什么是半导体? 物体的导电能力,一般用材料电阻率的大小来衡量。 电阻率越大,说明这种材料的导电能力越弱。下表给 出以电阻率来区分导体,绝缘体和半导体的大致范围。 物体 导体半导体绝缘体 电阻率 2·cM|<10e-410e 3~10e9 >10e9
1 1 什么是半导体？
Band Theory of bonding in Sol ids Changing from“Bond"to“Band” In solid where huge number of atoms exist closely pack ) discrete MOs become continuous bands erets 3X1029 ±))(+(+) +) 25 Fig. 6. 9 Electron sea model for metals 2e
2 2 Band Theory of Bonding in Solids ⚫ Changing from “Bond” to “Band” ◼ In solid where huge number of atoms exist (& closely pack), discrete MOs become continuous bands. 2
Band structures Valence Band(Bonding orbitals in Mo) Conduction Band(Nonbonding orbitals in MO Band gap(Ea Fermi energy(in metal) Conduction conduction Conductor Valence Band Eg -0 Semiconductor =Vacant states insulator Metal □=0 coupled sites Insulator @995 CHP 3
3 3 Band Structures ⚫ Valence Band (Bonding orbitals in MO) ⚫ Conduction Band (Nonbonding orbitals in MO) ⚫ Band gap (Eg ) ⚫ Fermi energy (in metal) 3
半导体与金属的电阻率随温度的变化 温度
4 4 半导体与金属的电阻率随温度的变化
材料的费米能级(E) n(e) 空穴 电子 F ig. 24. Fermi-Dirac distribution at T=C, stoke
5 5 材料的费米能级（EF）