Influence of surface steps on N incorporation in GaAsN grown by chemical beam epitaxy

GaAsN epitaxial thin films were grown on GaAs (001) substrate by chemical beam epitaxy (CBE) with dimethylhydrazine ((CH₃)₂N ₂H₂, DMHy) as the N source that decomposes at a low temperature. We investigated the influences of the gas flow ratio of DMHy to the group V sources ([DMHy]/V), and surface steps on the N composition in GaAsN thin films. At the growth temperature of 420 °C, the N composition increased with increasing [DMHy]/V, indicating the N composition is determined by the amount of N supplied to the growing surface. In addition, the N composition also increased with increasing surface step density on GaAs (001) substrate orientated towards [010] from 0 to 10°. However, when the density of surface step is low (0-3 × 10² μm^-1), the dependence of N composition on surface step density cannot be explained by only the N incorporation at the surface steps on the GaAs substrate. In this case, the surface morphology thought to be rough, since it suggest that N atoms are incorporated at the steps around the nuclei on the growing surface. On the contrary, when the density of surface step is high (3-7 × 10² μm^-1), the N incorporation occurs at the steps as they move forward, resulting in the flat surface morphology. It was confirmed by the surface morphology observation of the samples grown on 2 and 10° off substrates, and the root-mean-squares of surface roughness were 1.1 and 0.3nm, respectively. These results indicate the surface morphology of the GaAsN thin films is affected strongly by the step density.