  We report on the study of many-body interactions in a single high quality
V-shaped quantum wire by means of continuous and time-resolved
microphotoluminescence. The transition from a weakly interacting exciton gas
when the carrier density n is less than 10^5 cm^-1 (i.e. n aX < 0.1, with aX
the exciton Bohr radius), to a dense electron-hole plasma (n > 10^6 cm^-1, i.e.
n aX > 1) is systematically followed in the system as the carrier density is
increased. We show that this transition occurs gradually : the free carriers
first coexist with excitons for n aX > 0.1, then the electron-hole plasma
becomes degenerate at n aX = 0.8. We also show that the non-linear effects are
strongly related to the kind of disorder and localization properties in the
structure especially in the low density regime.
