Dislocation structure, formation, and minority-carrier recombination in AlGaAs/InGaAs/GaAs heterojunction bipolar transistors

Abstract

The defect structure in lattice-mismatched Al0.25Ga0.75As/InxGa1−xAs/GaAs heterojunction bipolar transistors (HBTs) was investigated using cathodoluminescence (CL), planar and cross-sectional transmission electron microscopy (TEM), and electron-beam-induced current images of the emitter-base and base-collector junctions. It was found that the individual techniques listed above cannot lead to a complete understanding of the defect structure; however, by combining techniques, we are able to derive a detailed knowledge of the dislocation structure, formation, and nonradiative recombination properties in the HBT structures. We find that misfit dislocations predominately form at the mismatched interface located most deeply in the structure. For noninverted HBT structures, which have the AlGaAs emitter/InGaAs base junction on top, we find the majority of misfit defects near the base-collector junction at the bottom InGaAs/GaAs interface. At low dislocation density interfaces, dark line defects observed in CL and misfit dislocations seen in TEM micrographs correlate one to one, but at high densities the dark lines correspond to groups of misfit dislocations. At high In concentrations, a dense network of defects forms at the bottom InGaAs/GaAs interface. The dislocations that are expelled by interdislocation forces from this interface propagate into the GaAs side of the interface, leaving the base region and the emitter-base interface relatively free of misfit dislocations. The relaxation of the strained base by misfit dislocation formation at the InGaAs/GaAs interface is much slower than that predicted using mechanical equilibrium theory. Utilizing the above results, we describe a method for obtaining dislocation-free interfaces in mismatched multilayer structures. This method can be incorporated in lattice-mismatched HBT structures to obtain dislocation-free emitter-base junctions.

Anisotropic strain relaxation of GaInP epitaxial layers in compression and tension

“…Fitzgerald et al observed edge dislocations resulting from the reaction of misfit dislocations below the interface in compressive InGaAs/GaAs heterostructures. 23 They showed that these edge dislocations are formed by the reaction of misfit dislocations expelled from groups of like sign dislocations. Our XTEM studies, however, failed to find such substrate defects.…”

Lattice mismatch and surface morphology studies of In x Ga1−x As epilayers grown on GaAs substrates

“…InGaAs is an interesting material for opto-electronic applications in the range 0.9-3 gtm and also for high speed device applications (Nagai 1974). The advantage of InGaAs/GaAs layers over AIGaAs/GaAs is that the concentration of deep levels which limit the device performance in the latter is reduced (Fitzgerald et al 1988a). However, in the case of InxGa ~ _As layers, lattice mismatch between the epilayer and the substrate creates undesirable lattice defects, especially misfit dislocations at the interface.…”

Misfit dislocations in strained InxGa1−xAs heterostructure on patterned GaAs (001) substrate

“…[10][11][12][13][14][15][16] As the film thickness increases, the ͗110͘ misfit dislocation density increases. The difference in misfit dislocations in the two ͗110͘ directions in structures, with respect to properties and velocity, result in the asymmetric arrangement of misfit dislocations in the two ͗110͘ directions.…”