We have used Optically Detected Resonance (ODR) spectroscopy to probe the e
lectronic properties of undoped and barrier-doped GaAs/Al0.3Ga0.7As multipl
e-quantum-well (MQW) samples with well widths between 12.5 and 20 nm in mag
netic fields up to 15 T at low temperatures. The simultaneous observation o
f electron and hole CR along with several internal transitions of neutral e
xcitons (IETs) verifies the symmetry-related energy differences of the inte
rnal transitions to differences between electron and hole CR. The observed
degeneracy of the 1s --> 2p(+) IET from the two radiative magneto-excitons
is due to the very small electron g-factor. ODR measurements on 20 nm wide
MQWs (not-intentionally- and barrier-doped) exhibit transitions of the nega
tively charged excitonic complex.