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 quantum well on two-dimensional electron concentration nₑ is studied using CdTe samples. The trion peak (X^-) seen at low nₑ evolves smoothly into the Fermi edge singularity at high nₑ. The exciton peak $(X)$ moves off to high energy, weakens, and disappears. The X,X^- splitting is linear in nₑ and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X^- splitting reflects unequal Fermi energies for M0ex0ex=0ex0ex±1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects.