Room Temperature Electrically Injected Polariton Laser

Room temperature electrically pumped inversionless polariton lasing is observed from a bulk GaN-based microcavity diode. The low nonlinear threshold for polariton lasing occurs at $169\mathrm{A}/{\mathrm{cm}}^2$ in the light-current characteristics, accompanied by a collapse of the emission linewidth and small blueshift of the emission peak. Measurement of angle-resolved luminescence, polariton condensation and occupation in momentum space, and output spatial coherence and polarization have also been made. A second threshold, due to conventional photon lasing, is observed at an injection of $44\mathrm{kA}/{\mathrm{cm}}^2$.

Figure 1

(a) Schematic representation of the GaN microcavity diode. The inset shows a scanning electron microscopy image of the ${\mathrm{SiO}}_2/{\mathrm{TiO}}_2$ DBR mirror on one side, (b) scanning electron microscopy image of the fabricated device, (c) angle resolved electroluminescence spectra measured at room temperature, (d) calculated polariton dispersion from a coupled harmonic oscillator model alongside the measured data of (c).

Figure 2

Polariton and photon lasing characteristics at normal detection angle. (a) Integrated EL intensity, LP emission linewidth, and blueshift of peak emission as a function of injected current density. The solid lines are guides to the eye and the dashed green line shows the calculated intensities, (b) EL spectra measured at various injection levels. Inset shows the spectra above threshold (5 mA), (c) light-current characteristics of photon lasing observed in the same device at higher injection levels. Inset shows EL spectra measured above photon lasing threshold (1.04 A), (d) two threshold lasing behavior with the nonlinearities due to polariton and photon lasing.

Figure 3

(a)–(c) False color plots of energy-momentum distribution of polaritons at different current injection densities obtained from angle resolved EL measurements. (d) LP ground state occupancy for different $k_{\parallel }$ states obtained from angle-resolved data.

Figure 4

Spatial distribution and coherence of polariton condensates above threshold showing (a) multiple condensate droplets, (b) enlarged image (by 3.3 times) of a single condensate identified by the arrow, (c) variation of condensate size with injection level, and (d) interference visibility measured as a function of the displacement between a double image of the polariton emission below and above threshold current. Inset shows interference pattern for $x=1\mu \mathrm{m}$.