Anisotropic lateral growth in GaAs MOCVD layers on (001) substrates

For metalorganic chemical vapor deposition, a fast lateral growth rate is observed for the first time on (001) GaAs having round mesas. The lateral growth rate is greater than the vertical growth rate by a factor of 3–5. The lateral growth rates have anisotropy with respect to the crystallographic directions on the (001) surfaces. The fastest growth direction is the [110] and the slowest one is the [10]. The [110] and [10] growth rates were found to be strongly dependent on growth conditions, though the vertical one is independent. The [110] growth rate decreases with decreasing As pressure, while the [10] remains constant. As growth temperature increases, both the [110] and the [10] growth rates decrease. A simple model for the lateral growth mechanism is proposed from the consideration of atomic arrangements and the number of dangling bonds at [110] and [10] step sites. According to the model, the lateral growth rate is proportional to the number of bonds available for binding Ga atoms at step sites. The model can explain well the anisotropy in the lateral growth rate and its dependence on the growth conditions.