  We study the magneto-transport and magneto-electroluminescence properties of
purely n-doped GaAs/Al$_{0.6}$Ga$_{0.4}$As resonant tunneling diodes with an
In$_{0.15}$Ga$_{0.85}$As quantum well and emitter prewell. Before the resonant
current condition, magneto-transport measurements reveal charge carrier
densities comparable for diodes with and without the emitter prewell. The
Landau level splitting is observed in the electroluminescence emission from the
emitter prewell, enabling the determination of the charge carrier build-up. Our
findings show that magneto-electroluminescence spectroscopy techniques provide
useful insights on the charge carrier dynamics in resonant tunneling diodes and
is a versatile tool to complement magneto-transport techniques. This approach
will drive the way for developing potentially more efficient opto-electronic
resonant tunneling devices, by e.g., monitoring voltage dependent charge
accumulation for improving built-in fields and hence to maximize photodetector
efficiency and/or minimize optical losses.
