Comparative analysis of minority carrier transport in npn bipolar transistors with Si, Si1-xGex, and Si1-yCy base layers

Here we present a comparative analysis of vertical minority carrier transpo rt in Si, Si0.925Ge0.075,Si0.998C0.002, and Si0.99C0.01 base layers of bipo lar transistors. We show that a conventional transit time analysis for extr acting the minority carrier mobilities fails for doping profiles containing a low doped emitter region. The contribution of locally compensated charge storage, called neutral charge storage, in the emitter-base depletion regi on must not be neglected. To overcome drawbacks of the simple transit time analysis, we use 2D device simulations to obtain an improved understanding of the measured high-frequency parameters. Taking into account the real dop ing profiles and device structures, and using a calibrated parameter set fo r strained SiGe, the simulation results for the Si, Si1-xGex, and Si1-yCy ( y less than or equal to 0.2%) base layer transistors reproduce very well th e measured transit times (assuming the Si data for the electron mobility mu (n)) in the heteroepiaxial base layers. In the case of higher carbon concen tration (y = 1%), the electron mobility is reduced by a factor of two. (C) 2000 Elsevier Science S.A. All rights reserved.