It is shown that GaN layers can be grown on (100)- and (111)- oriented poro
us single-crystal GaAs substrates by molecular-beam epitaxy with plasma act
ivation of the nitrogen by an rf electron cyclotron resonance discharge. Th
e resulting undoped epitaxial layers possessed n-type conductivity with a c
arrier concentration similar to 10(18). Data obtained by scanning electron
microscopy and cathodoluminescence indicate that at thicknesses similar to
2000 Angstrom, continuous layers of the cubic GaN modification are obtained
regardless of the substrate orientation. (C) 1999 American Institute of Ph
ysics. [S1063-7850(99)00101- 9].