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Question
Answer the following giving reasons:
A p-n junction diode is damaged by a strong current.
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Solution
A strong current damages a p-n junction diode because it increases the semiconductor's temperature as more power passes through it and some of that energy is converted to heat. The semiconductor then conducts more current as the temperature rises a little further, which raises the temperature even further. Higher temperature results in more current, which increases the temperature. In what is referred to as a thermal runaway, this cycle keeps repeating. The semiconductor (p-n junction) is ultimately destroyed.
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Consider a box with three terminals on top of it as shown in figure (a):
 (a) |
Three components namely, two germanium diodes and one resistor are connected across these three terminals in some arrangement. A student performs an experiment in which any two of these three terminals are connected in the circuit shown in figure (b).
 (b) |
The student obtains graphs of current-voltage characteristics for unknown combination of components between the two terminals connected in the circuit. The graphs are
(i) when A is positive and B is negative
 (c) |
(ii) when A is negative and B is positive
 (d) |
(iii) When B is negative and C is positive
|
(e) |
(iv) When B is positive and C is negative
 (f) |
(v) When A is positive and C is negative
 (g) |
(vi) When A is negative and C is positive
 (h) |
From these graphs of current-voltage characteristics shown in figure (c) to (h), determine the arrangement of components between A, B and C.
Explain the formation of the barrier potential in a p-n junction.
A semiconductor device is connected in series with a battery, an ammeter and a resistor. A current flows in the circuit. If. the polarity of the battery is reversed, the current in the circuit almost becomes zero. The device is a/an ______.
With reference to a semiconductor diode, define the potential barrier.
