Properties of fully self-aligned InAlAs/InGaAs PNP HBTs with very thin bases

Abstract

For the first time, the effect of base thickness and parasitic collector resistance on InP-based PNP HBTs was determined experimentally. HBTs with 350-/spl Aring/ and 900-/spl Aring/ base layers and self-aligned collector contacts demonstrated DC gain of 21.3 and 5.9, f/sub T/ of 18.6 and 8.5 GHz, and f/sub max/ of 27.3 and 20.8 GHz, respectively. This is the highest f/sub T/ reported for any InP-based PNP HBT. Analysis of these HBTs demonstrated that recombination of holes in the neutral base limited the DC gain, and hole transit across the base was the most significant component of /spl tau//sub ec/. In addition, comparison of HBTs with and without self-aligned collectors demonstrated that collector series resistance had a minor but noticeable impact on f/sub T/ as well as the gain and power-added efficiency at 8 GHz.