Question

A semiconductor X is made by doping a germanium crystal with arsenic (Z $=$ 33). A second semiconductor Y is made by doping germanium with indium (Z $=$ 49). The two are joined end to end and connected to a battery as shown. 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

Answer 1

Answer: (D)

X is n-type, Y is p-type and the junction is reverse biased

As germanium crystal (group $14$ element) is doped with arsenic, which is a group $15$ element to make $X$. Thus $X$ is a n-type semiconductor.

Also semiconductor $Y$ is made by doping germanium with indium, which is a group $13$ element, hence $Y$ is a p-type semiconductor.

Now according to the figure shown, $Y$ (p-type) is connected to the negative terminal of the battery whereas $X$ (n-type) is connected to the positive terminal of the battery. This implies that the junction is reversed biased (by definition of biasing).