Session 7 The pn Junction（Ⅰ）

7.1 Introduction

Most semiconductor devicescontain at least one junction between p-type and n-type semiconductor regions. Semiconductor device characteristics and operation are intimately connected to these pn junctions，so considerable attention is devoted initially to this basic device. The pn junction diodeitself provides characteristics that are used in rectifiersand switching circuits . In addition，the analysis of the pn junction device establishes some basic terminology and concepts that are used in the discussion of other semiconductor devices. The fundamental analysis techniques used for the pn junction will also be applied to other devices. Understanding the physics of the pn junction is，therefore，an important step in the study of semiconductor devices.

The pn junction must not contain more than a small number of imperfection. In practice this means either that the device has been made from a slice cut from a large single crystal，parts of which have been transformed by diffusing or ion-implanting doping atoms from the surface，or that new material has been grown epitaxially to extend a crystal substrate and to allow the including of a pn junction.