Question

An n-type semiconductor is formed

• A. when germanium crystal is doped with an impurity containing 3 valence electrons
• B. when germanium crystal is doped with an impurity containing 5 valence electrons
• C. from pure germanium
• D. from pure silicon

Answer 1

Answer: (B)

Pentavalent impurity atom i.e., atoms having 5 valence electrons such as antimony (Sb) or arsenic (As), when added to a pure semiconductor, produce excess of free electrons i.e., donor electrons to the semiconductor. For this reason, pentavalent impurity atoms are called donor impurity atom. The semiconductor so produced is called n-type extrinsic semiconductor
So the corresponding wavelength is equal to,
$\lambda =\frac{hc}{E}=\frac{6.67\times 10^{-34}\times 3\times 10^8}{1.5\times 1.6\times 10^{-19}}$
$=8.3375\times 10^{-26}\times 10^{19}=8337.5\mathring{A}$