Optoelectronics — dark current definition: Is “dark current” the small reverse current that flows in a photodiode when it receives no incident light?

Introduction / Context:
Photodiodes convert light to current. Even in the absence of light, a small reverse leakage known as dark current flows due to thermally generated carriers and junction leakage. Recognizing dark current is essential for low-light detection, noise budgeting, and precision optical measurements.

Given Data / Assumptions:

• Photodiode operated in reverse bias (photoconductive mode).
• No optical input (dark condition).
• Temperature within normal operating range unless otherwise specified.

Concept / Approach:
Dark current sets the baseline noise floor and limits the smallest detectable signal. It arises primarily from generation–recombination processes within the depletion region, surface leakage, and thermal effects. While the magnitude depends on device design and temperature, the definition remains constant: dark current is the reverse current present with zero illumination.

Step-by-Step Solution:

Verification / Alternative check:
Measure current as a function of temperature in the dark; dark current typically increases with temperature, confirming its thermal origin. Introducing controlled light above this baseline adds photocurrent linearly (for small-signal regions), validating the separation between dark current and signal current.

Why Other Options Are Wrong:
Limiting to high temperature, avalanche-only, or forward bias is incorrect. Although temperature strongly affects magnitude, the definition does not change; forward bias is not the normal detection mode for photodiodes.

Common Pitfalls:
Misinterpreting dark current as measurement offset error; failing to account for it leads to inflated sensitivity claims.

Final Answer:
Correct