PIN diode structure identification — doping profile and intrinsic region Which option correctly describes the doping of a PIN diode's terminals relative to its intrinsic (i) region?
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Ap+ and n layers separated by i layer
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Bp+ and n+ layers separated by i layer
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Cp- and n- layers separated by i layer
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Dnone of the above
Answer
Correct Answer: p+ and n+ layers separated by i layer
Explanation
Introduction / Context:PIN diodes are essential RF/microwave control elements acting as current-controlled resistors at high frequency. Their behavior arises from a specific layer structure that enables charge storage in the intrinsic region, giving a nearly resistive RF impedance under forward bias and high impedance under reverse bias.
Given Data / Assumptions:
- Device under test: PIN diode.
- Asked: which doping configuration is correct around the intrinsic layer.
Concept / Approach:A PIN diode consists of a heavily doped p-type region (p+), an intrinsic (undoped or very lightly doped) region (i), and a heavily doped n-type region (n+). The heavy doping lowers series resistance and facilitates charge injection; the i-region stores charge, yielding a controllable RF resistance with bias current.
Step-by-Step Solution:
1) Identify intrinsic layer at the center: symbol ‘‘i’’.2) Heavily dope both ends: p+ and n+ to reduce series resistance.3) Therefore the correct description is p+ – i – n+.Verification / Alternative check:Equivalent-circuit models and datasheets emphasize the low series resistance due to heavy terminal doping and the bias-dependent resistance from the stored charge in the i-region.
Why Other Options Are Wrong:
- p+ and n (lightly doped n): not the standard PIN structure.
- p- and n-: incorrectly suggests lightly doped terminals; would raise series resistance.
- None of the above: incorrect because p+ – i – n+ is standard.
Common Pitfalls:Confusing PIN with ordinary PN junction; overlooking the role of the intrinsic region in RF behavior.
Final Answer:p+ and n+ layers separated by i layer