Modulation-doped GaAs quantum wires are grown on the surfaces with giant st
eps which are naturally formed on vicinal GaAs (110) substrates by molecula
r beam epitaxy (MBE). It is found that photoluminescence (PL) peaks shift t
o lower energy with increasing doping level and to higher energy with incre
asing excitation intensity. These results indicate that the GaAs quantum wi
res are successfully modulation-doped.