The authors report the observation of electroluminescence from GaAs-based
semiconductor microcavities in the strong coupling regime. At low current
densities the emission consists of two peaks, which exhibit anti-crossing
behaviour as a function of detection angle and thus originate from polariton
states. With increasing carrier injection we observe a progressive transition
from strong to weak coupling due to screening of the exciton resonance by free
carriers. The demonstration that polariton emission can be excited by
electrical injection is encouraging for future development of polariton lasers.Comment: 13 pages, 3 figure