STRUCTURE

The early version of the structure was made by pressing a metal wire onto the surface of a semiconductor. A junction was then formed by passing a pulse of current through the wire and semiconductor. It is believed that doping is diffused from the metal wire as shown in Fig. 1.1(a). Such a structure is referred to as the point contact and the metal wire as a cat’s whisker. (A point contact has the characteristics of either a p-n junction or a Schottky barrier, depending on the forming process. See Section 3.2.) Another old process is the alloy method in which a metal containing the appropriate impurity is placed onto the semiconductor surface. Heating above the eutectic temperature would form an alloy with a thin heavily doped region at the interface. This technique, along with

T

STRUCTURE(b)

FIGURE 1.1

The cross-section structure of a p-n junction as in (a) point contact and (b) planar technology.

STRUCTURE

STRUCTURE

STRUCTURE

FIGURE 1.2

Formation of p-n junction by bringing (a) isolated materials into (b) intimate contact. The potential variation is a result of (c) charge distribution, or (d) field distribution in the depletion layer.

the point contact, is no longer used. A planar structure is shown in Fig. 1.1 (b). The surface doping is usually introduced by ion implantation. Diffusion at high temperature can also be used, and the impurity source can be in a carrying gas or deposited material. A less common technique is to incorporate doping during epitaxial growth. The area of the diode is usually defined by an opening in an insulator layer.

Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *