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Fabrication of the fully hybrid bulk ZnO microcavity. (a) A single-crystal c-ZnO substrate is covered by a HfO2/SiO2 DBR (6.5 pairs) completed by Al. (b) The whole DBR/ZnO substrate is flipped upside-down and transferred to a glass substrate. (c) The ZnO substrate is backside etched/polished down to a thickness of several tens to hundreds nanometers. (d) A HfO2/SiO2 DBR (10 pairs) is deposited on top of the processed ZnO substrate. (e) High-angle annular dark field scanning transmission electron microscopy image of a SiO2/HfO2 Bragg reflector as used in the cavity. (f) 2 × 2 μm2 atomic force microscopy image of the completed cavity (root mean squared roughness: 9 Å). (g) Height profile along the dashed line shown in (f).
Quality factor measurement with pulsed excitation (frequency-tripled Ti:Al2O3 laser with a repetition rate of 76 MHz and pulses duration of 130 fs). (a) μPL spectrum measured at an angle of 0° and T = 300 K below the polariton lasing threshold. The cavity thickness is 2.5 λ. The width at half maximum of the emission line is 1.2 meV. The inset shows the Fourier space image of the emission at the same location. (b) μPL spectrum measured at an angle of −10° and T = 5 K on another point of the sample just above the polariton lasing threshold. The widths of the individual modes can be extracted and are as small as 0.8 meV, corresponding to Q values of up to 4000. The inset shows the Fourier space image of the polariton emission at the same location. The presence of a series of discrete individual modes is clearly visible.
Room-temperature polariton lasing. (a) Power dependent series of angle integrated μPL spectra measured at 300 K under quasi-continuous excitation (Nd:YAG laser with 4 kHz repetition rate and pulses of 400 ps, and a spot size of 2 μm). The excitation power relative to the threshold power is indicated for each spectrum. Inset: polariton lasing threshold at 300 K as a function of detuning. The arrow indicates the detuning at which the spectra in the main panels were obtained. Fourier space images (in linear scale) of the microcavity emission measured at 300 K and at the same point as in (a), under excitation power densities of 0.2Pth (b) and 1.2Pth (c), where Pth = 0.6 nJ/pulse is the polariton lasing threshold. At this point, the cavity optical thickness is 3λ, the Rabi splitting is 230 meV, and the detuning of the shown LPB is −8 meV.
Room temperature polariton lasing characteristics extracted from Fig. 3(a) . (a) Detailed view around 3.195 eV of the spectrum at 1.4Pth. For this power, and larger, two lasing modes, labelled by a square and by a circle symbols, can be resolved. (b) Integrated intensity, (c) linewidth, and (d) energy of the LPB/first lasing mode (square) and second lasing mode (circle), as a function of the excitation power.
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