Bound States in Optical Absorption of Semiconductor Quantum Wells Containing a Two-Dimensional Electron Gas

Abstract

The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration ${n}_{e}$ is studied using CdTe samples. The trion peak $({X}^{\ensuremath{-}})$ seen at low ${n}_{e}$ evolves smoothly into the Fermi edge singularity at high ${n}_{e}$. The exciton peak $(X)$ moves off to high energy, weakens, and disappears. The ${X,X}^{\ensuremath{-}}$ splitting is linear in ${n}_{e}$ and closely equal to the Fermi energy plus the trion binding energy. For ${\mathrm{Cd}}_{0.998}{\mathrm{Mn}}_{0.002}\mathrm{Te}$ quantum wells in a magnetic field, the ${X,X}^{\ensuremath{-}}$ splitting reflects unequal Fermi energies for $M\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}1/2$ electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects.