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 transport in Si, Si 0.925 Ge 0.075 , Si 0.998 C 0.002 , and Si 0.99 C 0.01 base layers of bipolar transistors. We show that a conventional transit time analysis for extracting 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 region 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 doping profiles and device structures, and using a calibrated parameter set for strained SiGe, the simulation results for the Si, Si 1-x Ge x , and Si 1-y C y (y ≤ 0.2%) base layer transistors reproduce very well the measured transit times (assuming the Si data for the electron mobility μ n ) in the heteroepiaxial base layers. In the case of higher carbon concentration (y = 1%), the electron mobility is reduced by a factor of two.

[1]  D.B.M. Klaassen,et al.  A unified mobility model for device simulation—I. Model equations and concentration dependence , 1992 .

[2]  R. People,et al.  Physics and applications of Ge x Si 1-x /Si strained-layer heterostructures , 1986 .

[3]  M. Stettler,et al.  A microscopic study of transport in thin base silicon bipolar transistors , 1994 .

[4]  Karl Eberl,et al.  Pseudomorphic Si1−yCy and Si1−x−yGexCy alloy layers on Si , 1997 .

[5]  D. Ritter,et al.  Electron transport in heavily doped bases of InP/GaInAs HBT's probed by magneto transport experiments , 1996 .

[6]  J.A. del Alamo,et al.  Measurement of hole mobility in heavily doped n-type silicon , 1986, IEEE Electron Device Letters.

[7]  W. Kuzmicz.  Ionization of impurities in silicon , 1986 .

[8]  J.W. Slotboom,et al.  On the Optimisation of SiGe-Base Bipolar Transistors , 1995, ESSDERC '95: Proceedings of the 25th European Solid State Device Research Conference.

[9]  I. Getreu,et al.  Modeling the bipolar transistor , 1978 .

[10]  A. Gopinath,et al.  Accurate measurement technique for base transit time in heterojunction bipolar transistors , 1991 .

[11]  J.J.H. van den Biesen,et al.  A simple regional analysis of transit times in bipolar transistors , 1986 .

[12]  B Heinemann,et al.  Influence of low doped emitter and collector regions on high-frequency performance of SiGe-base HBTs , 1995 .

[13]  J. Slotboom,et al.  Unified apparent bandgap narrowing in n- and p-type silicon , 1992 .