Basic semiconductor crystal structure.docVIP

Basic semiconductor crystal structureTo understand how diodes,transistors,and other semiconductor devices can do what they do,it is first necessary to understand the basic structure of all semiconductor devices.early semiconductors were fabricated from the element germanium,but silicon is preferred in most modern applications.The crystal structure of pure silicon is of course 3-dimensional,but that is difficult to display or to see,so the image to the left is often used to represent the crystal structure of silicon.for you physics types,silicon(and germanium)falls in column a of the periodic table.T.his is the carbon family of elements.the essential characteristic of these elements is that each atom has four electrons to share with adjacent atoms in forming bonds.While this is an oversimplified description,the nature of a bond between two silicon atoms is such that each atom provides one electron to share with the other .The two electrons thus shared are in fact shared equally between the two atoms.This type of sharing is known as a covalent bond.such a bond is very stable ,and holds the two atoms together very tightly,so that it requires a lot of energy to break this bond.了解二极管、晶体管和其他半导体器件可以发挥他们的功效，首先需要理解所有半导体器件的基本结构。早期的半导体制造从元素锗开始,但硅在大多数现代应用程序中优先使用。当然纯硅的晶体结构是三维,但这很难显示或看到,所以左侧图像常被用来代表硅的晶体结构。你物理类型、硅和锗落在列a周期性table.T。他是碳元素的家庭。这些元素的基本特点是,每个原子有四个电子与相邻原子形成分享债券。虽然这是一个过于简单化的描述,两个硅原子之间的键的性质,每个原子都提供一个电子来分享。两个电子从而共享实际上是两个原子之间的平均分担。这种类型的共享称为共价键。这种债券是非常稳定的,把两个原子结合在一起非常紧密,所以,它需要大量的能量来打破这种债券。For those who are interested,the actual bones in a 3-dimensional silicon crystal are arranged at equal angles from each other. If you visualize a tetraheron(a pyramid with three points on the ground and a fourth point sticking straight up)with the atom centered inside,the four bones will be directed towards the points of the tetrahedron.对于那些有兴趣,实际的骨骼三维硅晶体排列在互相平等的角度。如果你想象tetraheron(金字塔三分,第四个点了起来)的原子为中心的内部,这四个骨头将指向四面体的点。Now we have known our silicon crystal,but we still havent known a semiconductor.In the crystal we saw above,all of the outer electrons of all silicon atoms are used to make covalent bonds with other atoms.There are no electrons available to move from place to place as an electrical current.Thus,a pure silicon crystal is quite a good insulator.In fact,it is almost glass,which is silicon dioxide.A crystal of pure silicon is said to be an intrinsic crystal. To allow our silicon crystal to conduct electricity,we must find a way to allow some electrons to move from place to place within the crystal,in spite of the covalent bonds between atoms.One way to accomplish this is to introduce an impurity such as arsenic or phosphorus into the crystal structure,as shown to the left.These elements are from column Va of the Periodic Table,现在我们已经知道我们的硅晶体,但是我们仍然没有已知的半导体。在上面的水晶我们看到,所有硅原子的外层电子都是用来制造与其他原子共价键。没有可用的电子从一个地方到另一个地方作为电流。因此,纯硅晶体是很好的绝缘体。事实上,它几乎是玻璃,二氧化硅。纯硅的晶体是一种内在的晶体。让我们的硅晶体导电,我们必须找到一种方法,使一些电子转移从一个地方到另一个地方在晶体内,尽管原子之间的共价键。做到这一点的方法之一是引入一个杂质如砷和磷进入晶体结构,如图所示。这些元素是来自弗吉尼亚州列的元素周期表,While this effect is interesting, it still isnt particularly useful by itself. A plain carbon resistor is easier and cheaper to manufacture than a silicon semiconductor one. We still dont have any way to actually control an electrical current.But wait a moment! We obtained a semiconductor material by introducing a 5-electron impurity into a matrix of 4-electron atoms. (For you physics types, were only looking at the outer electrons that are available for bonding-electrons in inner shells are not included in the process or in this discussion.)虽然这种效应是有趣的,但它仍然不是特别有用。纯碳电阻更容易也更便宜比硅半导体制造。我们仍然没有任何方式实际控制电流。但是稍等一下!我们获得了半导体材料通过引入5-electron杂质的矩阵4-electron原子。(你物理类型,我们只看外内层可用于成键电子的不包括在这个过程中或在本讨论。)What happens if we go the other way, and introduce a 3-electron impurity into such a crystal? Suppose we introduce some aluminum (from column a in the Periodic Table) into the crystal, as shown to the left? We could also try gallium, which is also in column a right under aluminum. Now what? These elements only have three electrons available to share with other atoms. Those three electrons do indeed form covalent bonds with adjacent silicon atoms, but the expected fourth bond cannot be formed. A compete connection is impossible here, leaving a “hole” in the structure of the crystal.如果我们去其他方式,引入3-electron杂质进入这样的水晶吗?假设我们介绍一些铝(从列a周期表)晶体,左边所示?我们也可以尝试镓,这也是在正确列a下铝。现在该怎么办呢?这些元素只有三个电子可以与其他原子。这三个电子确实与相邻的硅原子形成共价键,但预期第四债券不能形成。竞争连接是不可能在这里,留下了一个“洞”结构的晶体。Experimentation shows that there is an empty place where an electron should logically go, and often an electron will try to move into that space to fill it. However, the electron filling the hole had to leave a covalent bond behind to fill this empty space, and therefore leaves another hole behind as it moves. Yet another electron may move into that hole, leaving another hole behind, and so forth. In this manner, holes appear to move as positive charges through the crystal. Therefore, this type of semiconductor material is designated “P-type” silicon. By themselves, P-type semiconductors are no more useful than N-type semiconductors.The truly interesting effects begin when the two are combined in various ways. In a single Crystal of silicon.The most basic and obvious combination is a single crystal with an region at one end and a P-type region at the other A crystal with two regions as