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Sample schematic. (a) and (b) display a schematic of a sample and a scanning electron micrograph, respectively. A sample contains several hundred resonators on a area and Ge/Au ohmic contacts on two opposing sides of the sample for electrical contact. A zoom into the structure illustrates mode confinement in the cavity with an electric field oriented to couple well to the intersubband transitions. This behavior is confirmed by a finite element simulation shown in (d), where the arrows display electrical field orientation (arrow direction) and magnitude (arrow size). The cavities are filled with eight parabolic quantum wells (c). Their modulation doping is indicated by the red lines.
Normalized electroluminescence spectra with different cavity resonance frequencies at cryogenic (a) and room (b) temperature as lines. Spectra are offset by one scale unit from each other. Simulated empty cavity modes are displayed as triangles. At cryogenic temperatures, the spectra show two distinct peaks corresponding to the two polariton states. The driving currents were 80–100 mA for the different spectra. The peaks shift with cavity resonance and a clear anticrossing is observed. Close to the anticrossing point (third spectrum from the bottom), the quality factors and magnitudes of the peaks are very similar, owing to the mixed light matter character of the states. (b) At room temperature, the Rabi frequency of does not change, but the emitted power drops. Two-Lorentzian fitting curves for extraction of the two polariton peaks are plotted as dashed lines. Local maxima within the width of the broad higher energy upper polariton branch are disregarded as noise. The drive current was 50–60 mA for the different spectra. All resonators have a capacitance diameter of. The inductance lengths are (from bottom to top) . Bold values indicate samples also presented at room temperature. Noise levels for the spectra are indicated as grey bars.
Position of the emission peaks at cryogenic temperature (blue dots) and room temperature (red squares), along with the predictions of a theoretical model (continuous lines). Peak positions at room temperature are picked by fitting a double Lorentzian to the spectrum. The errors are typically below the size of the symbols. Both data sets agree well with the model and reproduce a polaritonic gap of 260 GHz.
Emission power of the polariton devices is compared to grating emitters. Dots correspond to polaritonic devices, while squares represent grating emitters. For both device types, black/blue/green/magenta/red represents temperatures of 10 K/50 K/100 K/150 K/300 K. To ensure the emission is of polaritonic origin, a spectrum was measured at each data point. The polaritonic device outperforms the grating emitter by a factor of 2.7 at low temperatures. This factor increases to above 10 at T = 100 K. At temperatures above 100 K, there was no peak visible any more for the grating devices, while the polaritonic emitter still operates up to room temperature.
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