  We explore the properties of high-redshift Lyman-alpha emitters (LAE), and
their link with the Lyman-Break galaxy population (LBG), using a semi-analytic
model of galaxy formation that takes into account resonant scattering of Lya
photons in gas outflows. We can reasonably reproduce the abundances of LAEs and
LBGs from redshift 3 to 7, as well as most UV LFs of LAEs. The stronger dust
attenuation for (resonant) Lya photons compared to UV continuum photons in
bright LBGs provides a natural interpretation to the increase of the LAE
fraction in LBG samples, X_LAE, towards fainter magnitudes. The redshift
evolution of X_LAE seems however very sensitive to UV magnitudes limits and EW
cuts. In spite of the apparent good match between the statistical properties
predicted by the model and the observations, we find that the tail of the Lya
equivalent width distribution (EW > 100 A) cannot be explained by our model,
and we need to invoke additional mechanisms. We find that LAEs and LBGs span a
very similar dynamical range, but bright LAEs are about 4 times rarer than LBGs
in massive halos. Moreover, massive halos mainly contain weak LAEs in our
model, which might introduce a bias towards low-mass halos in surveys which
select sources with high EW cuts. Overall, our results are consistent with the
idea that LAEs and LBGs make a very similar galaxy population. Their apparent
differences seem mainly due to EW selections, UV detection limits, and a
decreasing Lya-to-UV escape fraction ratio in high SFR galaxies.
