Pick out the statement which is not correct

Options

A. At a low temperature the resistance of a semiconductor is very high
B. Movement of holes is restricted to the valence band only
C. Width of the depletion region increases as the forward bias voltage increases in case of a N-P junction diode
D. In a forward bias condition, the diode heavily conducts

Explanation

To solve the question, "Pick out the statement which is not correct," we will analyze each of the given options one by one.

### Step 1: Analyze Option 1
**Statement:** At low temperature, the resistance of semiconductor is very high.
**Analysis:** This statement is true. At low temperatures, the thermal energy available to the charge carriers in a semiconductor is low, which results in fewer charge carriers being available to conduct electricity. Therefore, the resistance of the semiconductor is indeed very high at low temperatures.

### Step 2: Analyze Option 2
**Statement:** Moment of holes is restricted to valence band only.
**Analysis:** This statement is also true. Holes are created when electrons jump from the valence band to the conduction band. The movement of holes occurs within the valence band, as they represent the absence of electrons in that band.

### Step 3: Analyze Option 3
**Statement:** Width of the depletion region increases as forward bias voltage increases in case of a NP junction diode.
**Analysis:** This statement is incorrect. When a p-n junction diode is forward-biased, the width of the depletion region actually decreases, not increases. Forward bias reduces the barrier potential, allowing more charge carriers to recombine, which decreases the depletion width.

### Step 4: Analyze Option 4
**Statement:** In a forward bias condition, the diode heavily conducts.
**Analysis:** This statement is true. In forward bias, the diode allows current to flow easily, as the applied voltage reduces the barrier for charge carrier movement.

### Conclusion
After analyzing all the options, we find that **Option 3** is the statement that is not correct.

### Final Answer
**The incorrect statement is Option 3: Width of the depletion region increases as forward bias voltage increases in case of a NP junction diode.**

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