An electrically driven exciton–polariton microlaser diode based on a ZnO:Ga microribbon heterojunction

Abstract

Unlike conventional photon lasing in the presence of population inversion, coherent light sources based on the exciton-polariton (EP) mode regime of light emission have attracted extensive attention recently because of their low-threshold or even threshold-free operation. Here, an electrically driven EP microlaser with distinguished multiple-mode structures and efficient suppression of spontaneous radiation background is represented. The device comprises of a Ga-doped ZnO (ZnO:Ga) microribbon assembled on a p-GaN substrate. The EP lasing behavior is clearly determined by the presence of superlinear power dependence, mode spacing broadening in the low-energy regime, larger mass of the lower polariton than that of classical photons, and especially the low threshold. In the laser device, the microribbon acts as an excellent laser gain medium and Fabry–Perot (F–P) optical resonator, providing a platform for the coupling between excitons and cavity photons, thus affording a huge Rabi splitting energy of 566 meV. By varying the cross-sectional sizes of microribbons, the electroluminescence characteristics can be significantly modulated. Of particular importance, the Rabi splitting energies can also be tuned ranging from 503–784 meV in the carefully constructed n-ZnO:Ga microribbon/p-GaN heterojunction devices. The high Rabi splitting energies are well above the thermal disturbance at room temperature, which contributes to achieving EP lasers. Therefore, this study provides a workable insight into the fabrication of room temperature low-threshold microlaser devices, which are electrically driven.