2013秋专业英研究生试卷

学生姓名__________ 学号_________________专业___________导师姓名 ______________

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烟台大学硕士研究生20 13 ～20 14 学年第 1 学期

Consider a Pb-Sn solder that is 38.1wt% Pb and 61.9wt% Sn (this is the eutectic composition with the lowest melting point). What are the atomic fractions of Pb and Sn in this solder? Given MPb=207.2 and MSn=118.71.

Problem 2 (resistivity of intrinsic and doped Si. 20 points)

Find the resistance of a 1 cm3 pure silicon crystal cube. What is the resistance when the crystal is doped with arsenic (As) if the doping is 1 in 109, that is, 1 part per billion (ppb) (note that this doping corresponds to one foreigner living in China)? Given data: atomic concentration in silicon is 5 1022cm-3, ni=1.0 1010cm-3, e=1350cm2V-1s-1, and h=450cm2V-1s-1. If doping with boron instead of arsenic (a p-type semiconductor with the same level of doping.

a. A 50g golf ball traveling at a velocity of 20ms-1.

b. A proton traveling at 2200mS-1. Given mp=1.67 10-27kg.

c. An electron accelerated by 100V. Given me=9.10938188 × 10-31. Consider two copper wires separate only by their surface oxide layer (CuO). Classically, since the oxide layer is an insulator, no current should be possible through the two copper wires. Suppose that for the conduction (“free”) electrons in copper, the surface oxide layer looks like a square potential energy barrier of height 10eV. Consider an oxide layer thickness of 5 nm and evaluate the transmission coefficient for conduction electrons in copper, which have a kinetic energy of about 7 eV. What will be the transmission coefficient if the oxide barrier is 1 nm?

Problem 5 (Noise in RLC circuit. 10 points)