Callister - An introduction - 8th edition

18.15 Semiconductor Devices • 749
+
+ +
+
+
p-side
+
+
+
+
Hole flow
+
+
(a)
+
+
+
+ +
–
+ + +
+
+
+
n-side
Recombination zone
Electron flow
Figure 18.21 For a p–n rectifying junction,
representations of electron and hole
distributions for (a) no electrical potential,
(b) forward bias, and (c) reverse bias.
Battery
Hole flow
+
(b)
Electron flow
–
+ +
+ +
– +
+ +
+
+
+
+
Battery
(c)
The current–voltage characteristics for forward bias are shown on the right-hand
half of Figure 18.22.
For reverse bias (Figure 18.21c), both holes and electrons, as majority carriers,
are rapidly drawn away from the junction; this separation of positive and negative
charges (or polarization) leaves the junction region relatively free of mobile charge
carriers. Recombination will not occur to any appreciable extent, so that the junction
is now highly insulative. Figure 18.22 also illustrates the current–voltage behavior
for reverse bias.
Current, I
+
Forward bias
Figure 18.22 The current–voltage
characteristics of a p–n junction for
forward and reverse biases. The
phenomenon of breakdown is also shown.
I F
0
Breakdown
–
–V 0 +
I R +V 0 Voltage, V
Reverse bias
–