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A tectonic window into the upper 2,000 m of oceanic crust generated at the superfast spreading (∼142 mm/yr) southern East Pacific Rise exposes a continuous layered structure of basaltic lavas and sheeted dikes over gabbroic rocks. This relatively simple structure is in accord with expectations for crustal accretion at a very fast spreading rate and high magma budget where magmatic construction keeps pace with plate separation. Detailed observations show that basaltic lava flows dip progressively more steeply inward (toward the spreading axis where they were erupted). Underlying sheeted dikes are faulted and tectonically rotated to dip steeply outward. These structures are interpreted in terms of subsidence beneath the axis of the southern East Pacific Rise during crustal construction that allowed the lava unit to thicken to >400 m without creating comparable relief at the spreading center. Transitional units above and below the sheeted dike complex show that the thickness of upper crustal rock units is modified by tectonic and intrusive processes during accretion. The crustal structure shows that even approaching the superfast spreading end‐member of seafloor spreading, crustal accretion involves dramatic tectonic processes that are not obvious from the surface geology of spreading centers. Plain Language Summary: Studies of mid‐ocean ridge spreading centers document the surface expression of spreading axes where new oceanic crust is constructed. Where major fault scarps cut into the oceanic crust, the structure and composition of that crust can be viewed in the third dimension. The Pito Deep Rift (PDR) in the SE Pacific exposes the upper 2,000 m of the oceanic crust that was created by seafloor spreading at the southern East Pacific Rise at a rate of >140 mm/yr, one of the fastest spreading parts of the global Mid‐Ocean Ridge system. The geologic structure of lava flows, dikes that feed them, and magma‐chamber rocks shows how these units were assembled beneath the spreading center. At high spreading rates, new oceanic crust is thought to be constructed mainly by the eruption of lava flows and the intrusion of dikes above a magma chamber, with little faulting. The pattern of tilting and fracturing of lava flows and dikes at the PDR shows that even at a very high spreading rate, building the upper crust is more complicated than suggested by surface studies alone. Key Points: Upper oceanic crust of the superfast‐spreading southern East Pacific Rise is exposed along escarpments at the Pito Deep Rift (SE Pacific)The upper crustal units include continuous layers of lavas, sheeted dikes, gabbroic rocks, and transitional unitsTilted and fractured lava flows and dikes show that subaxial subsidence and brittle deformation occurred during superfast crustal accretion [ABSTRACT FROM AUTHOR]

Author(s): P. Gaal [1]; W. Kuehn [1]; K. Reimann [1]; M. Woerner (corresponding author) [1]; T. Elsaesser [1]; R. Hey [2] A charged particle modifies the structure of the surrounding [...]

The negative differential conductivity and laser level population in undoped GaAs/(Al,Ga)As quantum-cascade structures using current-voltage characteristics and interband photoluminescence spectroscopy is investigated. A unidentified state which exhibits a strong photoluminescence signal may play a role in the bistability.

The proposed analytical approach provides a simple tool for the determination of the waveguide losses for any quantum-cascade laser without adopting a numerical solver in addition to achieving a direct physical insight into the influence of free-carrier absorption on the laser performance. The influence of the free-carrier absorption in the cascade itself can be neglected except for very high injector doping densities.

Research describing deformation fields in epitaxial layer stacks is presented. Comparisons are studied by crystal diffractometry of wafer bonding to various different templates.

The influence of localization and exciton diffusion on cathodoluminescence (CL) intensity distribution in multiple and single quantum well structures is determined using scanning electron microscopic methods. The quantum well structures are prepared by the technique of growth interrupted molecular beam epitaxy. The diffusion of excitons into the quantum well regions is directly proportional to the spatial and spectral CL intensity distribution.

The characteristics of GaAS/AlAs multilayer systems were investigated using double crystal topography and diffractometry to determine their suitability for applications in optical Bragg reflectors. The results showed that misfit dislocation formation was inhibited by higher silicon doping levels. In the case of Czochralski substrates, misfit dislocations between pairs of threading dislocations produced half loops.

With strong THz pulses, we measure ultrafast transport of electrons, holes, and an electron-hole plasma in GaAs. The transition from ballistic to drift-like transport is strongly influenced by electron-hole scattering.