InGaAs-based
Single-Photon Avalanche Diode

Single-Photon Avalanche Diodes (SPADs) are ultra-sensitive photodetectors designed to detect individual photons with exceptional temporal resolution. Unlike conventional photodiodes, SPADs operate in Geiger mode, where the device is biased above its avalanche breakdown voltage.

When a single photon is absorbed in the active region, it generates an electron-hole pair (EHP), which initiates an avalanche multiplication process due to the high electric field. This process leads to a gain factor typically ranging from 10⁵ to 10⁷, allowing even a single photon to produce a large, easily detectable electrical pulse.

InGaAs SPADs offer a superior balance of sensitivity, speed, and integration potential in the 1.0–1.7 μm wavelength range. They are particularly valuable in applications where low-light performance, high timing precision, and long-wavelength response are critical.

Episolution has successfully established a high-performance development pipeline for InGaAs-based single-photon avalanche diodes (SPADs), focusing on material growth, device processing, and characterization. Each step of our process has been carefully engineered to meet the demanding requirements of low-noise, high-sensitivity single-photon detection in the near-infrared range.

Advanced Epitaxial Growth for SPADs
We have enhanced the quality and functionality of SPAD epitaxial layers through precise thickness control and structural optimization. By fine-tuning the guard ring geometry, we have successfully controlled breakdown voltage and boosted avalanche gain, laying the foundation for reliable single-photon detection performance.

Optimized Process Integration
To suppress leakage current and improve signal purity, we have optimized surface passivation techniques through extensive condition tuning. Additionally, Zn diffusion depth and doping concentration have been precisely controlled to enhance avalanche gain while maintaining process stability and reproducibility.

Reliable Device Characterization
We have developed an in-house wafer-level measurement setup tailored for single-photon detector evaluation. This system allows for accurate and repeatable testing of SPAD performance metrics, ensuring a robust feedback loop for continuous improvement and reliable quality control.

We are fully equipped to produce SPAD chips in custom thicknesses ranging from 50 to 200 micrometers, tailored to meet specific customer requirements. Our flexible, precision-driven development process ensures we can deliver optimized solutions for various applications, with a strong commitment to customer satisfaction and collaboration.

InGaAs SPAD technology plays a pivotal role in a wide range of advanced industries and research fields, particularly where high sensitivity and fast timing are critical in the Near Infrared(NIR) spectrum.

• Wavelength Range
  Refers to the range of photon wavelengths that the SPAD can detect effectively. Detection efficiency declines outside this range due to insufficient photon energy (at longer wavelengths) or limited absorption depth (at shorter wavelengths). InGaAs SPADs particularly suitable for detecting photons in the telecommunication window (~1,550 nm), where optical fibers exhibit minimal loss.
• Detection Efficiency (PDE: Photon Detection Efficiency)
  PDE is the probability that an incoming photon is successfully detected by the SPAD. It is calculated as the number of detected photons divided by the number of incident photons.
  In real conditions, false detections (dark counts) occur, so the actual PDE is adjusted as:
  
  
• Dark Count Rate (DCR)
  Represents the number of false detection events per second caused by thermally generated carriers rather than actual photons. A lower DCR improves signal-to-noise ratio, which is especially critical in low-light and quantum applications.
• Timing Jitter
  Measures the temporal precision of photon detection, i.e., the uncertainty in determining the exact arrival time of a photon. Lower jitter enables more accurate time-of-flight measurements and high-resolution temporal imaging.
• Dead Time
  After detecting a photon, the SPAD requires a brief period (called dead time) to reset and become ready for the next event. This duration affects the maximum count rate and is influenced by the quenching circuit design.
• After pulsing
  Occurs when residual trapped carriers from a previous avalanche are released and falsely trigger another detection. Effective gate timing and charge extraction techniques are used to suppress afterpulsing, which is crucial for high-speed or high-count-rate systems.