Reading Materials

Breakdown voltage VB depends on the doping density of a pn junction，in particular on the doping of the more lightly doped side of the junction. Fig 8.7 shows a plot of breakdown voltage for Si diodes of different doping. It indicates the general value of the quantities，but does not account for the grading of the junction，the doping of the more heavily doped side，nor the distinction between a planarand a spherical junction .

The mechanism of breakdown for p-n junctions with breakdown voltages less than about 4Eq/q is due to the tunneling effect. For junctions with breakdown voltages in excess of 6Eq/q，the mechanism is caused by avalanche multiplication. At voltages between（4～6）Eq/q，the breakdown is due to a mixture of both avalanche and tunneling.

Although not large，the temperature variation of the two types of breakdown is of opposite sign. For breakdown voltages in the range of about 5～6 V for a Silicon diode，both avalanche-and tunnel-breakdown can occur simultaneously so that the net temperature variation is very slight. This characteristic is useful for establishing a voltage referencein some integrated circuits.

Words and Expressions

collide v. 碰撞

predominant adj. 主要的

sinusoidal adj. 正弦的

to superimposed on 叠加在……上

accompany v. 伴随，伴有

dominant adj. 占主要地位的

associated with adj. 与……有关

reciprocal adj. 倒数的

to be inversely proportional to… 与……成反比

to be directly proportional to… 与……成正比

inverse square root 负二分之一次方

differentiate v. 求导

Keep in mind that… 记住……

Glossary of Important Term

breakdown 击穿

avalanche breakdown 雪崩击穿

ionize 离化

Zener breakdown 齐纳击穿

tunneling mechanism 隧穿机理

thermal voltage 热电压

DC quiescent diode current 二极管静态直流电流

varactor diode 变容二极管

junction capacitance 结电容

permittivity 介电常数

diffusion capacitance 扩散电容

storage capacitance 储存电容

transit time 渡越时间

a. c. signal 交流信号

sinusoidal signals 正弦信号

infinitesimal voltage 无穷小电压

incremental conductance 增量电导

diffusion resistance 扩散电阻

linear amplifier circuits 线性放大电路

electrical switch 电开关

pulse 脉冲

‘on’ state 导通状态

‘off’ state 断开状态

turn-on time 导通时间

turn-off time 断开时间

transient 瞬态

storage time 储存时间

fall time 下降时间

simulation 模拟，仿真

equivalent circuit 等效电路

integrated circuit 集成电路

planar junction 平面结

spherical junction 球面结

voltage reference 电压基准

Exercises

1. Translate the reading material into Chinese.

2. How to avoid the destruction of a device resulted from the breakdown.

3. Compare the differences between the avalanche-breakdown and tunnel-breakdown.

4. Why docs the breakdown voltage of a pn junction decrease as the doping concentration increases？

5. Why does a junction capacitance exist in a biased pn junction？

6. Explain the physical mechanism of diffusion capacitance.

7. Compare the differences between the Voltage dependences of the small-signal junction capacitance Cj and diffusion capacitance Cd of a junction diode.

8. Explain what is diffusion resistance and why it is dependent on the dc quiescent diode current？

9. Why would some time be required to make the transition of a diode from off to on（turn-on time）and from on to off（turn-off time）？

10. When and why must the small-signal equivalent circuit be used？