Photo-luminescence and transmission electron microscope studies of low- and high-reliability AlGaAs/GaAs HBTs

AlGaAs/GaAs single HBTs from two different epi-layers with similar layer de sign, but with some variations in layer properties due to the particular fe atures of individual epitaxial growth techniques, were simultaneously fabri cated using a self-aligned process. These HBTs were tested for their reliab ility characteristics as well as their material quality using photo-lumines cence and transmission electron microscopy. HBTs from one epi-layer showed high reliability characteristics and presented smaller carrier recombinatio n lifetime (tau(B) approximate to 150 ps) in the base compared to devices f rom the other epi-layer (tau(B) approximate to 60 ps), which showed low rel iability characteristics. Using XTEM images, it was found that devices with higher degree of reliability show abrupt base-emitter junction vs low-reli ability devices, which appeared to have compositionally graded base-emitter hetero-interface. (C) 2000 Published by Elsevier Science Ltd. All rights r eserved.