Crystal quality of GaAsN films can be improved by using CBE for low-temperature growth. However, low-temperature growth increases C incorporation in the films, which degrades their electrical properties. Consequently, C incorporation was investigated in view of the surface reaction of N sources on a substrate surface, and MMHy and DMHy were compared. When MMHy was used as an N source, C concentration in GaAsN drastically increases below 380 degrees C than that in GaAs due to insufficient CH, desorption. In the case of DMHy, N(CH3)(2) is desorbed more readily than CHx, therefore, the C concentration can then be reduced using DMHy. (c) 2006 Elsevier B.V All rights reserved.