Characterization of Current-Induced Degradation in Be-Doped HBT's Based in GaAs and InP

The changes in the device characteristics under high-bias conditions are investigated for InAlAs/InGaAs and AlGaAs/GaAs heterojunction bipolar transistors (HBT's) with heavily Be-doped base layers. While the collector current turnon voltage shift in AlGaAs/GaAs HBT's has been well-studied, we focus on the base current and 1 /f noise characteristics. It is shown that the ideality factor of the surface recombination base current provides information on the Be movement accompanying the degradation. For stress current densities up to 1.5 x 105 A/cm2, the Be movement in the InAlAs/InGaAs HBT's is estimated to be no more than a small fraction of the 5-nm setback layer. The 1/f noise measurements highlight the effect of current stressing on the surface recombination in the HBT's. A characteristic spectral shape is found in the noise spectra for the current-stressed AlGaAs/GaAs HBT, possibly originating from the degradation-induced carrier traps. Although both HBT's have similar electronic properties, these results illustrate the striking difference in their stress current behaviors.