  Slow or even stop electromagnetic (EM) waves attract researchers' attentions
for its potential applications in energy storage, optical buffer and
nonlinearity enhancement. However, in most cases of the EM waves trapping, the
EM waves are not truly trapped due to the existence of reflection. In this
paper, a novel metal-semiconductor-semiconductor-metal (MSSM) structure, and a
novel truly rainbow trapping in a tapered MSSM model at terahertz frequencies
are demonstrated by theoretical analysis and numerical simulations. More
importantly, functional devices such as optical buffer, optical switch and
optical filter are achieved in our designed MSSM structure based on truly
rainbow trapping theory. Owing to the property of one-way propagation, these
new types of optical devices can be high-performance and are expected to be
used in integrated optical circuits.
