TEST BANK FOR Electronic Devices and Circuit Theory 10thed By Robert L.Boylestead By Louis Nashelsky

1. Copper has 20 orbiting electrons with only one electron in the outermost shell. The fact that
the outermost shell with its 29th electron is incomplete (subshell can contain 2 electrons) and
distant from the nucleus reveals that this electron is loosely bound to its parent atom. The
application of an external electric field of the correct polarity can easily draw this loosely
bound electron from its atomic structure for conduction.
Both intrinsic silicon and germanium have complete outer shells due to the sharing (covalent
bonding) of electrons between atoms. Electrons that are part of a complete shell structure
require increased levels of applied attractive forces to be removed from their parent atom.
2. Intrinsic material: an intrinsic semiconductor is one that has been refined to be as pure as
physically possible. That is, one with the fewest possible number of impurities.
Negative temperature coefficient: materials with negative temperature coefficients have
decreasing resistance levels as the temperature increases.
Covalent bonding: covalent bonding is the sharing of electrons between neighboring atoms to
form complete outermost shells and a more stable lattice structure.
3. −
4. W = QV = (6 C)(3 V) = 18 J
5. 48 eV = 48(1.6 × 10−19 J) = 76.8 × 10−19 J
Q = W
V
=
76.8 10 19 J
12 V
× −
= 6.40 × 10−19 C
6.4 × 10−19 C is the charge associated with 4 electrons.
6. GaP Gallium Phosphide Eg = 2.24 eV
ZnS Zinc Sulfide Eg = 3.67 eV
7. An n-type semiconductor material has an excess of electrons for conduction established by
doping an intrinsic material with donor atoms having more valence electrons than needed to
establish the covalent bonding. The majority carrier is the electron while the minority carrier
is the hole.
A p-type semiconductor material is formed by doping an intrinsic material with acceptor
atoms having an insufficient number of electrons in the valence shell to complete the covalent
bonding thereby creating a hole in the covalent structure. The majority carrier is the hole
while the minority carrier is the electron.
8. A donor atom has five electrons in its outermost valence shell while an acceptor atom has
only 3 electrons in the valence shell.
9. Majority carriers are those carriers of a material that far exceed the number of any other
carriers in the material.
Minority carriers are those carriers of a material that are less in number than any other carrier
of the material.
2
10. Same basic appearance as Fig. 1.7 since arsenic also has 5 valence electrons (pentavalent).
11. Same basic appearance as Fig. 1.9 since boron also has 3 valence electrons (trivalent).
12. −
13. −
14. For forward bias, the positive potential is applied to the p-type material and the negative
potential to the n-type material.
15. TK = 20 + 273 = 293
k = 11,600/n = 11,600/2 (low value of VD) = 5800
ID = Is 1
D
K
kV
e T
⎛ ⎞
⎜⎜ − ⎟⎟
⎝ ⎠
= 50 × 10−9
(5800)(0.6)
e 293 1
⎛ ⎞
⎜ − ⎟
⎝ ⎠
= 50 × 10−9 (e11.877 − 1) = 7.197 mA
16. k = 11,600/n = 11,600/2 = 5800 (n = 2 for VD = 0.6 V)
TK = TC + 273 = 100 + 273 = 373
(5800)(0.6 V)
ekV /TK = e 373 = e9.33 = 11.27 × 103
I = ( kV /TK 1)
s I e − = 5 μA(11.27 × 103 − 1) = 56.35 mA
17. (a) TK = 20 + 273 = 293
k = 11,600/n = 11,600/2 = 5800
ID
= Is 1
D
K
kV
e T
⎛ ⎞
⎜⎜ − ⎟⎟
⎝ ⎠
= 0.1μA
(5800)( 10 V)
e 293 1
⎛ − ⎞
⎜ − ⎟
⎝ ⎠
= 0.1 × 10−6(e−197.95 − 1) = 0.1 × 10−6(1.07 × 10−86 − 1)
≅ 0.1 × 10−6 0.1μA
ID = Is = 0.1 μA
(b) The result is expected since the diode current under reverse-bias conditions should equal
the saturation value.
18. (a)
x y = ex
0 1
1 2.7182
2 7.389
3 20.086
4 54.6
5 148.4
(b) y = e0 = 1
(c) For V = 0 V, e0 = 1 and I = Is(1 − 1) = 0 mA
3
19. T = 20°C: Is = 0.1 μA
T = 30°C: Is = 2(0.1 μA) = 0.2 μA (Doubles every 10°C rise in temperature)
T = 40°C: Is = 2(0.2 μA) = 0.4 μA
T = 50°C: Is = 2(0.4 μA) = 0.8 μA
T = 60°C: Is = 2(0.8 μA) = 1.6 μA
1.6 μA: 0.1 μA ⇒ 16:1 increase due to rise in temperature of 40°C.
20. For most applications the silicon diode is the device of choice due to its higher temperature
capability. Ge typically has a working limit of about 85 degrees centigrade while Si can be
used at temperatures approaching 200 degrees centigrade. Silicon diodes also have a higher
current handling capability. Germanium diodes are the better device for some RF small signal
applications, where the smaller threshold voltage may prove advantageous.
21. From 1.19:
−75°C 25°C 125°C
VF
@ 10 mA
Is
1.1 V
0.01 pA
0.85 V
1 pA
0.6 V
1.05 μA
VF decreased with increase in temperature
1.1 V: 0.6 V ≅ 1.83:1
Is increased with increase in temperature
1.05 μA: 0.01 pA = 105 × 103:1
22. An “ideal” device or system is one that has the characteristics we would prefer to have when
using a device or system in a practical application. Usually, however, technology only
permits a close replica of the desired characteristics. The “ideal” characteristics provide an
excellent basis for comparison with the actual device characteristics permitting an estimate of
how well the device or system will perform. On occasion, the “ideal” device or system can be
assumed to obtain a good estimate of the overall response of the design. When assuming an
“ideal” device or system there is no regard for component or manufacturing tolerances or any
variation from device to device of a particular lot.
23. In the forward-bias region the 0 V drop across the diode at any level of current results in a
resistance level of zero ohms – the “on” state – conduction is established. In the reverse-bias
region the zero current level at any reverse-bias voltage assures a very high resistance level −
the open circuit or “off” state − conduction is interrupted.
24. The most important difference between the characteristics of a diode and a simple switch is
that the switch, being mechanical, is capable of conducting current in either direction while
the diode only allows charge to flow through the element in one direction (specifically the
direction defined by the arrow of the symbol using conventional current flow).