Question

A semiconductor $\text{X}$ is made by dropping a germanium crystal with arsenic $(Z=33)$. A second semiconductor $\text{Y}$ is made by doping germanium with indium $(Z=49)$. The two are joined end to end, connected to a battery as shown. Which of the following statements is correct ?

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

Answer 1

The correct option is D $\text{X}$ is $n-$ type and $\text{Y}$ is $p-$ type and the junction is reverse biased.

As germanium crystal (valance electrons=$4$) is doped with arsenic (valance electrons=$5$) to make $\text{X}.$ Thus $\text{X}$ is a $n-$ type semiconductor.

Also, semiconductor $\text{Y}$ is made by doping germanium(valance electrons$=4$) with indium (valance electrons$=3$), hence $\text{Y}$ is a $p-$ type semiconductor.

Now, according to the figure shown, $\text{Y}(p-\text{type})$ is connected to the negative terminal of the battery whereas $\text{X}(n-\text{type})$ is connected to the positive terminal of the battery.

This implies that the junction is reversed biased (by definition of biasing).

Hence, $\left(\text{D}\right)$ is the correct answer.