Coronal magnetograms of solar active regions

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Influence of GaAs Substrate Orientation on InAs Quantum Dots: Surface Morphology, Critical Thickness, and Optical Properties

InAs/GaAs heterostructures have been simultaneously grown by molecular beam epitaxy on GaAs (100), GaAs (100) with a 2° misorientation angle towards [01−1], and GaAs (n11)B (n = 9, 7, 5) substrates. While the substrate misorientation angle increased from 0° to 15.8°, a clear evolution from quantum dots to quantum well was evident by the surface morphology, the photoluminescence, and the time-resolved photoluminescence, respectively. This evolution revealed an increased critical thickness and a delayed formation of InAs quantum dots as the surface orientation departed from GaAs (100), which was explained by the thermal-equilibrium model due to the less efficient of strain relaxation on misoriented substrate surfaces

Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm

InGaAs-InP DHBTs for increased digital IC bandwidth having a 391-GHz f(T) and 505-GHz f max

InP-In0.53Ga0.47As-InP double heterojunction bipolar transistors (DHBT) have been designed for use in high bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 391-GHz f(t), and 505-GHz f(max), which is the highest f(t) reported for an InP DHBT--as well as the highest simultaneous f(t) and f(max) for any mesa HBT. The devices have been aggressively scaled laterally for reduced base-collector capacitance Ccb. In addition, the base sheet resistance rho(s) along with the base and emitter contact resistivities rho(c) have been lowered. The DC current gain beta is approximate to 36 and BV,CEO = 5.1 V. The devices reported here employ a 30-nm highly doped InGaAs base, and a 150-nm collector containing an InGaAs-InAlAs superlattice grade at the base-collector junction. From this device design we also report a 142-GHz static frequency divider (a digital figure of merit for a device technology) fabricated on the same wafer. The divider operation is fully static, operating from f(clk) = 3 to 142.0 GHz while dissipating approximate to 800 mW of power in the circuit core. The circuit employs single-buffered emitter coupled logic (ECL) and inductive peaking. A microstrip wiring environment is employed for high interconnect density, and to minimize loss and impedance mismatch at frequencies > 100 GHz