A semiconductor `X` is made by dopping a germanium crystal with arsenic `(Z=33)`. A scond semiconductor `Y` is made by dopping 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?

Options

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

D

Explanation

Arsenic has five valence electrons, so it a donor impurity. Hence `X` becomes `N`-type semiconductor. Indium has only three outer electrons, so it is an acceptor impurity. Hence `Y` becomes `P`-type semiconductor. Also `N` (i.e,. `X`) is connected to positive terminal of battery and `P(i.e. Y)` is connected to negative terminal of battery so `PN`-junction is reverse biased.