Application of Transmission Electron Microscopy to Solving Defect Issues in III-V Alloy Semiconductors and Devices

Abstract

ABSTRACTIn this paper we provide a review of materials issues in the III-V alloy semiconductor system and examine the role of such issues in the degradation of semiconductor lasers and LEDs.Among the major materials issues are the formation of defects and thermal instability of the crystals; we will discuss both of these processes, giving relevant examples. It is convenient to divide crystal defects into two classes: interface defects are bulk defects. Among the former type of defects are stacking faults, V-shaped dislocations, dislocation clusters, microtwins, inclusions and misfit dislocations. Defects belonging to the second class include precipitates and dislocation loops. Thermal instability in crystals during growth also leads to structural imperfections which can affect device properties. One example is the formation of quasi-periodic modulated structures due to spi nodal decomposition of the crystal either at the liquid/solid interface or the growth surface. Another is the formation of ordered structure which also occurs on the growth surface through migration and reconstruction of deposited atoms.We discuss optical device degradation in terms of three major degradation modes: rapid degradation, gradual degradation and catastrophic failure. In devices which degrade by rapid degradation, it is found that recombination-enhanced dislocation glide and climb are responsible. We examine the ease with which these phenomena occur in various hetero-structures and attempt to determine what the dominant parameters are. Gradual degradation takes place presumably due to recombination-enhanced point defect reaction in GaAlAs/GaAs-based optical devices. This degradation mode can be enhanced by the presence of stress due to lattice mismatch in the system. However, in InGaAsPAEnP-based devices, gradual degradation is not observed. In GaAlAs/GaAs DH lasers, catastrophic failure is found to be the result of catastrophic optical damage at a mirror or defect. Again, however, InGaAsP/InP DH lasers do not suffer from this form of degradation. In each degradation mechanism, the role of defects in the degradation and methods of elimination of degradation are discussed.