Linear Polarization Dependence Research Articles

Comparison of atomic structure anisotropy between Co-Pd alloys and Co/Pd multilayer films

We have employed Co K-edge extended x-ray absorption fine structure measurements with linear polarization dependence to investigate the chemical short-range order (SRO) and interatomic distance anisotropy in ${\mathrm{Co}}_{X}{\mathrm{Pd}}_{1\ensuremath{-}X}$ alloy $(X=0.16,0.31)$ and $[\mathrm{Co}(2 \AA{})/\mathrm{Pd}(Y \AA{}){]}_{13}$ multilayer films $(Y=15,$ 32). The SRO parameters of in-plane first nearest neighbors, 0.063--0.068 in the alloys and 0.012--0.036 in the multilayers, are observed. Surprisingly, these counterintuitive results show clear evidence that the Co atoms at the Co/Pd interfaces in multilayers have more alloylike characteristic than those in alloys with respect to local chemical environment.

Polarization effects in AlGaAs single quantum well laser structure

The linear polarization dependence of the photoluminescence of Al 0.08Ga 0.92As single quantum well laser structure has been investigated for the incident light propagating parallel to the plane of the structure. The polarization dependent excitonic recombinations exhibit fully polarized behavior of heavy- and light-holes for in plane incident electric field vector. The rotation of excitation beam polarization by 90°, however, shows depolarized behavior of excitonic recombinations. The strain induced mixing of heavy- and light-hole valence band is also inferred in this excitation geometry.

Clear evidence for strain changes according to Co layer thickness in metastable Co/Pd(111) multilayers: An extended x-ray absorption fine structure study.

We have measured fluorescence-yield extended x-ray absorption fine structure (EXAFS) on a series of (Co x \AA{}+Pd 11 \AA{}${)}_{13}$ metallic multilayers. To examine the local atomic structure around Co and its anisotropy, Co K-edge EXAFS measurements were performed at near-grazing incidence of synchrotron radiation incorporating linear polarization dependence. We generally observed, with decreasing Co layer thickness, increasing, in-plane interatomic distance and decreasing, out-of-plane interatomic distance in Co atoms. For a (Co 10 \AA{} +Pd 11 \AA{}${)}_{13}$ multilayer, strain values of in-plane and out-of-plane Co atoms are estimated to be 3.6\ifmmode\pm\else\textpm\fi{}0.5% in tensile and 3.0\ifmmode\pm\else\textpm\fi{}0.4% in compressive strain. \textcopyright{} 1996 The American Physical Society.

Optical properties of quantum-wire arrays in (Al,Ga)As serpentine-superlattice structures.

Serpentine superlattices with a built-in quantum-wire array have been grown on vicinal (100) GaAs substrates by molecular-beam epitaxy. The quantum wires have parabolic cross sections with confinement dimensions on the order of 100 \AA{}. The goal of this paper is to make a comprehensive optical study of two different serpentine-superlattice samples. The serpentine structures have been characterized by low-temperature cathodoluminescence, photoluminescence, and photoluminescence-excitation measurements. In photoluminescence, a rather sharp peak (typically 7 meV full width at half maximum) is attributed to excitonic recombination in the built-in quantum-wire array. The linear polarization dependence of the serpentine-superlattice emission has been measured with a photoelastic modulation technique, showing a pronounced polarization anisotropy in both photoluminescence and photoluminescence excitation. The serpentine-superlattice photoluminescence emission normal to the vicinal surface shows a linear polarization along the wires of up to about 30% due to the lateral confinement. The carrier confinement has been further characterized by measuring the linear polarization dependence of the photoluminescence normal to the cleaved edges. The measured polarization anisotropy has been compared with the calculated polarization dependence as a function of intermixing between the lateral barriers and wells. It is found that there is a substantial intermixing between the barriers and wells, with at least 30% of the Al intended for the barrier ending up in the well.This results in hole states confined to one dimension, while the electron states are two dimensional due to coupling through the lateral barriers. Linearly polarized photoluminescence excitation has been used to reveal the laterally induced heavy-hole--light-hole splitting. Photoluminescence decay-time measurements of the serpentine-superlattice emission (390 ps) show a longer radiative decay time at low temperature than for a reference alloy-well structure (260 ps), indicating a reduced recombination rate in the serpentine structure. The linear polarization of the photoluminescence is found to be rather constant over large areas of the wafer even though the growth rate varies by a few percent. This indicates that uniform quantum-wire-like states are formed and demonstrates the intended advantage of the serpentine superlattice, which avoids the tilt sensitivity of the tilted superlattice.

InGaAs quantum well wires grown on patterned GaAs substrates

Strained InGaAs/GaAs quantum well wires have been grown on 2300 Å period gratings etched into GaAs substrates. Both conventional molecular beam epitaxy and migration-enhanced epitaxy have been used as growth techniques. The low-temperature photoluminescence from the quantum well wires was compared to the photoluminescence from a planar quantum well sample grown simultaneously. The planar samples showed a sharp single peak, whereas the patterned samples displayed two peaks. The samples grown by conventional molecular-beam epitaxy had two fairly broad, overlapping peaks of comparable intensity. The samples grown by migration-enhanced epitaxy had two distinct peaks, with one peak an order of magnitude larger than the other. Polarization-dependent photoluminescence was performed on the migration-enhanced epitaxy grown samples. The larger of the two peaks on the patterned sample showed a 21% linear polarization dependence, while the other peak showed unpolarized emission. In addition, the quantum well grown on the unpatterned substrate exhibited unpolarized emission.

Linear polarization effects in anisotropic photoemission from GaAs/AlAs short-period superlattices

By investigating the linear polarization dependence of intrinsic emissions from undoped GaAs/AlAs short-period superlattices at room temperature, it is shown that a dominating peak observed in the normal emission spectra is due to the free-carrier recombination associated with the lowest electron to mixed-hole subbands with an unexpectedly large light-hole character instead of with the lowest electron to pure heavy-hole subbands expected in an ideal superlattice. Origins of the extensive valence-band mixing in the synthesized superlattices are discussed in relation to microscopic fluctuations in the layer thicknesses observed in the transmission electron microscope lattice image.