Bound states in optical absorption of semiconductor quantum wells containing a two-dimensional electron gas

The dependence of the optical absorption spectrum of a semiconductor quantu m well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fe rmi edge singularity at high n(e) The exciton peak (X) moves off to high en ergy, weakens, and disappears. The X,X- splitting is linear in n(e) and clo sely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn 0.002Te quantum wells in a magnetic field, the X,X- splitting reflects uneq ual Fermi energies for M = +/-1/2 electrons. The data are explained by Hawr ylak's theory of the many-body optical response including spin effects.