The nonlinear optical properties of a ͑InP͒ 2 /͑GaP͒ 2 bilayer superlattice structure have been examined with linearly polarized cathodoluminescence spectroscopy. Transmission electron microscopy showed a composition modulation with a period of ϳ800 Å along the ͓110͔ direction, which occurs spontaneously during the growth, resulting in coherently strained quantum wires. The strong excitation dependence of the polarization anisotropy and energy of excitonic luminescence from the quantum wires was found to be consistent with a band-filling model that is based on a k-p and two-dimensional quantum confinement calculation. ͓S0163-1829͑96͒51516-X͔ Nonlinear optical properties of III-V semiconductor nanostructures have attracted a great deal of interest, as they are important for applications in optical communications that involve switching, amplification, and signal processing. An important nonlinear optical property is the change in the emission of light ͑in energy, polarization, and intensity͒ that results from phase-space filling of carriers in one-and twodimensionally confined systems, i.e., quantum wells and wires. 1,2 This property is analogous to the Burstein-Moss band filling which occurs in bulk semiconductors and raises the energy of the unoccupied electron and hole states as the excitation intensity increases. As the dimensionality of the quantum confinement increases from one dimension ͑1D͒ to 2D, the narrowing of the density of states ͑DOS͒ will exhibit a lower excitation threshold for phase-space filling, thereby yielding potentially enhanced nonlinear optical effects. Recently, quantum wires have been fabricated by a straininduced lateral ordering ͑SILO͒ process which occurs spontaneously when (GaP) n /(InP) n and (GaAs) n /(InAs) n shortperiod superlattices are grown on GaAs͑001͒ and InP͑001͒, respectively. 3-7 Previous studies involving transmission electron microscopy ͑TEM͒ and optical measurements such as photoluminescence, electroluminescence, and photoreflectance have shown evidence supporting the existence of quantum wires due to quantum confinement along both the growth direction and the composition modulation direction. 5-8 However, the nature of phase-space filling and the concomitant influence on the polarization properties in these systems have yet to be investigated thoroughly. In this study, we examine the nonlinear optical properties of a ͑InP͒ 2 /͑GaP͒ 2 bilayer superlattice ͑BSL͒ structure using a linearly polarized cathodoluminescence ͑LPCL͒ technique. We demonstrate the existence of an interesting excitation-and temperature-dependent polarization anisotropy in luminescence coming from the SILO quantum wires. A theoretical simulation of the band-filling, luminescence energy shifts and polarization anisotropy changes was performed for the SILO quantum wires using a k-p band-structure calculation, which takes the coherency strain and 2D quantum confine-ment into account, and is compared with the experimental results. Evidence for these strong nonlinear optical effects is a cornerstone in ...

Thermally annealed GaN nucleation layers and the devicequality metal organic chemical vapor deposition growth of Sidoped GaN films on (00.1) sapphire

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Recent advances in Spectrolab's high efficiency III-V multi-junction space solar cells are reported. The latest generation GaInP/GaAs/Ge solar cells under production-the Ultra Triple Junction (UTJ)-have an average efficiency at maximum power of 28Á0% (AM0, 28 C, 135Á3 mW/cm 2 ) at beginning of life (BOL), and 22Á6% at 60 C at end of life (EOL, 15 years in GEO orbit). This represents a 5Á5% relative higher efficiency at EOL, compared with the previous generation Improved Triple Junction (ITJ) cells. The P/P 0 -for 1 MeV electrons after 10 15 cm À2 fluence has also improved to 0Á86, compared with 0Á84 for the ITJ cells. These and other performance results of UTJ solar cells are reviewed in comparison with ITJ solar cells.

The effect of the heterojunction interface on the performance of high bandgap InxGa1−xP:Te/Al0.6Ga0.4As:C tunnel junctions (TJs) was investigated. The insertion of 30 Å of GaAs:Te at the junction interface resulted in a peak current of 1000 A/cm2 and a voltage drop of ∼3 mV for 30 A/cm2 (2000× concentration). The presence of this GaAs interfacial layer also improved the uniformity across the wafer. Modeling results are consistent with experimental data and were used to explain the observed enhancement in TJ performance. This architecture could be used within multijunction solar cells to extend the range of usable solar concentration with minimal voltage drop.

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