Efficient formation of excitons in a dense electron-hole plasma at room temperature

Commonly, excitons in semiconductors are regarded as a low-temperature, low carrier density phenomenon, becoming unstable as the temperature and carrier density increase. Contrary to the common expectation, our ultrafast conductivity and luminescence measurements in GaInN/GaN quantum wells reveal a highly efficient formation of radiative excitons from a high-density electron-hole plasma at room temperature, and provide a quantitative measure of the exciton fraction to reach more than 40% at a total carrier population as high as similar to 10(13) cm(-2). Driven by the mass action of electrons and holes, this effect is believed to contribute to the extraordinarily high quantum efficiency of group-III nitride light emitters.