Reading Materials

So-called ‘forward on voltage’

In the forward direction，the current rises very rapidly but smoothly as shown in Fig.7.4（a），and there is no real ‘forward on voltage ’ as sometimes assumed in books on circuit theory. 19. In the forward direction，the current rises very rapidly but smoothly as shown in Fig.7.4（a），and there is no real ‘forward on voltage’ as sometimes assumed in books on circuit theory. 提示：句子的and具有转折的含义，因此将and there is no翻译为“并不存在”；books on …表示“关于……方面的书”；本句中assume表示“呈现，表现”的意思，不要总是翻译为“假设”。 However，as Fig.7.6 shows，in strong forward bias，the diode voltage varies rather little over a wide current range. 20. However，as Fig.7.6 shows，in strong forward bias，the diode voltage varies rather little over a wide current range. 提示：in strong forward bias 表示正偏电压较大，其中的strong不要翻译为“强”；rather是副词，修饰little，表示相当小。

Fig.7.6 The current-voltage characteristic.

For example，a diode designed to carry a current I at，say，0.6V（i. e. eVa/kT=24）will carry a current of only 0. 001 I at 0.427 V（eVa/kT=17.1）. 21. For example，a diode designed to carry a current I at，say，0.6 V（i. e. eV/kT=24）will carry a current of only 0. 001 I at 0.427 V（qV/kT=17.1）. 提示：这是个简单句，主语是a diode，谓语是will carry，其中主语后面带有过去分词designed引导的限制性定语；句子的say是插入语，假设一种情况，可以翻译为“例如”，并且具有以该假设情况为例说明某个结论的作用；i. e. 是拉丁语，代表that is，可翻译为“也就是”或者“即”；本句采用“意译”的方式可以很简洁地将全句的含义表达清楚。 For practical purposes the diode is ‘off’ below this voltage.

The difference in the ‘on’ voltages of Ge and Si diodes also needs explanation. Note the ‘on’ current for a Ge diode with the same applied voltage as an Si diode（e. g. 0.7V）is the same multiple of its reverse saturation current IS. Since IS is proportional to the minority carrier density，which in turn depends on n2i，the reverse saturation current of a Ge diode-and hence the forward current-is about 108 times that of an Si diode with the same doping levels. 22. Since IS is proportional to the minority carrier density，which in turn depends on n2i，the reverse saturation current of a Ge diode-and hence the forward current-is about 108 times that of an Si diode with the same doping levels. 提示：which in turn depends on n2i是非限制性定语从句，修饰the minority carrier density；and hence the forward current引导的句子中谓语与the reverse saturation current of a Ge diode的谓语相同，因此省略了。 Thus a Ge diode ‘turns on’ at a lower voltage-about 0.25V is typical. Note that，to make a Si diode turn on at this voltage would need either a doping level about 108 times smaller，or an area 108 times bigger：neither is a practical proposition. 23. Note that，to make an Si diode turn on at this voltage would need either a doping level about 108 times smaller，or an area 108 times bigger：neither is a practical proposition. 提示：这是由Note引导的祈使句，后面是宾语从句；宾语从句中谓语need后面是由either …，or…引导的两个宾语；代词neither作主语引导的简单句对前面内容起补充说明的作用，其中neither的含义是not either，用于对前面either …，or…内容的否定；proposition的含义是suggestion。

Words and Expressions

intimately adv. 密切地

terminology n. 术语

imperfection n. 不完整性，缺陷

indefinitely adv. 无限期地

interchangeably adv. 可交换地

respectively adv. 分别地

dramatically adv. 引入注目地，明显地

semilog n. 半对数

decade n. 十（进制，位）

denominator n. 分母

exponent n. 指数

square root n. 平方根

proposition n. 提议

characteristics n. 特性

operation n. 工作

celebrated adj. 著名的

profile n. 剖面

quantitative analysis 定量分析

techniques n. 技术

to allow for 考虑

to be referred to… as… 将……称为……

be depleted of … 耗尽……

be worthwhile ～ing 值得……

to prevent … from ～ing 阻止……（做……）

Glossary of Important Term

semiconductor device 半导体器件

pn junction pn结

diode 二极管

rectifier 整流器

switching circuit 开关电路

metallurgical junction 冶金结

step junction 突变结

space charge region 空间电荷区

depletion region 耗尽层

depletion-layer width 耗尽层宽度

reverse bias 反向偏置

forward bias 正向偏置

low injection 小注入

high-injection 大注入

continuity equation 连续性方程

current-voltage characteristics 伏安特性

Shockley equation 肖克莱方程

ideal diode law 理想二极管定律

saturation current 饱和电流

series resistance 串联电阻

breakdown 击穿

forward on voltage 正向导通电压

Exercises

1. Translate the reading material into Chinese.

2. Draw the energy band diagram of a zero-biased，forward-biased and reverse-biased pn junction.

3. Describe why and how the space charge region is formed，and what happens to the parameters of the space charge region when a reverse bias voltage is applied.

4. What is the difference between the I-Vcharacteristics of a practical pn junction diode and the ideal pn junction？

5. Summary the main factors causing the departures of a practical pn junction diode from the ideal pn junction.

6. How to understand the so-called ‘forward on voltage’ of a pn junction？

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