Figures

Figure 1

Typical microcavity structures. The central cavity layer having a thickness equal to an integer number of half-wave-lengths of light at the exciton resonance frequency is sandwiched between two Bragg mirrors. A quantum well (a), or several quantum wells (b) are embedded at the antinodes of the cavity mode electric field in order to provide the strongest coupling to light.

Figure 2

Reflection spectra of a GaN-based microcavity calculated for different detunings between the cavity mode and the exciton resonance. One can clearly show the anti-crossing of the polariton eigen states.

Figure 3

Energy versus in-plane wave vector for the exciton-polariton modes in a GaN-based microcavity similar to the one described in ref [68] for the cases of positive (a), zero (b), and negative (c) detuning between the cavity photon mode frequency and the exciton resonance.

Figure 4

Electric field of a light-wave penetrating into a typical Bragg mirror. Refractive indices of its quarter-wave layers are nA=1.6, nB=2.6.

Figure 5

Dashed line : Dispersion relation of uncoupled photons and excitons in a semi-infinite semiconductor. Solid line : Dispersion relation of bulk exciton-polaritons in the regime of strong exciton-light coupling. One can see that there is no lower branch ground state.

Figure 6

a) Dashed line : Dispersion relation of uncoupled photons and excitons in a GaAs microcavity. Solid line : Dispersion relation of microcavity polaritons in the strong-coupling regime in a typical GaAs-based cavity. b) Dispersion relation of polaritons in a model GaN-based microcavity. The arrows sketch exciton relaxation paths trough their interaction with acoustic phonon and their blocking in the bottleneck region. c) Scheme of the experiment performed in [5]. A short pumping laser pulse creates a polariton population at the inflexion point of the lower polariton branch dispersion. A probe pulse illuminates the cavity under normal incidence within a short delay with respect to the pump. It seeds the ground polariton state, stimulating the resonant polariton-polariton scattering.

Figure 7

Phase diagrams for GaAs (a), CdTe (b), GaN (c), and ZnO (d) based microcavities. Vertical and horizontal dashed lines show the limits of the strong-coupling regime imposed by the exciton thermal broadening and screening, respectively. Solid lines show the critical concentration Nc versus temperature of the polariton KT phase transition. Dotted and dashed lines show the critical concentration Nc for quasi condensation in 100 µm and 1 meter lateral size systems, respectively. The thin dotted line symbolizes the limit between vertical cavity surface emitting laser (VCSEL) and light-emitting diode regimes.

Figure 8

Distribution function of polaritons at 10 K when non-resonantly pumped with a power of 4.2 W/cm2. Results are shown for (a) polariton-acoustic phonon scattering (dotted), (b) as (a) plus polariton-polariton scattering (dashed) , and (c) as (b) plus polariton-electron scattering (solid). The thin dotted line shows the equilibrium Bose distribution function with zero chemical potential.

Figure 9

Polariton occupation of the k=0 state vs time for (a) excitation powers of 0.42 W/cm2 (dashed), 4.2 W/cm2 (dotted), 168 W/cm2 (solid). The pump is turned on at t=0. The corresponding total polariton equilibrium densities are 7.0x1010 cm-2, 1.3x109 cm-2 and 1.3x1010 cm-2. (b) As (a) for a pump power of 0.42 W/cm2 and electron doping of 2.5 x109 cm-2 (dashed), 1010 (dotted), 4x1010 cm-2 (solid).

Figure 10

Radiative efficiency vs power absorbed in the microcavity at 10 K, for (a) a doped cavity, ne=1010 cm-2, (b) an undoped cavity, and (c) as (a) but including the effects of electron gas heating. The dotted part of the curve (b) corresponds to a calculated exciton density >5x1010 cm-2.

Figure 11

Schematic proposed GaN-based polariton laser.

Figure 12

Solid lines: exciton-polariton kinetic distribution functions of the GaN microcavity under non-resonant cw optical pumping at 300 K. The pump power densities used are (a) 1000 W/cm2 and (b) 40000 W/cm2. Black points and open circles show the values of the distribution function for the lowest energy states (assuming the exciting light spot is 50 µm radius) for pump densities of 1000 W/cm2 and 40000 W/cm2, respectively. Dashed line shows the Bose-Einstein polariton distribution function of the same microcaity assuming a vanishing chemical potential. Inset shows the radiative efficiency of the polariton laser versus the pumping power density at 300 K.

© 2003 The Materials Research Society