Let%27s delve into the fascinating world of hot-carrier effects in MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors):

1. Definition and Physics:
- Hot-carrier injection (HCI) occurs in solid-state electronic devices when an electron or a "hole" gains sufficient kinetic energy to overcome a potential barrier, allowing it to break an interface state.
- The term "hot" refers to the effective temperature used to model carrier density, not the overall device temperature.
- In MOSFETs, hot carriers are injected from the conducting channel in the silicon substrate to the gate dielectric (usually silicon dioxide, SiO₂).
- To become "hot," an electron must gain a kinetic energy of approximately 3.2 eV, while holes require 4.6 eV to enter the conduction band of SiO₂.
- The term "hot electron" describes non-equilibrium electrons (or holes) in semiconductors, characterized by elevated effective temperatures.

2. Effects and Consequences:
- Hot electrons can tunnel out of the semiconductor material, rather than recombining with a hole or being conducted to a collector.
- Consequences include:
- Increased Leakage Current: Hot carriers disrupt the atomic structure of the gate dielectric, leading to leakage.
- Device Degradation: Trapped hot carriers can form a space charge, causing instability or degradation.
- Energy Dissipation: In some devices (e.g., solar cells), hot electron phonons dissipate energy inefficiently as heat.
- Atomic Structure Alteration: Hot carriers can rupture stable Si-H bonds, affecting MOSFET parameters.

3. Generation of Hot Electrons:
- High-energy photons (e.g., light) striking a semiconductor can transfer energy to an electron, creating an electron-hole pair.
- If the electron gains enough energy to surpass the conduction band, it becomes a hot electron.
- These high-energy carriers are very mobile and can leave the semiconductor, affecting neighboring materials.

4. Substrate Biasing and HCI:
- Substrate biasing can mitigate hot-carrier effects.
- By adjusting the substrate voltage, we influence the threshold voltage and leakage current.
- However, at smaller process nodes, the impact of substrate biasing diminishes.

In summary, hot-carrier effects are critical considerations in MOSFET design. Engineers balance performance and reliability while managing these energetic carriers.


(1) Hot-carrier injection - Wikipedia. https://en.wikipedia.org/wiki/Hot-carrier_injection.
(2) Hot Carriers; Hot Electrons - eesemi.com. https://eesemi.com/hotcarriers.htm.
(3) MOSFET Small-Signal Model Considering Hot-Carrier Effect for Millimeter .... https://link.springer.com/article/10.1007/s10762-019-00574-4.
(4) Hot Electron effect in mosfet - Siliconvlsi. https://siliconvlsi.com/hot-electron-effect-in-mosfet/.

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