If μI and μP represent the impurity scattering and phonon scattering limited values of mobility of a semiconductor, the overall mobility would be

• A. μI + μP
• B. \(\frac{{{\mu _I} + {\mu _P}}}{2}\)
• C. \(\sqrt {{\mu _I}{\mu _P}} \)
• D. \(\frac{{{\mu _I}{\mu _P}}}{{{\mu _I} + {\mu _P}}}\)