Semiconductor Doping and P-N Junction Formation

Introduction:
Doping is the process of intentionally introducing impurities into a semiconductor material to modify its electrical properties. By doping a semiconductor, we can create an excess of either electrons (n-type) or holes (p-type) in the material, which allows for the formation of a P-N junction.

Germanium:
Germanium is a semiconductor material that is commonly used in electronic devices. It has four valence electrons, meaning it can form covalent bonds with its neighboring atoms. Germanium is an intrinsic semiconductor, which means its electrical conductivity is low at room temperature.

P-N Junction Formation:
A P-N junction is formed when a p-type semiconductor (excess holes) is brought in contact with an n-type semiconductor (excess electrons). This combination creates a region with a high concentration of positive and negative charges, leading to the formation of a depletion region.

Doping:
In order to create a P-N junction in germanium, we need to dope it with specific impurities. Doping involves adding impurities to the semiconductor material, which changes its electrical conductivity.

Gallium and Phosphorus Doping:
In the given options, the correct answer is option 'D', which states that gallium and phosphorus are doped into germanium to form a P-N junction.

- Gallium is a group III element and has three valence electrons. When it is doped into germanium, it acts as a p-type dopant by replacing some of the germanium atoms in the crystal lattice. Gallium donates its three valence electrons, creating an excess of holes in the material.

- Phosphorus is a group V element and has five valence electrons. When it is doped into germanium, it acts as an n-type dopant by replacing some of the germanium atoms. Phosphorus brings an extra electron to the crystal lattice, creating an excess of electrons in the material.

P-N Junction Formation:
When gallium-doped germanium (p-type) and phosphorus-doped germanium (n-type) are brought in contact, a P-N junction is formed. The excess electrons from the n-type region diffuse towards the p-type region, while the excess holes from the p-type region diffuse towards the n-type region. This diffusion process creates a depletion region at the junction, which is devoid of any charge carriers.

Conclusion:
In summary, by doping gallium and phosphorus into germanium, we can create a P-N junction. The gallium doping introduces excess holes, making the material p-type, while the phosphorus doping introduces excess electrons, making the material n-type. When these two doped materials are brought together, a P-N junction is formed, enabling various applications in electronic devices.