In the realm of advanced electronics and photonics, compound semiconductors are the silent enablers of breakthrough performance in many applications. Built from materials like indium gallium arsenide (InGaAs) or gallium arsenide (GaAs), these semiconductors enable applications that are beyond the capabilities of silicon devices.
Examples include avalanche photodiodes (APDs) for ultra-sensitive infrared detection at eye-safe wavelengths. These are used in LiDAR, optical test equipment, optical communications, and laser range finders, for example.
But as useful as they are, APDs made from compound semiconductors have some vulnerabilities, all of which can be mitigated through careful storage, handling, and application. Handle them with care, and you will avoid compromised performance, reduced lifespan, or complete failure.
Here’s what you need to know to ensure these components give their best.
Figure 1 Compound semiconductors have unique characteristics that can lead to vulnerabilities, but all of these can be mitigated with appropriate storage, handling, and application. Source: Phlux Technology
Why compound semiconductors are more fragile than silicon
Compared to silicon, compound semiconductors are physically and chemically more delicate. Their crystal structure makes them brittle, so they’re more likely to crack or chip if dropped or mishandled. Chemically, they’re also more reactive, exposing them to moisture, dust, or skin oils can lead to surface degradation, which affects performance.
They also struggle with heat. Lower thermal conductivity and mismatched coefficients of expansion make them vulnerable to thermal shock. Moreover, poor soldering practices or rapid temperature changes can cause delamination or internal fractures. And because many compound semiconductor APDs operate at low voltages and high impedance, they’re exceptionally sensitive to electrostatic discharge (ESD). A tiny static zap, invisible to you, might silently destroy the device.
APDs: Your handling survival guide
- Watch out for static
ESD isn’t just a nuisance, it’s a silent killer. Always handle APDs in an ESD-safe environment. That includes grounded workbenches, wrist straps, anti-static mats, and maintaining relative humidity between 40–60% to prevent static buildup. Keep the devices in anti-static packaging until you’re ready to use them.
- Handle with a gentle touch
APDs are inherently a little fragile. Use appropriate tools such as tweezers or vacuum pickups and handle the correct areas: the can for TO-CAN packages, the edges for SMDs, and the ferrule (never the fiber) for fiber-pigtailed versions. Never apply pressure to the photosensitive area or exposed wire bonds.
Contamination, whether from skin oils or airborne particles, can degrade signal integrity, so wear gloves and work in cleanroom or semi-clean environments. If cleaning is necessary, use approved solvents or dry nitrogen with extreme care.
- Beware the heat
Thermal stress is one of the top killers of compound semiconductors. Always follow recommended soldering profiles using gradual temperature ramps to prevent cracking or delamination. Preheat boards before reflow soldering and allow cooling to happen slowly. Desoldering is especially risky because temperatures above 330°C, even for just a few seconds, can irreparably damage many APD packages.
- Store them smart
APDs are sensitive even when idle. Store them between 5°C and 30°C, with relative humidity below 60%. Use moisture-barrier bags with desiccant packs and humidity indicators whenever possible. If you remove them from their original packaging, ensure the alternative provides equivalent ESD and moisture protection.
For SMD APDs, pay close attention to their moisture sensitivity level (MSL). Devices stored for extended periods—especially over a year—should be visually inspected and electrically tested before use. And if the MSL safe exposure window has been exceeded, follow proper bake-out procedures before reflow soldering.
Package-specific recommendations
- TO-CAN APDs
These are relatively robust but not invincible. The transparent window is critical for light transmission and must be kept clean and scratch-free. Avoid applying excessive mechanical force to the can, and ensure mounting solutions (sockets, clips, or heat sinks) don’t stress the package. Good thermal management is especially important when operating at high optical power or bias voltage.
Figure 2 Even TO-CAN packaged APDs need careful handling, so it’s important to keep transparent windows clean and scratch-free. Source: Phlux Technology
- SMD APDs
These are compact and efficient, but they come with stricter handling requirements. Many come under MSL 2 or MSL 3 classifications, meaning they must be soldered within a limited time after exposure to air. If that window closes, you’ll need to bake them before soldering. Stick to soldering temperatures between 270–300°C and avoid brief spikes above 330°C.
- Fiber-pigtailed APDs
These versions come with an optical fiber attached, and the fiber is the most delicate part of the assembly. Never bend it below its minimum bend radius and always protect the end-face with a dust cap or ferrule cover. Even minor contamination at the tip can cause significant optical loss or permanent damage.
Best practices summary
- Use strict ESD precautions at every stage of handling.
- Avoid mechanical shocks, bending, or applying pressure in the wrong places.
- Store APDs in controlled temperature and humidity environments with proper packaging.
- Follow soldering guidelines carefully, including reflow and desoldering profiles.
- Keep optical fibers clean and protected from strain or contamination.
APDs built from compound semiconductors are extraordinary components and enablers of much of the technology we take for granted today. However, they also require more attention than their silicon-based cousins. If you handle them with the precision they deserve, you’ll be rewarded with reliable, high-quality results.
If not, the damage might not show up immediately but rear its head later. Handle with care to reap the full benefits of these devices, including those of the world’s most sensitive 1550-nm noiseless InGaAs APD sensors.
Christian Rookes is VP of marketing at Phlux Technology, a manufacturer of avalanche photodiode (APD) infrared sensors based in Sheffield, UK. He has over 25 years’ experience in technical marketing in semiconductors and optical communications. He holds two patents, including one related to impedance matching for laser diode circuits.
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