Profiling the bandgap-adjusted mobility in a bipolar transistor base using the inverse early effect

Abstract

Conventional drift transistor analysis is used to show that C- V and inverse-mode Early data on a large-area bipolar transistor can be combined to yield a profile of μ n × ( N A/ N A A −)e ΔE g / kT with respect to depth (hereafter referred to as an “inverse Early profile”) in the neutral base. This result is then confirmed using a 2-D device simulator to simulate the profile extraction process. The extracted inverse Early profile, obtained from the terminal characteristics of the simulated transistor, agrees with the actual simulator models to better than 10%. An experimental inverse Early profile for an actual transistor is also presented and discussed. Significant advantages of this technique over previous mobility-bandgap model verification and profiling techniques are that specialized structures need not be fabricated, the measurement is simple and nondestructive, and the effects of strain are automatically included in the resulting profile.