Characterization of the MBE growth of GaAs/Si(100) as a function of epilayer thickness

Abstract

GaAs has been grown by MBE on Si(100) substrates using the two-step process, where a low temperature, slow growth rate buffer layer is deposited before the growth of the active layer. For a series of such samples, the total epitaxial layer thickness was varied in the range 1.1 ⩽ Θ ⩽ 8.1 μm. Investigations using double-crystal X-ray diffraction confirmed that the structural quality of the GaAs improved with thickness. The Hall effect, however, showed that the electrical properties of the epilayer improved up to ⋍ 4.1 μm, but beyond this thickness the measured mobilities decreased. By employing the defect revealing Wright etch it was observed that for Θ > 4 μm cracks begin to form within the epilayer, resulting from the mismatch between substrate and epilayer thermal expansion coefficients. It therefore seems that Hall measurements are not meaningful in the presence of these thermal cracks, and so an upper thickness limit of ≈- 4 μm is placed on such characterization.