Question:
The Forbidden Energy Gap for Germanium is:
- 1.5 eV
- 1.1 eV
- 1.27 eV
- 0.72 eV
Answer:
The correct option is(4).
The Forbidden Energy Gap for Germanium is 0.72 eV. The term “forbidden energy gap” in semiconductors refers to the energy range between the valence band and the conduction band where no electron states can exist. For germanium, this gap is approximately 0.72 electron volts (eV). This gap is crucial in defining the semiconductor’s electrical and optical properties.
Explanation:
Here’s a detailed explanation of what this means and why it’s important:
- Energy Bands in Semiconductors: In semiconductors, the electrons are organized into bands:
- Valence Band: This is the highest energy band that is fully occupied by electrons at absolute zero temperature. Electrons in this band are involved in bonding the material together and do not contribute to electrical conductivity under normal circumstances.
- Conduction Band: This is the higher energy band above the valence band. It is mostly empty at zero temperature. Electrons in this band are free to move within the material, contributing to its electrical conductivity.
- Forbidden Energy Gap: The gap between the valence band and the conduction band is called the “forbidden gap” or “band gap.” No electron states exist in this gap, meaning electrons cannot possess energies within this range under normal conditions.
- Significance of the Band Gap (0.72 eV for Germanium):
- Determines Electrical Conductivity: The size of the band gap is critical in determining a material’s electrical properties. For germanium, the band gap of 0.72 eV means that a relatively small amount of energy (such as thermal energy at room temperature) is sufficient to excite electrons from the valence band into the conduction band. This makes germanium a good semiconductor because it can effectively conduct electricity when doped or when energy is supplied.
- Temperature Dependence: As temperature increases, more electrons gain enough energy to jump across the band gap from the valence to the conduction band, enhancing conductivity.
- Comparison with Other Semiconductors: For instance, silicon has a band gap of about 1.1 eV, which is larger than that of germanium. This difference makes silicon less conductive at room temperature than germanium but gives it better thermal stability and makes it more suitable for high-temperature applications.
The band gap of 0.72 eV in germanium is crucial for applications where low band gap and high intrinsic conductivity at room temperature are desirable, such as in infrared detectors and other semiconductor devices operating at lower energy thresholds.