Photodiodes are semiconductor devices that convert optical signals into electrical currents. Operating under reverse bias voltage, they generate electron-hole pairs when exposed to light, enabling precise light intensity measurement. As critical components in optoelectronics, photodiodes enable applications ranging from industrial automation to medical diagnostics, offering advantages like fast response times, high reliability, and compatibility with digital systems.
| Type | Functional Characteristics | Application Examples |
|---|---|---|
| PIN Photodiode | Wide depletion region for high quantum efficiency | High-speed optical communication (e.g., 10Gbps fiber links) |
| Avalanche Photodiode (APD) | Internal gain through impact ionization | LIDAR systems, single-photon detection |
| Schottky Photodiode | Low capacitance for fast switching | UV radiation monitoring in semiconductor manufacturing |
| Metal-Semiconductor-Metal (MSM) | Planar structure for high-frequency operation | Optical interconnects in data centers |
| UV Photodiode | Spectral sensitivity below 400nm | Flame detection systems, water purification monitoring |
Photodiodes typically consist of a p-n junction or p-i-n structure fabricated from silicon, germanium, or indium gallium arsenide (InGaAs). The core components include: (1) Light-receiving window with anti-reflective coating, (2) Active semiconductor layer for photon absorption, (3) Electrodes (anode/cathode) for current collection, (4) Ceramic or plastic package with optical filter integration. Advanced designs incorporate micro-lenses and back-illuminated structures to enhance quantum efficiency.
| Parameter | Description | Importance |
|---|---|---|
| Responsivity (A/W) | Current output per unit optical power | Determines signal strength at given irradiance |
| Dark Current (nA) | Leakage current without illumination | Impacts signal-to-noise ratio in low-light conditions |
| Rise Time (ns) | Response speed to intensity changes | Critical for high-frequency modulation applications |
| Junction Capacitance (pF) | Parasitic capacitance at depletion region | Limits bandwidth in transimpedance amplifier circuits |
| Spectral Response Range (nm) | Effective wavelength detection window | Dictates compatibility with light sources (e.g., 850nm VCSELs) |
| Manufacturer | Representative Product | Key Features |
|---|---|---|
| Hamamatsu Photonics | S1223-6BQ | High-speed Si photodiode with 1.3GHz bandwidth |
| OSRAM Opto | BFW21R | Blue-enhanced PIN diode for LiDAR applications |
| First Sensor | FDS030 | Low-noise APD for single-photon counting |
| Excelitas Technologies | C30655GH | InGaAs photodiode for 1.55 m telecom wavelengths |
| Vishay Semiconductors | BPW34S | High-radiation hardness for industrial sensors |
Key considerations include: (1) Spectral matching with light source (e.g., InGaAs for 1550nm fiber systems), (2) Response time requirements (PIN vs APD tradeoffs), (3) Operating temperature range (-40 C to +85 C industrial grade), (4) Packaging constraints (SMD vs through-hole), and (5) Cost vs performance optimization (e.g., APDs require bias voltage regulators).
Current development focuses on: (1) Graphene-based photodiodes for THz imaging, (2) CMOS-integrated single-photon avalanche diodes (SPADs) for LiDAR, (3) Flexible organic photodiodes for wearable devices, (4) Quantum dot photodiodes for extended IR sensitivity, and (5) AI-driven smart sensors with on-chip signal processing. Market growth is projected at 7.2% CAGR through 2028, driven by 5G optical networks and autonomous vehicle sensing systems.
