  Accurate modeling of charge transport and both thermal and luminescent
radiation is crucial to the understanding and design of radiative thermal
energy converters. Charge carrier dynamics in semiconductors are well-described
by the Poisson-drift-diffusion equations, and thermal radiation in
emitter/absorber structures can be computed using multilayer fluctuational
electrodynamics. These two types of energy flows interact through radiation
absorption/luminescence and charge carrier generation/recombination. However,
past research has typically only assumed limited interaction, with thermal
radiation absorption as an input for charge carrier models to predict device
performance. To examine this assumption, we develop a fully-coupled iterative
model of charge and radiation transport in semiconductor devices, and we use
our model to analyze near-field and far-field GaSb thermophotovoltaic and
thermoradiative systems. By comparing our results to past methods that do not
consider cross-influences between charge and radiation transport, we find that
a fully-coupled approach is necessary to accurately model photon recycling and
near-field enhancement of external luminescence. Because these effects can
substantially alter device performance, our modeling approach can aid in the
design of efficient thermophotovoltaic and thermoradiative systems.
