陈世棉96-97-A48.doc

CHAPTER 3 The Semiconductor in Equilibrium Solution Equation () can be written as)( 2 210FCFNn??? Form figure , the Fermi-Dirac integral has a value of)3( 21F? 320 19 010 26 .1)4 )(10 ( 2 ????? cm n? Comment Note that if we had used Equation (), the thermal-equilibrium value of the electron concentration would be 320 010 62 .5 ??? cm n which isa factor of approximation too large. When the Fermi level is in the conduction band, the Boltzmann approximation isno longer valid so that Equation () isno longer valid. ExerciseProblem _________________________________________________________ Calculate the thermal- equilibrium electron concentration is silicon at300k for the case when CFEE?.【 Ans. 319 02110 15 .268 .0)( ???? cm son F F?】________________________________________________________________________ We can use the same general method to calculate the thermal-equilibrium concentration of holes obtain )'' exp( 1 ')'() 2(4 210 2 32 *0F Pdh KT mP??????????( ) where KT EE FV??'?( ) and KT EE FVF??'?( ) The integral in equation () is the same Fermi-Dirac integral defined by Equation (), although the variables have slightly different definitions. We can note that if F'?>0, then the Fermi level is in the valence band Degenerate and Nondegenerate Semiconductors Inour discussion of adding dopant atoms toa semiconductor, we h