文章目錄
寫在前面
從第一篇文章開始：半導體基礎知識（1）：材料和器件，覺得挺好，於是決定翻譯第二篇，有緣看到就進行下去。
上篇最後預留了這樣一句話：
如果目標是製造有用的電子組件，那麼摻雜材料本身並沒有比原始半導體更好。 但是，當我們將n型半導體與p型半導體相鄰放置時，一切都會改變。 此結構稱爲pn結，是下一個教程的主題。
這恰好呼應地也是這篇文章，單純的摻雜可沒什麼好說的，要對目標有用，纔是摻雜的目的。我們要用摻雜的半導體材料做成有用的電子器件，就需要將摻雜後的n型半導體和p型半導體相鄰放置！
原文鏈接：The PN Junction Diode and Diode Characteristics
該篇教程探討了通過將n型半導體材料與p型半導體材料接觸而形成的電子結構的物理和電氣行爲。
正文
半導體組件（不僅是二極管和晶體管，而且是不常見的設備，例如TRIAC和可控硅的開關）是通過組合n型和p型半導體而構成的。 因此，重要的是要了解在n型和p型材料之間的界面處會發生什麼。 我們將此接口稱爲pn結。
pn結和半導體二極管
當我們專注於半導體操作的物理學時，我們使用術語pn結； 當我們專注於電路設計時，我們使用二極管一詞。 但是它們本質上是同一回事：基本的半導體二極管是連接有導電端子的pn結。 首先讓我們看一下圖表，然後我們將簡要探討這個極爲重要的電路元件的行爲。
左邊的實心圓是空穴，右邊的實心圓是電子。耗盡區由與來自n型半導體的自由電子重新結合的空穴（這些重新結合的空穴由帶圓圈的負號表示）和與來自p型半導體的空穴重新結合的電子（以圓圈正號表示）組成。該複合導致耗盡區的p型部分帶負電，並且耗盡區的n型部分帶正電。
在p型和n型材料的接合處電荷的分離會導致電位差，稱爲接觸電位。在硅pn結二極管中，接觸電勢約爲0.6V。如上圖所示，該電勢的極性與我們預期的相反：在n型側爲正，而在p型側爲負。
電流可以通過擴散流過結-由於結兩部分的電荷載流子濃度不同，一些來自p型材料的空穴將擴散到n型材料中，而一些來自n型電子型材料將擴散到p型材料中。但是，幾乎沒有電流流過，因爲接觸電勢對該擴散電流起阻擋作用。此時，我們將開始使用術語勢壘電壓代替接觸電勢。
正向和反向偏置
如果我們將二極管連接到電池上，使得電池的電壓與勢壘電壓具有相同的極性，則結點將被反向偏置。 由於我們正在增加勢壘電壓，因此擴散電流進一步受到阻礙。
施加反向偏置電壓會使結的耗盡區變寬。
另一方面，如果我們將電池的正極連接到二極管的p型側，而負極將連接到n型側，則我們正在降低勢壘電壓，從而促進電荷載流子在結上的擴散。 但是，在我們克服勢壘電壓並完全耗盡耗盡區之前，電流量將保持相當低的水平。 這在施加的電壓等於勢壘電壓時發生，並且在這些正向偏置條件下，電流開始自由流過二極管。
二極管作爲電路組件
前面的討論揭示了產生硅二極管電行爲的兩個最突出特徵的基本物理過程。
首先，當以反向偏壓極性施加電壓時，pn結阻止電流流動，而當以正偏壓極性施加電壓時，pn結允許電流流動。 這就是爲什麼二極管可以用作電流的單向閥的原因。
其次，當施加的正向偏置電壓接近勢壘電壓時，流過二極管的電流呈指數增長。 這種指數電壓-電流關係使正向偏置二極管的電壓降保持相當穩定，如下圖所示。
二極管的工作量可以近似爲一個恆定的電壓降，因爲很小的電壓增加對應於很大的電流增加。
下圖闡明瞭二極管的物理結構，其電路符號以及我們用於其兩個端子的名稱之間的關係。 施加正向偏置電壓會使電流沿藍色箭頭方向流動。
結論
現在，我們已經介紹了半導體功能的基本方面，並且在下一個教程中，我們將探討晶體管，這是迎來電子時代的半導體組件。
原文附錄
Semiconductor components—not only diodes and transistors but also less-common devices such as TRIACs and silicon-controlled switches—are constructed by combining n-type and p-type semiconductors. Thus, it is important to understand what occurs at the interface between n-type and p-type materials; we call this interface the pn junction.
The pn Junction and the Semiconductor Diode
When we’re focusing on the physics of semiconductor operation, we use the term pn junction; when we’re focusing on circuit design, we use the term diode. But they’re essentially the same thing: a basic semiconductor diode is a pn junction with conductive terminals attached. First let’s look at a diagram, and then we’ll briefly explore the behavior of this extremely important circuit element.
The unfilled circles on the left are holes, and the solid circles on the right are electrons. The depletion region consists of holes that have recombined with free electrons from the n-type semiconductor (these recombined holes are represented by circled negative signs) and electrons that have recombined with holes from the p-type semiconductor (represented by circled positive signs). This recombination causes the p-type portion of the depletion region to be negatively charged and the n-type portion of the depletion region to be positively charged.
The separation of charge at the junction of the p-type and n-type materials results in a potential difference called the contact potential. In a silicon pn-junction diode, the contact potential is about 0.6 V. As you can see in the previous diagram, the polarity of this potential is the opposite of what we might expect: it is positive on the n-type side and negative on the p-type side.
Current can flow through the junction by means of diffusion—because of differences in charge-carrier concentrations in the two portions of the junction, some holes from the p-type material will diffuse into the n-type material, and some electrons from the n-type material will diffuse into the p-type material. However, very little current flows because the contact potential functions as a barrier to this diffusion current. At this point we will begin using the term barrier voltage instead of contact potential.
Forward and Reverse Bias
If we connect the diode to a battery such that the battery’s voltage has the same polarity as the barrier voltage, the junction is reverse-biased. Diffusion current is further impeded because we are increasing the barrier voltage.
Applying a reverse-bias voltage widens the junction’s depletion region.
If, on the other hand, we connect the battery’s positive terminal to the p-type side of the diode and the negative terminal to the n-type side, we are decreasing the barrier voltage and thereby facilitating charge-carrier diffusion across the junction. However, the amount of current will remain quite low until we overcome the barrier voltage and fully collapse the depletion region. This occurs when the applied voltage is equal to the barrier voltage, and under these forward-biased conditions, current begins to flow freely through the diode.
Diodes as Circuit Components
The preceding discussion reveals the underlying physical processes that produce the two most prominent characteristics of a silicon diode’s electrical behavior.
First, a pn junction resists current flow when voltage is applied in reverse-bias polarity and allows current flow when voltage is applied in forward-bias polarity. This is why a diode can function as a one-way valve for electric current.
Second, current flow through a diode increases exponentially as the applied forward-bias voltage approaches the barrier voltage. This exponential voltage–current relationship causes the voltage drop of a forward-biased diode to remain fairly stable, as conveyed by the following plot.
Diode operation can be approximated as a constant voltage drop because large increases in current correspond to very small increases in voltage.
The following diagram clarifies the relationship between the physical structure of a diode, its circuit symbol, and the names that we use for its two terminals. Applying a forward-bias voltage causes current to flow in the direction of the blue arrow.
Conclusion
We have now covered foundational aspects of semiconductor functionality, and in the next tutorial we’ll explore the transistor, which is the semiconductor component that ushered in the electronic age.