Which of the following statements is not true?

Options

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

Answer

To solve the question regarding which statement is not true, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Statement 1: The resistance of intrinsic semiconductor decreases with increase of temperature.**
- **Analysis:** In intrinsic semiconductors, as the temperature increases, more electrons gain enough energy to jump from the valence band to the conduction band, creating more charge carriers (electrons and holes). This increase in charge carriers leads to a decrease in resistance. Therefore, this statement is **true**.

2. **Statement 2: Doping pure silicon with trivalent impurities gives p-type semiconductor.**
- **Analysis:** Doping silicon (which is a tetravalent element) with trivalent impurities (like boron or aluminum) creates holes in the crystal structure, resulting in a p-type semiconductor. Thus, this statement is also **true**.

3. **Statement 3: Majority carrier in n-type semiconductor are holes.**
- **Analysis:** In n-type semiconductors, the majority carriers are electrons, not holes. Holes are the majority carriers in p-type semiconductors. Therefore, this statement is **false**.

4. **Statement 4: A PN junction can act as a semiconductor diode.**
- **Analysis:** A PN junction is indeed the fundamental structure of a semiconductor diode, allowing current to flow in one direction while blocking it in the opposite direction. Thus, this statement is **true**.

### Conclusion:
Based on the analysis, the statement that is **not true** is **Statement 3: Majority carrier in n-type semiconductor are holes**.

### Final Answer:
**Statement 3 is not true.**

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