NUCLEATION AND DEFECT GENERATION IN LATTICE MATCHED AND MISMATCHED HETEROEPITAXIAL LAYERS IN THE GAAS ALXGA1-XP/SI SYSTEM

The heteroepitaxial growth of GaAs on Si substrates at 700 °C using AlxGa1-xP buffer layers grown at 900 °C by metalorganic chemical vapor deposition is studied using transmission electron microscopy. This GaAs/AlxGa1-xP/Si system is unique in that it allows one to study separately the influence of lattice-mismatch (GaAs/AlxGa1-xP) and polar/nonpolar (AlxGa 1-xP/Si) effects on the heteroepitaxial growth of compound semiconductors. Island-type nucleation is observed for both effects acting independently, though three-dimensional growth due to the polar/nonpolar effect (AlxGa1-xP/Si) can be suppressed by increasing the Al content (x>0.2) of the AlxGa1-xP layers. The nucleation of the GaAs appears to be modified by the nature of the AlxGa 1-xP buffer layers, i.e., whether they are in the form of islands or planar layers. Single-crystal, 3-μm-thick layers of GaAs can be grown directly at 700 °C on the AlxGa1-xP buffer layers without resorting to a two-step technique. This result demonstrates that purely lattice-mismatch or polar/nonpolar effects cannot disrupt the crystallinity of the compound semiconductor layer. The surface morphology as well as the nature of defects generated in the 3-μm-thick GaAs films can be correlated to the nucleation mode of the GaAs.