We use polarization-resolved two-photon microscopy to investigate second harmonic generation (SHG) from individual assemblies of site-controlled nano-pyramidal recess templates covered with silver films. We demonstrate the effect of the surface plasmon polaritons (SPPs) at fundamental and second-harmonic frequencies on the effective second order susceptibility tensor as a function of pyramid arrangement and inter-pyramid distance. These results open new perspectives for the application of SHG microscopy as a sensitive probe of coherently excited SPPs, as well as for the design of new plasmonic nanostructure assemblies with tailored nonlinear optical properties.

We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c‐axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 °C and 820 °C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p‐type GaN layers. With increasing misorientation, the free hole density drastically increases above 1018 cm–3. This improvement in p‐type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Rectangular arrays of pyramidal recesses coated by silver film are investigated by means of polarization-resolved nonlinear microscopy at 900 nm fundamental wavelength, demonstrating strong dependence of the dipole-allowed SHG upon the lattice parameters. The plasmonic band gap causes nearly complete SHG suppression in arrays of 650 nm periodicity, whereas a sharp resonance at 550 nm periodicity is observed due to excitation of band edge Bloch states at fundamental frequency, accompanied by symmetry-constrained interactions with similar modes at the second-harmonic frequency. Additionally, coupling with modes at the bottom side of the silver film may lead to extraordinary optical transmission, opening a channel for SHG from the highly nonlinear GaAs substrate. Changing the lattice geometry enables SHG intensity modulation over three orders of magnitude, while the effective nonlinear anisotropy can be continuously switched between the two lattice directions, reaching values as high as ±0.96.the entire "hyper-array", with parameters A and B in the 300-700 nm range. The arrays, each of size 10 × 10 μm, are separated by 10 μm gaps, which leads to a 20 μm overall pitch and a total size of the "hyper-array" of about 190 × 190 μm.

We fabricate and study quantum dot structures incorporating quasi-one-dimensional excited states. The structures are realized by graded bandgap GaAs/AlGaAs quantum wires self-formed inside inverted tetrahedral pyramids. The ground state transitions exhibit typical characteristics of fully confined excitons, including single photon emission. Efficient carrier thermalization and relaxation, as well as correlated photon emission is observed also among the excited states, indicating the formation of quasi-one-dimensional multi-exciton states. These structures offer interesting possibilities for collecting and directing charge carriers towards heterostructured potential traps.

Exciton recombination dynamics in tailored-potential, site-controlled AlGaAs quantum wires (QWRs) are studied. Time-resolved photoluminescence spectra evidence exciton localization in weakly disordered “uniform” QWRs, whereas deterministic bandgap grading is shown to suppress localization and promote exciton drift along the potential gradient. Measured exciton transit times between two quantum dot probes placed at opposite ends of the potential gradient yield the effective 1D exciton mobility as >1300 cm2/(eVs).