TRANSMISSION ELECTRON-MICROSCOPY AND CATHODOLUMINESCENCE OF TENSILE-STRAINED GAXIN1-XP INP HETEROSTRUCTURES .1. SPATIAL VARIATIONS OF THE TENSILE-STRESS RELAXATION/

We have investigated the optical and structural properties of tensile- strained GaxIn1-xP/InP heterojunctions by cathodoluminescence (CL) in the scanning electron microscope and by transmission electron microsco py (TEM). The lattice mismatch of the samples is ranging from 0.4% (x= 5.5%) to 0.84% (x=11.8%). We show, in agreement with previous studies, that the relaxation of tensile-strained epilayers occurs by the emiss ion of partial and perfect dislocations. The numerous twins and stacki ng faults which are found in the epilayers act as efficient recombinat ion centers for electron-hole pairs and appear as dark line defects (D LDs) in CL images. ''Ladderlike'' configurations of these defects are found both by TEM and CL in samples with a lattice mismatch larger tha n 0.5%. We also demonstrate that DLDs are contaminated by impurities. Areas with networks of perfect dislocations are found between the DLDs , The analysis of the dislocation types allows us to suggest that the growth of low-mismatched samples is two dimensional, and that it is th ree dimensional in highly mismatched samples. Finally, the spatial var iations of the strain relaxation throughout the samples are studied by 77-K CL spectroscopic measurements and it is shown that these variati ons can be correlated with the various types of structural defects. (C ) 1996 American Institute of Physics.