room temperature for 35 μm-diameter devices with threshold current of 85 mA.     

GaInAsSb/GaSb pn photodiodes for detection to 2.4 mu m

Ga/sub 0.77/In/sub 0.23/As/sub 0.20/Sb/sub 0.80//GaSb pn heterojunction photodiodes have been prepared by liquid phase epitaxy. They exhibit a long-wavelength threshold of 2.4 mu m. The room-temperature dark current at V=-0.5 V is 3 mu A (10 mA/cm/sup 2/) and the external quantum efficiency is around 40% in the wavelength range 1.75-2.25 mu m. The estimated detectivity D* at 2.2 mu m is 8.8*10/sup 9/ cm Hz/sup 1/2/ W/sup -1/.<>     

New III-V double-heterojunction laser emitting near 3.2 μm

Double heterostructure lasers based on the InAsSbP/InAsSb system have been prepared by liquid phase epitaxy. They operate at 78 K near 3.2 μm, with a threshold current density of 4.5 kA/cm² in pulsed conditions. The characteristic temperature T₀ is 30 K     

Effect of nitrogen on the band structure and material gain of In/sub y/Ga/sub 1-y/As/sub 1-x/N/sub x/-GaAs quantum wells

The conduction subband structure of InGaAsN-GaAs quantum wells (QWs) is calculated using the band anticrossing model, and its influence on the design of long-wavelength InGaAsN-GaAs QW lasers is analyzed. A good agreement with experimental values is found for the QW zone center transition energies. In particular, a different dependence of the effective bandgap with temperature when compared to the equivalent N-free structure is predicted by the model and experimentally observed. A detailed analysis of the conduction subband structure shows that nitrogen strongly decreases the electron energies and increases the effective masses. A very small N incorporation is also found to increase the nonparabolicity, but this effect saturates for higher nitrogen contents. Both the In content and well width decrease the effective masses and nonparabolicity of the conduction subbands. Material gain as a function of the injection level is calculated for InGaAsN-GaAs QWs for moderate carrier densities. The peak gain at a fixed carrier density is found to be reduced, compared to InGaAs, for a small N content, but this reduction tends to saturate when the N content is further increased. For the gain peak energy, a monotonous strong shift to lower energies is obtained for increasing N content, supporting the feasibility of 1.55-/spl mu/m emission from InGaAsN-GaAs QW laser diodes.     

Long-wavelength strained-layer InAs/GaInAs single-quantum-well laser grown by molecular beam epitaxy on InP substrate

Laser emission is reported for the first time from a 10 monolayer-wide highly strained (3.2%) InAs single quantum well confined by Ga/sub 0.47/In/sub 0.53/As layers. At 80 K the emission spectrum of broad-area laser diodes is centred at 1.836 mu m, the threshold current-density is approximately 500 A/cm/sup 2/ and the characteristic temperature is T/sub 0/ approximately=30 K. CW operation is achieved up to 110 K with narrow-stripe devices but at shorter wavelength, due to increased losses and filling of the quantum-well energy levels.<>     

Evaluation of the potential of ZnSe and Zn(Mg)BeSe compounds forultraviolet photodetection

We report on blue-violet and ultraviolet (UV) light detectors based on ZnSe and Zn(Mg)BeSe compounds lattice matched onto GaAs substrates. Three types, namely p-i-n, Schottky, and metal-semiconductor-metal (MSM) structures, have been fabricated. A comprehensive characterization of the spectral response is developed in each case. Performances, specifications, and advantages of each kind of device are detailed, p-i-n ZnBeSe-ZnMgBeSe photodiodes exhibit a high responsivity (0.17 A/W at 150 nm) and a high rejection rate (10⁴ ). Losses by recombination in the top p-type layer and p-type doping limitations lead to a decrease of the high energy response which is their major drawback. Thanks to the position of their depleted region on top of the structure. Schottky barriers and MSM photodetectors are much more suited for UV detection. With Schottky diodes, high efficiencies are obtained over the whole UV-A and -B ranges. Detectivity values above 10¹¹ mHz^1/2 W^-1 have been measured. MSM detectors appear as an attractive alternative to Schottky barrier diodes with as high a response and nearly as low noise levels. This study thus demonstrates the potential of ZnSe- and ZnMgBeSe-based Schottky barriers and MSM devices for efficient detection in the UV region     

Modelling and experimental study of the tertiary creep stage of Grade 91 steel

This article addresses experimental studies and analytical simulations of the tertiary creep stage of Grade 91 steel tested at various stresses and temperatures between 500°C (up to 160 × 10³ h) and 600°C (up to 94 × 10³ h). The strain rate increases after its minimum mainly because of the softening of the material which microstructure evolves strongly during creep deformation. An interrupted creep test shows that necking significantly affects the acceleration of the reduction in cross-section only during the last 10% of the creep lifetime. The Hoff model based on homogeneous reduction of cross-section correctly predicts lifetimes only for high applied stress. The Hart necking model using the Norton power-law allows fair predictions of lifetimes up to 60 × 10³ h at 500°C. The necking model using a modified Norton power-law combined with a material softening term allows predictions of lifetimes for all creep tests, differing from the experimental results by less than 50%, which is consistent with the experimental scatter. The evolution of the cross-section predicted by this model is in agreement with measurements carried out during the interrupted creep test. Two prediction rules for the lifetime prediction are deduced from the necking model that takes into account the material softening. For a large number of tempered martensitic steels, these two criteria bound the experimental lifetimes up to 200 × 10³ h at 500–700°C.