Silicon Carbide (SiC) is a wide bandgap semiconductor with exceptional material properties that make it highly suitable for demanding sensor applications. Its high thermal conductivity, chemical inertness, and radiation hardness enable operation in extreme environments where conventional semiconductors like silicon fail. Emerging applications include high-temperature gas sensing, radiation detection, and harsh-environment monitoring, leveraging SiC’s unique piezoresistive and optical properties.

### High-Temperature Gas Sensors
Combustion environments, industrial exhaust monitoring, and aerospace propulsion systems require sensors capable of withstanding temperatures exceeding 600°C. SiC-based gas sensors operate reliably in these conditions due to their wide bandgap (3.2 eV for 4H-SiC), which reduces intrinsic carrier generation at high temperatures. Unlike silicon, which becomes conductive at elevated temperatures due to thermal excitation of carriers, SiC maintains stable semiconducting behavior.

Metal-oxide-SiC (MOSiC) and Schottky diode-based gas sensors detect species such as NOx, CO, and hydrocarbons. The MOSiC structure utilizes a catalytic metal oxide layer (e.g., WO3 or TiO2) deposited on SiC, where gas adsorption alters the capacitance or resistance. At high temperatures, the oxide layer enhances selectivity by promoting specific gas-surface interactions. Schottky diodes with Pt or Pd contacts exhibit changes in forward current when exposed to hydrogen due to catalytic dissociation and dipole formation at the interface.

Piezoresistive SiC sensors measure pressure and gas flow in combustion chambers. The piezoresistance effect in SiC is more pronounced at high temperatures compared to silicon, with gauge factors remaining stable up to 800°C. This enables real-time monitoring of exhaust gas dynamics in automotive or turbine engines without signal drift.

### Radiation Detection in Nuclear Facilities
SiC’s radiation hardness and low dark current make it ideal for neutron, gamma-ray, and charged particle detection in nuclear reactors and space environments. The displacement energy of SiC (21–35 eV) is higher than silicon (13 eV), reducing lattice damage under irradiation. SiC-based detectors exhibit stable performance after exposure to fluences exceeding 10^15 neutrons/cm².

Schottky barrier detectors and pn-junction diodes are common configurations. Schottky detectors with thin metal contacts (e.g., Ni or Au) provide high energy resolution for alpha particles due to SiC’s high electron mobility (900 cm²/Vs for 4H-SiC). Pn-junction detectors achieve full depletion at lower voltages because of SiC’s high breakdown field (2–4 MV/cm), enabling compact designs for portable radiation monitors.

Optically stimulated luminescence (OSL) in SiC is used for passive radiation dosimetry. When exposed to ionizing radiation, defects in SiC (e.g., carbon vacancies) trap charge carriers. Subsequent optical excitation releases trapped charges, emitting light proportional to the absorbed dose. This mechanism allows cumulative dose measurement in nuclear facilities without requiring power during exposure.

### Chemical Inertness in Harsh Environments
SiC’s resistance to chemical corrosion enables long-term operation in acidic, alkaline, or oxidizing atmospheres. Unlike metal-oxide sensors that degrade in humid or corrosive gases, SiC sensors maintain functionality in flue gas streams containing SO2 or HCl. The native SiO2 layer on SiC provides additional passivation, preventing surface reactions that would alter sensor response.

### Optical Sensing Mechanisms
SiC’s transparency in the UV to near-infrared range (bandgap-dependent) supports optical gas sensing. UV absorption spectroscopy in SiC waveguides detects gases like O2 and NO2 by measuring attenuation at specific wavelengths. SiC’s high refractive index (2.6–2.7) enhances light-matter interaction, improving sensitivity compared to silica-based sensors.

Photoluminescence (PL) from defects in SiC (e.g., nitrogen-vacancy centers) is exploited for temperature and strain mapping. The PL intensity and peak shift correlate with local stress or temperature gradients, enabling non-contact monitoring of thermal profiles in reactors or electronic devices.

### Comparison of SiC Sensor Technologies

| Sensor Type | Mechanism | Operating Range | Key Advantages |
|----------------------|-------------------------------|-----------------------|------------------------------------|
| MOSiC Gas Sensor | Capacitance/Resistance Change | Up to 1000°C | High selectivity, stable oxides |
| Schottky Gas Sensor | Barrier Height Modulation | Up to 800°C | Fast response, H2 sensitivity |
| Piezoresistive Sensor| Strain-Induced Resistance | Up to 800°C | High gauge factor, dynamic sensing |
| Schottky Radiation | Charge Collection | High radiation fields | Low noise, radiation-hard |
| OSL Dosimeter | Luminescence Release | Cumulative dose | Passive, no power required |

### Future Directions
Research focuses on improving SiC sensor selectivity through nanostructuring and hybrid materials. Porous SiC increases surface area for gas adsorption, while functionalization with graphene or metal-organic frameworks enhances specificity. Integration with wireless readout systems enables distributed sensor networks for industrial process control.

In summary, SiC’s material properties enable robust sensing in extreme conditions, outperforming conventional semiconductors. Its versatility in gas detection, radiation monitoring, and optical sensing ensures growing adoption in aerospace, energy, and safety-critical applications. Advances in fabrication and signal processing will further expand its role in emerging sensor technologies.