tailieunhanh - Ebook Principles of electronic materials and devices (3rd edition): Part 2

(BQ) The third edition has numerous revisions that include more beautiful illustrations and photographs, additional sections, more solved problems, worked examples, and end-of-chapter problems with direct engineering applications. The revisions have improved the rigor without sacrificing the original semiquantitative approach that both the students and instructors liked and valued. | ó Semiconductor Devices Most diodes are essentially pn junctions fabricated by forming a contact between a p-type and an n-type semiconductor. The junction possesses rectifying properties in that a current in one direction can flow quite easily whereas in the other direction it is limited by a leakage current that is generally very small. A transistor is a three-terminal solid-state device in which a current flowing between two electrodes is controlled by the voltage between the third and one of the other terminals. Transistors are capable of providing current and voltage gains thereby enabling weak signals to be amplified. Transistors can also be used as switches just like electromagnetic relays. Indeed the whole microcomputer industry is based on transistor switches. The majority of the transistors in microelectronics are of essentially two types bipolar junction transistors BJTs and field effect transistors FETs . The appreciation of the underlying principles of the pn junction is essential to understanding the operation of not only the bipolar transistor but also a variety of related devices. The central fundamental concept is the minority carrier injection as purported by William Shockley in his explanations of the transistor operation. Field effect transistors operate on a totally different principle than BJTs. Their characteristics arise from the effect of the applied field on a conducting channel between two terminals. The last two decades have seen enormous advances and developments in optoelectronic and photonic devices which we now take for granted the best examples being light emitting diodes LEDs semiconductor lasers photodetectors and solar cells. Nearly all these devices are based on injunction principles. The present chapter takes the semiconductor concepts developed in Chapter 5 to device level applications from the basic pn junction to heterojunction laser diodes. 475 47Ố CHAPTER 6 Semiconductor Devices IDEAL pn JUNCTION No Applied Bias