Semiconductor Physics and Devices

Transcription

1 EE321 Fall 2015 Semiconductor Phyic and Device November 30, 2015 Weiwen Zou ( 邹卫文 ) Ph.D., Aociate Prof. State Key Lab of advanced optical communication ytem and network, Dept. of Electronic Engineering, SEIEE, SJTU wzou@jtu.edu.cn Office: SEIEE building #5-203 ( ) Coure ite: Laboratory P. 0

2 Coure arrangement Chapter Preface & Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 14 Experiment Review Content Overview & The crytal tructure of olid Quantum Mechanic Quantum theory of olid Semiconductor in Equilibrium Carrier tranport phenomena Nonequilibrium exce carrier in emiconductor pn junction pn junction diode Metal emiconductor and emiconductor heterojunction Metal-oxide-emiconductor field-effect tranitor Optical device Simulation and report The above content phyic device Laboratory P. 1

3 Highlight in previou chapter Laboratory P. 2

4 Review (1) : n-type v. p-type emiconductor (ch. 4) n-type: donor impuritie e.g., Silicon (Group IV) + Phophoru (Group V) Energy-band diagram E C p-type: acceptor impuritie e.g., Silicon (Group IV) + Boron (Group III) E F E Fi E V E C E Fi EF EFi n0 ni exp kt i Laboratory P. 3 E F E V Energy-band diagram n p n p E E n kt Fi F 0 i exp

5 Review (2) : Tranport mechanim (Ch. 5) Two baic tranport mechanim in a emiconductor crytal: 1. Drift: the movement of charge due to electric field; 2. Diffuion: the flow of charge due to denity gradient. Total drift current denity: J drift = J p drift + J n drift = e(pμ p + nμ n )E Mobility: μ = v E e τ colliion m impurity cattering) Diffuion current denity: (lattice/phonon or ionized dn J dif = J p dif + J n dif = ed n ed dp dx p dx Laboratory P. 4

6 Chapter 7: The pn junction We now wih to conider the ituation in which a p-type and an n-type emiconductor are brought into cloe contact with one another to form a pn junction. Mot emiconductor device contain at leat one junction between p- type and n-type emiconductor region. Semiconductor device characteritic and operation are intimately connected to thee pn junction. The electrotatic of the pn junction i conidered in thi chapter. The current-voltage (I-V) characteritic of the pn junction diode are developed in the next chapter. Laboratory P. 5

7 Outline of Part I Formation of a pn junction Built-in potential barrier Internal electric field Space charge width Laboratory P. 6

8 Schematic of the pn junction ymbol The pn junction formed by the cloe contact of an n- type and p-type region i a ingle emiconductor ytem. n-type region (doped with donor impurity, N D ) + p-type region (doped with acceptor impurity, N A ) The interface i referred to a the metallurgical junction. Laboratory P. 7

9 Formation of the pn junction Laboratory P. 8

10 Formation of the pn junction (cont.) Laboratory P. 9

11 Formation of the pn junction (cont.) Laboratory P. 10

12 Space charge region The net poitively charged region (ionized donor) The net negatively charged region (ionized acceptor) An electric field [E 0 (or E 0 )] i formed. E 0 (or E 0 ) Laboratory P. 11

13 Depletion region (DR, Space charge region) Eentially, all electron in the n-type ide and all hole in the p-type are wept out of the pace charge region by the electric field. Since there i no any mobile charge in the pace charge region, it i called the depletion region a well. E 0 (or E 0 ) Laboratory P. 12

14 Diffuion force and E-field force Diffuion force : denity gradient Electric field force: the oppoite charged ion In thermal equilibrium, they exactly balance each other. Laboratory P. 13

15 Outline of Part I Formation of an pn junction Built-in potential barrier Internal electric field Space charge width Laboratory P. 14

16 Energy-band diagram of the pn junction p-type n-type E C Neutral p-region E Fi E F E C E F E V When no voltage i applied acro the pn junction and the pn junction i in thermal equilibrium, the Fermi energy level i contant through the entire ytem. Depletion region Laboratory P. 15 Neutral n-region E Fi E V

17 Built-in potential barrier Electron in the conduction band of the n region (right ide) feel a potential barrier when trying to move into the conduction band of the p region (left ide). Thi potential barrier i called built-in potential barrier (alo junction barrier), denoted by V bi. Laboratory P. 16 E C E F E V p-type Neutral p-region Depletion region n-type Neutral n-region The barrier i internal. Effort to meaure it at the terminal of the emiconductor will ee no potential difference. It maintain equilibrium of the entire ytem. No current i produced by thi internal voltage (no mobile carrier). E Fi V bi E C E F E Fi E V

