Characterization of defects in GaP and GaAsP graded heterojunctions by transmission electron microscopy

Misfit dislocations are observed in graded heterojunctions GaAs_1?xP_x by electron microscopy. Results are in agreement with previous work concerning the nature of the dislocations (Lomer and 60° dislocations) and their density dependence on the phosphorus gradient. The discussion concerns the formation of Lomer dislocations and the possibility of reducing the density of inclined dislocations which reach the surface of the epitaxial layer. GaP substrates, S-doped, are examined by transmission electron microscopy. Numerous defects such as Frank loops, perfect loops, helical dislocations and precipitates are observed. A GaP homoepitaxial layer realized on this substrate is free from these defects but exhibits stacking faults. A zinc diffusion does not produce additional defect but a 1000 Å thick amorphous layer is observed a at the surface.