Download Microelectronic Circuits Quiz 1 for ECE 3040 and more Quizzes Electrical and Electronics Engineering in PDF only on Docsity! ECE 3040 Microelectronic Circuits Quiz 1 May 19, 2004 Professor Leach Name Instructions. Print your name in the space above. The quiz is closed-book, closed-notes, and closed calculator. Honor Code Statement: I have neither given nor received help on this quiz. Initials 1. What determines whether a material is a conductor, a semiconductor, or an insulator? — The number of valence electrons in the outer shell. Conductors have the fewest. Insulators have the most. Semiconductors fall in the middle. 2. Give a brief description of current flow in a metal. — Under the influence of an applied electric field, the free electrons have a force exerted on them which causes them to flow. Collisions cause the average velocity of the electrons to approach a constant, which is called the drift velocity. Thus a constant current flows under the influence of a constant electric field. 3. Why is there no diffusion current in an intrinsic semiconductor? — Because the mobile charge carriers are uniformly distributed. 4. For a conduction current in a conductor, what is meant by “mean free path?” How does it affect the temperature and the electrical resistance of a conductor? — The mean free path is the average distance a mobile charge carrier travels under the influence of an electric field before it collides with a bound atom. The shorter the mean free path, the more collisions charge carriers undergo. This causes the temperature of a conductor to increase and its resistance to increase. 5. What is the direction of the electric field that forms across an open-circuited p-n junction? What is the voltage called that this electric field generates? — It points from the n side to the p side. The voltage is called the built-in voltage. 6. If NA = ND and the mass-action law np = n2i holds, it follows that a doped semiconductor behaves as an intrinsic semiconductor. What fundamental concept is responsible for this conclusion? — The concept of electrical or charge neutrality. That is, if NA = ND and electrical or charge neutrality holds (n +NA = p + ND), it follows that p = n. This is the condition for a semiconductor to be intrinsic. 7. In a semiconductor, it is known that n = n2i / (n+NA). What type semiconductor is it and why? — Electrical or charge neutrality requires n+ NA = p +ND. By the mass-action law, np = n2i . It follows that ND = 0, so the semiconductor is a p-type. 8. What is the basic difference between a conduction or drift current and a diffusion current? — A conduction current consists of the flow of mobile charges (electrons or holes) under the influence of an electric field. A diffusion current is the result of a non-uniform concentration of mobile charges. 1
