Which of the following statements is not true?

Options

A. The resistance of intrinsic semiconductor decreases with increase of temperature.
B. Doping pure Si with trivalent impurities give p-type semiconductor.
C. The majority carriers in n-type semiconductors are holes
D. A p-n junction can act as a semiconductor diode

Answer

To determine which statement is not true regarding semiconductors, we will analyze each statement one by one.

### Step 1: Analyze Statement 1
**Statement 1:** The resistance of intrinsic semiconductor decreases with increase of temperature.

- **Explanation:** In intrinsic semiconductors, as the temperature increases, more charge carriers (electrons and holes) are generated due to thermal excitation. This increase in charge carriers leads to a decrease in resistance.
- **Conclusion:** This statement is **true**.

### Step 2: Analyze Statement 2
**Statement 2:** Doping pure silicon with trivalent impurities gives p-type semiconductor.

- **Explanation:** Trivalent impurities (like Boron) have three valence electrons. When they are added to silicon (which has four valence electrons), they create "holes" because there is one missing electron. These holes act as positive charge carriers, making it a p-type semiconductor.
- **Conclusion:** This statement is **true**.

### Step 3: Analyze Statement 3
**Statement 3:** The majority carriers in n-type semiconductors are holes.

- **Explanation:** N-type semiconductors are doped with pentavalent impurities (like Phosphorus), which have five valence electrons. This results in an excess of electrons, making electrons the majority carriers, not holes.
- **Conclusion:** This statement is **not true**.

### Step 4: Analyze Statement 4
**Statement 4:** A p-n junction acts as a semiconductor diode.

- **Explanation:** A p-n junction is indeed the fundamental structure of a semiconductor diode, allowing current to flow in one direction while blocking it in the opposite direction.
- **Conclusion:** This statement is **true**.

### Final Conclusion
The statement that is **not true** is **Statement 3**: "The majority carriers in n-type semiconductors are holes."