Question

A semi-conductor $X$ is made by doping a germanium crystal with arsenic ($Z=33$). A second semi-conductor $Y$ 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

The correct option is D $X$ is $n-$type, $Y$ is $p-$type and the junction is reverse biased.

As the arsenic is a pentavalent atom so it is a n-type material and indium is a trivalent atom so it is a p-type material. Therefore, X is a n-type and Y is a p-type semiconductors.
Forward biased means that positive end of the battery is connected to the p-type semiconductor and the negative end of the battery is connected to the the n-type semiconductor.
Reverse biased diode means that positive end of the battery is connected to the n-type semiconductor and the negative end of the battery is connected to the the p-type semiconductor.
So given p-n junction in reverse biased.