Question

Germanium crystal is doped at room temperature with a minute quantity of boron. The charge carriers in the doped semiconductor will be:

• A. electrons only
• B. holes only
• C. holes and few electrons
• D. electrons and few holes

Hint:

In a p-type semiconductor (e.g., germanium doped with boron), the majority carriers are holes due to acceptor impurities. At room temperature, thermal generation creates a small number of electrons as minority carriers.

Answer 1

The Correct Option is C

Step 1: Identify the type of semiconductor and doping.
Germanium (Ge) is a group IV semiconductor, with 4 valence electrons. Boron (B) is a group III element, with 3 valence electrons. When germanium is doped with boron, boron acts as an acceptor impurity because it has one less valence electron than germanium. Step 2: Determine the type of semiconductor formed.
Since boron has fewer valence electrons, it creates a vacancy (or hole) in the valence band for each boron atom incorporated into the germanium lattice. This makes the doped germanium a p-type semiconductor, where the majority charge carriers are holes. Step 3: Analyze the charge carriers at room temperature.
- In a p-type semiconductor, the majority carriers are holes, created by the acceptor impurities (boron).
- At room temperature, thermal energy can excite some electrons from the valence band to the conduction band, leaving behind holes. This process generates a small number of electron-hole pairs intrinsically. Thus, there will be a few electrons as minority carriers in addition to the majority holes. Step 4: Match with the options.
The charge carriers in the doped germanium are primarily holes (majority carriers) and a few electrons (minority carriers due to thermal generation). This matches option (C).