Electron Microscope Studies Of Vpe Gainas Layer Structures Suitable For Use As Infrared Leds

Abstract

SUMMARYElectron microscope investigations have been carried out on vapour grown (100) GaAs/GaInAs structures designed for use as infrared emitters of wavelength 1·06 μm. The structures consist of a GaAs substrate, a graded layer in which the indium concentration is increased from zero to 17 atomic %, and a constant composition Ga0·83In0·17As layer which contains a p‐n junction. X‐ray microprobe analysis of cross‐sections of the slices established the uniformity of the grading. TEM analysis showed a dense and extensive asymmetric network of misfit dislocations (1 × 1012 m−2 (108 cm−2)) in the graded layer, threading dislocations and other anomalous contrast features extending from the graded layer through the p‐n junction to the surface (local densities of 1 × 1011–1 × 1012 m−2 (107–108 cm−2)), and a planar network of dislocations just below the surface (spacing 0·2–2 μm). SEM EBIC and CL studies of the layer above the junction revealed dark spots, and a cross‐grid of dark lines, which could be correlated with the threading defects, and the dislocation network just below the surface, respectively. The SEM results showed that these defects had a deleterious effect on the luminescent and electrical properties of the material in the vicinity of the p‐n junction, and would therefore impair the performance of devices made from these layer structures.