Silicon is mostly chosen over germanium due to its greater working temperature. Let's understand why:

1. Working Temperature: Silicon has a higher working temperature compared to germanium. This means silicon-based devices can operate at higher temperatures without experiencing significant degradation in performance or reliability. Germanium, on the other hand, has a lower maximum operating temperature, making it less suitable for applications that involve high-temperature environments.

2. Thermal Stability: Silicon exhibits better thermal stability than germanium. It can withstand higher levels of thermal stress without undergoing significant changes in its electrical properties. This makes silicon-based devices more reliable and less prone to failure due to temperature fluctuations.

3. Bandgap: The bandgap of silicon is larger than that of germanium. The bandgap determines the energy required for an electron to move from the valence band to the conduction band, allowing the material to conduct electricity. A larger bandgap means silicon requires higher energy levels to conduct, making it suitable for high-temperature applications. Germanium, with its smaller bandgap, is more suitable for low-temperature applications.

4. Power Consumption: While silicon generally has lower power consumption compared to germanium, this factor is not the primary reason for choosing silicon over germanium. Both materials can be used to design low-power devices, but silicon's other advantages, such as working temperature and thermal stability, make it a more preferred choice.

5. Large ICBO: ICBO (Collector Current Base-Open Circuit) is a parameter that represents the leakage current flowing between the collector and base terminals when the emitter is left open. While germanium transistors generally exhibit lower ICBO values compared to silicon transistors, this is not a significant factor in choosing silicon over germanium. ICBO values can be controlled through proper design techniques and are not the main reason for the preference of silicon.

In conclusion, silicon is mostly chosen over germanium due to its greater working temperature, better thermal stability, and larger bandgap. These properties make silicon more suitable for high-temperature applications and ensure the reliability and performance of silicon-based devices even under challenging operating conditions.