  A configuration space approach is developed to uncover generic stability
peculiarities for the lowest energy neutral and charged exciton complexes
(biexciton and trion) in quasi-one-dimensional semiconductors. Trions are shown
to be more stable than biexcitons in strongly confined structures with small
reduced electron-hole masses. Biexcitons are more stable in less confined
structures with large reduced electron-hole masses. In semiconducting carbon
nanotubes, in particular, the trion binding energy is shown to be greater than
that of the biexciton by a factor ~1.4 decreasing with diameter, thus revealing
the general physical principles that underlie recent experimental observations.
