Full two-dimensional electroluminescent (EL) analysis of GaAs-AlGaAs HBTs

This paper describes what is believed to be the first full two-dimensional electroluminescent (EL) analysis of base-emitter junctions in heterojunction bipolar transistors (HBTs). Correlation of the DC and RF characteristics with respect to the changes in EL emission are presented. Special sample preparation techniques and emission microscopy procedures were used to reveal the full electroluminescent pattern from the backside of discrete HBT chips. Sample mounting was optimized to permit inspection at a magnification of 500×. Two parallel emitter fingers, 3 μm by 10 μm each, were easily resolved. This technique is utilized to investigate HBT susceptibility to current driven lattice degradation that manifests itself in nonradiative recombination regions. Occurrence of dark line defects (DLDs) is similar to that reported for solid state lasers and light emitting diodes (LEDs). Rapid changes in the EL pattern occur at current densities of 150 kA/cm². Full two-dimensional electroluminescent analysis represents a breakthrough in the investigation and resolution of current driven degradation in HBT devices because dramatic changes in the optical characteristics occur prior to small changes in the electronic characteristics