EXTRINSIC EFFECTS IN REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION PATTERNS FROM MBE GAAS

One uncontrolled parameter of MBE growth on GaAs is the orientation of the substrate. Typical material is oriented to within one-half degree of a low-index bulk plane so that the resulting surface consists of a staircase with random terrace lengths and step heights. These steps are important since at room temperature they can orient epitaxial layers and a high temperatures the terrace lengths can be comparable to diffusion distances. Ordered step arrays can also be an important factor in the formation of the characteristic streaked RHEED pattern. The authors have measured the profiles of these streaks from different wafers with nominally GaAs(001) surfaces and have observed striking differences which they ascribe to ordered staircase steps due to crystal misorientation. Misorientations as small as 1 mrad have been found. Surfaces in which the misorientation from the (001) was about 6. 5 mrad were studied extensively and a reciprocal lattice was constructed from a map of the diffracted intensity vs scattering angles. On surfaces misoriented by 1 degree , RHEED oscillations were found to be much weaker than on the 6. 5 mrad surface.