Question

A wafer of pure germanium crystal has two parts X and Y. The end X is obtained by doping with arsenic and Y with indium. It is connected to a battery as shown in the figure. Which of the following statements is correct?

• A. X is p-type, Y is n-type and the junction is forward biased
• B. X is n-type, Y is p-type and the junction is forward biased
• C. X is p-type, Y is n-type and the junction is reverse biased
• D. X is n-type, Y is p-type and the junction is reverse biased

Hint:

To remember doping types easily:
- Group 1\textbf{5} (\textbf{P}entavalent) \(\rightarrow\) \textbf{N}-type (\textbf{P}lenty of electrons).
- Group 1\textbf{3} (\textbf{T}rivalent) \(\rightarrow\) \textbf{P}-type (\textbf{P}ositive holes).
For biasing, remember \textbf{P}ositive to \textbf{P}-type is \textbf{F}orward bias.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The goal of this question is to identify the type of semiconductor formed in each region (X and Y) based on the dopants used and then determine the biasing condition of the resulting p-n junction from the provided circuit diagram.
Step 3: Detailed Explanation:
1. Identification of Semiconductor Types:
- Pure Germanium (Ge) belongs to Group 14 of the periodic table.
- Part X: This part is doped with Arsenic (As). Arsenic is a Group 15 element, which means it has 5 valence electrons (pentavalent impurity). When a pentavalent impurity is added to a tetravalent semiconductor like Ge, it provides an extra free electron, creating an n-type semiconductor.
- Part Y: This part is doped with Indium (In). Indium is a Group 13 element, which has 3 valence electrons (trivalent impurity). When a trivalent impurity is added to Ge, it creates a vacancy or "hole," resulting in a p-type semiconductor.
2. Biasing Analysis:
- In the provided diagram, a battery is connected to the X-Y block.
- The longer vertical line of the battery symbol represents the positive terminal, and the shorter, thicker line represents the negative terminal.
- Region X (n-type) is connected to the negative terminal.
- Region Y (p-type) is connected to the positive terminal.
- When the p-type region is connected to the positive terminal and the n-type region is connected to the negative terminal of an external source, the junction is said to be forward biased.
Step 4: Final Answer:
Region X is n-type, region Y is p-type, and the configuration is forward biased. This matches statement (B).