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(a) Sketch of the V-groove QWR array (pitch and groove width equal to 1 μm and 300 nm, respectively). Below: zoom-in of the QWR region. (b)Cross-sectional AFM image of an InGaAsN QWR. The black area on top corresponds to the non-planarized remnant of the V-groove after MOCVD growth. (c) PL spectra of the investigated sample, before (bottom) and after (top) H irradiation. Spectra are normalized to the as-grown QWR peak; normalization factors are given. The peak visible in the high-energy region of the spectrum is due to the quantum well (QW) that forms on the planar part of the patterned substrate upon deposition of the QWR layer. For better visualization, the QW peaks were also normalized to the as-grown QWR emission.
Polar plot of the intensity of the quantum wire emission as a function of the angle θ between the polarization vector and the main QWR axis [labeled as x in the figure, see also Fig. 1(a)]. The shown datasets (normalized so that Ix + Iy = 1) are relative to the untreated (black-filled circles) and hydrogenated (red-filled squares) InGaAsN QWRs. The data displayed on the left- (right-) hand side were acquired at T = 10 K (180 K). The listed values of the degree of linear polarization (ρ) at T = 10 K and 180 K were obtained by fitting the formula (derived from Malus law) to the experimental data. The fitted curves are displayed as solid lines in the figure. Notice that θ = 2α, where α is the angle between the slow axis of the λ/2 retarder and the orientation of the linear polarizer (set parallel to x).
(a) and (b) PL spectra of the untreated (a) and hydrogenated (b) InGaAsN QWRs, recorded at different temperatures for polarization parallel (Ix ; thin, solid black line) and perpendicular (Iy ; thin, dashed black line) to the wire. The energy-dependent degree of linear polarization (ρ; thick, solid red line) is also shown. (c) and (d) Fitting procedure used to extract the value of the degree of polarization of the main QWR transition (ρ1 in the figure, whereas ρ2 is the polarization degree of the higher-energy peak). The T = 280 K data (solid line) are shown, together with their associated fit (dashed-dotted line). The curves relative to the polarization parallel (perpendicular) to the QWR are displayed in black (red). Two Gaussian peaks (displayed in the figure as dashed and dotted lines, respectively) are employed to fit the PL spectrum corresponding to each polarization. For the higher-energy transition, energy and linewidth of the Gaussian peak are kept constant for the two polarizations.
(a) Temperature dependence of the degree of linear polarization of the main QWR transition (the lower-energy peak in the spectra of Fig. 3), estimated from the fitting procedure outlined in Figs. 3(c) and 3(d). Data relative to the untreated (hydrogenated) InGaAsN QWR sample are reported as black-filled circles (red-filled squares). Solid lines are guides to the eye. (b),(c) Comparison between the maximum value (ρmax, black crosses) of the energy-dependent degree of linear polarization [see Figs. 3(a) and 3(b)] and the polarization degree of the lower- (ρ1, gray-filled circles) and higher-energy (ρ2, white-filled circles) QWR transitions, as estimated from the fitting procedure described in Figs. 3(c) and 3(d). For ρ2, only those datapoints for which the condition (where I 1 and I 2 are the intensities of the two QWR transitions) is respected are shown.
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