Semiconductor choice for varactor (varicap) diodes: which materials are commonly used?

Introduction:
Varactor (varicap) diodes exploit the voltage-dependent junction capacitance of a reverse-biased p–n junction for tuning oscillators, filters, and frequency multipliers. Material choice affects Q factor, capacitance ratio (Cmax/Cmin), breakdown, and frequency performance.

Given Data / Assumptions:

• Reverse-biased junction operated in the depletion region.
• Goal is tunable capacitance with low series resistance and adequate breakdown voltage.
• High-frequency (RF to microwave) operation is typical.

Concept / Approach:

Silicon varactors are widely used for RF tuning because Si technology offers mature processing, good Q, and cost efficiency. Gallium arsenide (GaAs) varactors are preferred at higher microwave/millimeter-wave frequencies due to superior electron mobility and lower series resistance, enabling higher Q and lower loss at very high frequencies. Both materials appear in commercial varactor families depending on the target band and performance trade-offs.

Step-by-Step Solution:

Verification / Alternative check:

Microwave components catalogs list Si hyperabrupt varactors for VCOs and GaAs planar varactors for mm-wave multipliers—evidence that both materials are standard choices.

Why Other Options Are Wrong:

• Only Si or only GaAs: too restrictive.
• Neither Si nor GaAs / only Ge: inconsistent with mainstream device technology.

Common Pitfalls:

Assuming one material universally dominates; selection is application-specific and frequency-dependent.

Final Answer:

either silicon or GaAs