Engineering Answers

1. Multiple Choice (Choose the ONE answer that best fits the question/statement.) 

(1) When the “n­factor” of a diode ID = I0(eqV/nkT −1) is 2 at low forward bias voltages, 

what do we suspect? ( ).

A. That the current is dominated by high level injection in the lightly doped, quasi-

neutral region. 

B. That the current is dominated Zener tunneling 

C. That the current is dominated by recombination in the space charge region. 

D. That the current is dominated by generation in the space charge region. 

(2) How does series resistance affect on diode characteristic? ( ). 

A. It leads to the sharp increase of the current 

B. The direct current, depending on the voltage, increases slower than exponential 

law

C. V-I characteristic, starting with the smallest value of voltage, becomes ohmic

D. Negative differential conductance region appears on V-I characteristic of the diode

The excess hole concentration within the quasi-neutral n-type region of a silicon p+n 

step junction of area A = 1mm × 1mm maintained at T = 300K is plotted on a linear 

scale below. The hole lifetime τp = 10-6 s. ni = 1010 cm-3.(1) Calculate the applied voltage, VA. 

(2) Calculate the minority-carrier charge stored in this diode, QP. 

(3) Calculate the diode current, I.

If the slope of the (1/Cdep)2 vs. VA characteristic of a Si PN step junction is 2 × 1023 

F-2V-1, the intercept is 0.84 V, and A is 104 μm2, find the lighter and heavier doping 

concentrations Nl and Nh. 

Compare Ge diodes to similarly structured and doped Si diodes for the following 

(give reasons): 

(1) Reverse saturation current 

(2) Avalanche breakdown voltage

Consider the following nuclear transmutation:²³⁸₉₂U(n,β^-)X. What is the identity of nucleus X?

For the rectangular element considered in Problem 10.52 and Fig. 10.35, find the element nodal force vector when a

concentrated (point) load, with Px0 ¼ 100 N and Py0 ¼ 500 N, act at the point (x0 ¼ 4 cm, y0 ¼ 5 cm). Perform the

needed integration by evaluating the integrand at the centroid of the element and treating the integrand as a constant

throughout the element.

For the rectangular element considered in Problem 10.52 and Fig. 10.35, find the element nodal force vector due to

distributed body force given by fx0 ¼ 0 and fy0 ¼ erg where r is the density of the material and g is the acceleration

due to gravity. Assume the value of r as 2800 kg/m3 and g ¼ 981 m/s2

. Perform the needed integration by evaluating

the integrand at the centroid of the element and treating the integrand as a constant throughout the element

For the rectangular element considered in Problem 10.52 and Fig. 10.35, find the element nodal force vector due to

uniform surface tractions, with Fx0 ¼ 1000 Pa and Fy0 ¼ 500 Pa, applied on the edge (face) ij. Perform the

needed integration by evaluating the integrand at the centroid of the element and treating the integrand as a constant

throughout the element.

For the rectangular element considered in Problem 10.52 and Fig. 10.35, find the element nodal force vector due to

an increase in the temperature of the element by 50 C. Perform the needed integration by evaluating the integrand

at the centroid of the element and treating the integrand as a constant throughout the element. Assume a plane stress

condition for the element

For the element described in Problem 10.36, determine the element nodal force vector as a result of the following prestress: sxx0 ¼ 800 psi, syy0 ¼ 500 psi, and sxy0 ¼ 750 psi. Assume the element to be in a state of plane strain. (take any triangular element or write formula only).