STEP-DENSITY DEPENDENCE OF GROWTH-RATE ON VICINAL SURFACE OF MOCVD

The dependence of the growth rate on the step density is reported for the first time. We accurately measured the growth rate on GaAs (001) vicinal substrates with various misorientation angles. The substrates were tilted toward the [110BAR] or [110] direction with the misorientation angle ranging from 1.0-degrees to 4.0-degrees. The growth rate was derived from the superlattice period of the (AlAs)1/2(GaAs)1/2 fractional layer superlattice (FLS) measured by X-ray diffraction satellite peaks. We obtained the step density dependence of the growth rate. The results reveal that on [110BAR] misoriented surfaces the growth rate decreases slightly with decreasing misorientation angle, i.e., with decreasing step density. The growth rate decreases by 5% as the misorientation angle decreases from 4.0-degrees to 1.0-degrees. On [110] misoriented surface with the same misorientation angle, the growth rates scatter, ranging about +/- 2% from run to run. These results for [110BAR] misoriented surfaces can be explained by a simple adsorption/desorption rate model, taking into account the rate for the group III atoms to desorb from the surface (1/tau(d)), as well as the rate for the group III atoms to hop to adjoining sites (1/tau(s)). As the misorientation angle decreases, the terrace width increases, and the mean time of migration of group III atoms to reach the site steps after adsorption at the surface increases. Therefore, the possibility of desorption increases, and the growth rate decreases slightly. A Monte Carlo simulation using this model fits the experimental results.