Extraction of bipolar SPICE Gummel-Poon parameters related to B-C junction Capacitance-Voltage (C-V) 
References
Books
Ian Getreu, Modeling the Bipolar Transistor, Tektronix, Inc., 1976. (This is the definitive guide. It provides the exact, practical methods for measuring the B-C capacitance and extracting CJC, VJC, and MJC from the C-V plots.)
S. M. Sze and Kwok K. Ng, Physics of Semiconductor Devices, 3rd ed., Wiley, 2006. (Provides the core semiconductor physics explaining the B-C depletion capacitance and how the $1/C^2$ vs. $V$ plot relates to the junction's doping profile and built-in potential.)
G. Massobrio and P. Antognetti, Semiconductor Device Modeling with SPICE, 2nd ed., McGraw-Hill, 1993. (Details the specific Gummel-Poon SPICE equations for the B-C capacitance ($C_{bc}$) and explains the roles of CJC, VJC, MJC, and the reverse transit time TR.)