如果将P型半导体的块与下图（a）图中的N型半导体块接触，则结果无值。我们有两个导电块相互接触，没有显示独特的属性。问题是两个独立的晶体。电子的数量与两个块中质子的数量平衡。因此，两个块都没有任何净收费。
However, a single semiconductor crystal manufactured with P-type material at one end and N-type material at the other in Figure below (b) has some unique properties. The P-type material has positive majority charge carriers, holes, which are free to move about the crystal lattice. The N-type material has mobile negative majority carriers, electrons. Near the junction, the N-type material electrons diffuse across the junction, combining with holes in P-type material. The region of the P-type material near the junction takes on a net negative charge because of the electrons attracted. Since electrons departed the N-type region, it takes on a localized positive charge. The thin layer of the crystal lattice between these charges has been depleted of majority carriers, thus, is known as thedepletion region。It becomes nonconductive内在的半导体材料。实际上，我们几乎有一个绝缘子，将导电P和N掺杂区分开。
(a) Blocks of P and N semiconductor in contact have no exploitable properties. (b) Single crystal doped with P and N-type impurities develop a potential barrier.
PN连接处的电荷分离构成了潜在的障碍。必须通过外部电压源来克服这种潜在的障碍，才能实现连接行为。结和潜在障碍的形成发生在制造过程中。潜在屏障的大小是制造中使用的材料的函数。硅PN连接处的潜在屏障比锗连接处更高。
在图下面(a)电池是这样安排的the negative terminal supplies electrons to the N-type material. These electrons diffuse toward the junction. The positive terminal removes electrons from the P-type semiconductor, creating holes that diffuse toward the junction. If the battery voltage is great enough to overcome the junction potential (0.6V in Si), the N-type electrons and P-holes combine annihilating each other. This frees up space within the lattice for more carriers to flow toward the junction. Thus, currents of N-type and P-type majority carriers flow toward the junction. The recombination at the junction allows battery current to flow through the PN junction diode. Such a junction is said to beforward-biased。
(a) Forward battery bias repels carriers toward the junction, where recombination results in battery current. (b) Reverse battery bias attracts carriers toward battery terminals, away from the junction. Depletion region thickness increases. No sustained battery current flows.
If the battery polarity is reversed as in Figure above(b) majority carriers are attracted away from the junction toward the battery terminals. The positive battery terminal attracts N-type majority carriers, electrons, away from the junction. The negative terminal attracts P-type majority carriers, holes, away from the junction. This increases the thickness of the nonconducting depletion region. There is no recombination of majority carriers; thus, no conduction. This arrangement of battery polarity is calledreverse bias。
这diode原理图符号如图下所示(b)corresponding to the doped semiconductor bar at (a). The diode is aunidirectional设备。电流仅沿一个方向流动，与箭头旁边，对应于正向偏置。二极管符号的阴极，杆对应于N型半导体。阳极箭头对应于P型半导体。要记住这种关系，not-pointing (bar) on the symbol corresponds ton-type semiconductor.pointing (arrow) corresponds top-type.
（a）向前偏置的PN连接，（b）相应的二极管原理图符号（c）硅二极管I与V特征曲线。
If a diode is forward biased as in Figure above(a), the current will increase slightly as the voltage is increased from 0 V. In the case of a silicon diode a measurable current flows when the voltage approaches 0.6 V in Figure above(c). As the voltage increases past 0.6 V, current increases considerably after the knee. Increasing the voltage well beyond 0.7 V may result in high enough current to destroy the diode. The forward voltage, VF, is a characteristic of the semiconductor: 0.6 to 0.7 V for silicon, 0.2 V for germanium, a few volts for Light Emitting Diodes (LED). The forward current ranges from a few mA for point contact diodes to 100 mA for small signal diodes to tens or thousands of amperes for power diodes.
如果二极管反向偏置，则只有内在半导体流的泄漏电流。这是在（c）上图中原点的左侧绘制的。对于硅小信号二极管的最极端条件，该电流只能高达1 µA。直到二极管分解之前，这种电流不会随着反向偏置的增加而明显增加。在故障时，电流的增加幅度很大，以至于除非高串联电阻限制电流，否则二极管将被破坏。我们通常选择具有比任何施加电压更高的反向电压额定值的二极管以防止这种情况。硅二极管通常可获得50、100、200、400、800 V及更高的反向分解等级。可以用较低的几伏用作电压标准的二极管制造二极管。
我们之前提到，硅二极管下µA下的反向泄漏电流是由于内在半导体的传导。这是可以用理论解释的泄漏。热能会产生很少的电子孔对，该电子孔对导致泄漏电流直至重组。在实际实践中，这种可预测的电流只是泄漏电流的一部分。大部分泄漏电流是由于表面传导引起的，这与半导体表面缺乏清洁度有关。两种泄漏电流随温度的升高而增加，对于小硅二极管接近µA。
For germanium, the leakage current is orders of magnitude higher. Since germanium semiconductors are rarely used today, this is not a problem in practice.
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