18 Derivation of built-in potential barrier Define the potential φ Fn and φ Fp a hown in the right figure V bi = φ Fn + φ Fp Define the potential φ Fn in the n region a eφ Fn = E Fi E F E C E Fi E F E V p-type Neutral p-region eφ Fp n-type V bi Neutral n-region eφ Fn E C E F E Fi E V Depletion region n 0 =N d Note: N d ->N d -N a (n) (compenated n-type) N d e Fn EFi EF kt ln ni Laboratory P. 17 Similarly, N a e Fp EFi EF kt ln ni p 0 =N a Note: N a ->N a -N d (p) (compenated p-type)

19 Derivation of built-in potential barrier (cont.) Define the potential φ Fn and φ Fp a hown in the right figure V bi = φ Fn + φ Fp E C E Fi E F E V p-type Neutral p-region eφ Fp n-type V bi eφ Fn E C E F E Fi Neutral n-region E V V kt NN a d ln 2 e ni bi Fn Fp Depletion region NN a d Vbi Vt ln 2 ni V kt / e--thermal voltage (V) t Laboratory P. 18

20 Example 1 Quetion: Laboratory P. 19

21 Example 2 Quetion: = V The built-in potential barrier change only lightly a the doping concentration change by order of magnitude. Thi i due to the log dependence. Laboratory P. 20

22 Outline of Part I Formation of an pn junction Built-in potential barrier Internal electric field Space charge width Laboratory P. 21

23 Poion equation (one dimenion) An electric field i created in the depletion region by the eparation of poitive and negative charge denitie. Aumption of uniform doping and an abrupt junction The electric field i determined from Poion equation (in one dimenion): x de x dx x de x d 2 x dx =- d x dx dx 2 E x Laboratory P. 22

24 Internal electric field x en en a a E dx dx x C1 x en en d d E dx dx x C2 Boundary condition: E(x = x p or + x n ) = 0 C C 1 en en a x x p en a E x xp en d d 2 n E xn x OFS 3 : Optical Fiber Senor & Signal proceing Sytem Laboratory P. 23

25 Neutrality in the pace charge region Laboratory P. 24 Continuou condition of the electric field at the metallurgical junction (x=0): E en x a p d n The neutrality in the pace charge region: N x a p d x x p n N x N N d a en x

26 Potential in the pace charge region or DR p-type n-type E C Neutral p-region E Fi E C E F E F E V E Fi x E x dx Neutral n-region E V E nergy ( x)=-e Depletion region Laboratory P. 25 x

27 Potential in the pace charge region (cont.) en 2 a x x x x x 0 2 en p 2 x en 2 2 a a 2 x x x x 0 x x n p n e V x x N x N x bi n d n a p p Energy band Electric field Φ=0 Electric potential p E -x p x n x=0 n Φ=V bi Laboratory P. 26

28 Outline of Part I Formation of an pn junction Built-in potential barrier Internal electric field Space charge width Laboratory P. 27

29 Space charge width Neutrality: N x Potential barrier: Charge width at each ide: N x a p d n e V x x N x N x 2 x x 2 2 bi n d n a p n p 2 V bi N a 1 e Nd Na Nd 2 V bi N d 1 e Na Na Nd 1/ 2 1/ 2 x x p n N N d a Space charge width: 2 V bi N a N W x d n xp e NaNd 1/ 2 Laboratory P. 28

30 Example 3 Quetion: Laboratory P. 29

31 One-ided junction Conider a pecial pn junction called the one-ided junction. For example, Let N a >> N d. Thi junction i referred to a a p + n junction. x Since : x p n Thu: x n N N d a >> x p Thu: W x n Almot the entire pace charge layer extend into the low-doped region of the junction. Laboratory P. 30

32 Summary: Expreion of ρ, E, φ, and W Ditribution of charge ρ x > 0 = en d ρ x < 0 = en a Electric field E = en d ε E = en a ε x n x, x > 0 x p + x, x < 0 Potential voltage φ = en a 2ε x p 2 + en a ε φ = en d 2ε x n x x2 2 x p + x 2, x < 0, x > 0 Space charge width x n 2 V bi N a 1 e Nd Na Nd x p 1/2 2 V bi N d 1 e Na Na Nd 1/2 W x x n p 2 V N N e NaNd bi a d 1/2 Laboratory P. 31

33 Semiconductor Phyic and Device Pleae come back thi Wedneday. End of Day #12 Weiwen Zou ( 邹卫文 ) Ph.D., Aociate Prof. State Key Lab of advanced optical communication ytem and network, Dept. of Electronic Engineering, SEIEE, SJTU wzou@jtu.edu.cn Office: SEIEE building #5-203 ( ) Coure ite: Laboratory P. 32