Carrier lifetime reduction can involve multiple factors, especially in quartz tube application scenarios such as semiconductors, photovoltaics, or high-temperature processes. The main causes include:
1. Quartz Tube Material Issues
- High impurity content: Metallic ions (such as Fe, Cu, Na) or hydroxyl (OH⁻) impurities can form recombination centers, accelerating carrier recombination and reducing lifetime.
- Crystal defects: Structural defects in quartz tubes during manufacturing (such as dislocations and vacancies) may trap carriers, decreasing their effective lifetime.
- Insufficient purity: Synthetic quartz (e.g., high-purity SiO₂) generally offers better carrier lifetime performance than natural quartz. If the supplier’s material purity does not meet the required standard, problems may arise.
2. Process or Environmental Factors
- High-temperature contamination: In high-temperature processes (such as diffusion or annealing), quartz tubes may release impurities or react with process gases (such as O₂, H₂), contaminating wafers or samples.
- Surface contamination: Inadequate cleaning of quartz tubes (residual particles, organic matter) or improper storage (exposure to dust, moisture) can introduce surface recombination centers.
- Thermal stress damage: Rapid heating and cooling can cause microcracks in quartz tubes. Internal stress regions may become active sites for carrier recombination.
3. Testing and Usage Condition Issues
- Mismatch in process parameters: For example, if the temperature exceeds the quartz tube’s tolerance (ordinary quartz tubes may crystallize above 1200°C) or if the gas environment corrodes the tube wall (such as Cl₂, HF).
- Measurement errors: Carrier lifetime testing methods (such as microwave photoconductive decay μ-PCD and quasi-steady-state photoconductance QSSPC) are affected by sample surface condition, light intensity, and other factors, so testing interference must be eliminated.
4. Potential Problems from Other Suppliers
- Deviation in custom specifications: If quartz tube dimensions (such as uneven wall thickness) or coatings (such as anti-reflective coatings) are not optimized to customer requirements, they may cause uneven heat distribution or local defects.
- False labeling of parameters: Some suppliers may falsely claim purity levels (e.g., labeling as “high purity” but actually not reaching 99.99% SiO₂) or fail to disclose hydroxyl content (which affects UV transmittance).
Technical Solutions
- Recommend using low-hydroxyl synthetic quartz tubes to reduce UV absorption and impurity recombination centers.
- Offer custom quartz tube pre-treatment services (such as high-temperature annealing and etching cleaning) to eliminate surface contamination.