Variation of Fermi Energy Level and Carrier Concentration with Temperature 
References
Books
S. M. Sze and Kwok K. Ng, Physics of Semiconductor Devices, Wiley-Interscience, 2007.
B. G. Streetman and S. Banerjee, Solid State Electronic Devices, Pearson, 2016.
R. F. Pierret, Semiconductor Device Fundamentals, Addison-Wesley, 1996.