Which of the following statements is not true?

Options

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

Answer

To solve the question "Which of the following statements is not true?" regarding semiconductor devices, we will analyze each statement provided in the options systematically.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- **Statement:** "The resistance of intrinsic semiconductors decreases with increase of temperature."
- **Explanation:** In intrinsic semiconductors, as the temperature increases, more electrons gain enough energy to jump from the valence band to the conduction band. This leads to an increase in the number of charge carriers (electrons), which in turn increases conductivity and decreases resistance.
- **Conclusion:** This statement is **true**.

2. **Analyze the Second Statement:**
- **Statement:** "Doping pure semiconductor or silicon with trivalent impurity gives p-type semiconductors."
- **Explanation:** Doping silicon (which has four valence electrons) with a trivalent impurity (like boron or aluminum, which has three valence electrons) creates "holes" in the crystal structure where an electron is missing. These holes act as positive charge carriers, leading to the formation of a p-type semiconductor.
- **Conclusion:** This statement is **true**.

3. **Analyze the Third Statement:**
- **Statement:** "The majority charge carriers in n-type semiconductor are holes."
- **Explanation:** In n-type semiconductors, silicon is doped with a pentavalent impurity (like phosphorus), which has five valence electrons. This results in an excess of electrons, making electrons the majority charge carriers, while holes are the minority carriers.
- **Conclusion:** This statement is **false**.

4. **Analyze the Fourth Statement:**
- **Statement:** "A p-n junction can act as a semiconductor diode."
- **Explanation:** A p-n junction is the fundamental structure of a semiconductor diode. It allows current to flow in one direction while blocking it in the opposite direction, which is the defining characteristic of a diode.
- **Conclusion:** This statement is **true**.

### Final Conclusion:
The statement that is **not true** is the third statement: "The majority charge carriers in n-type semiconductor are holes." Therefore, the answer to the question is that the third statement is false.