Silicon vs. Germanium Photodiodes: A Basic Comparison

If you’ve ever had to choose a photodiode for a project and stared at datasheets until your eyes hurt, you’re not alone. The big question usually boils down to: “Do I go with silicon or germanium?” Both work great, but they’re totally different beasts depending on what light you’re trying to catch. Let’s break it down in plain English—no PhD required.

Why Even Compare Silicon and Germanium?

Silicon photodiodes are everywhere. Your phone camera? Silicon. Most fiber-optic receivers? Silicon. Cheap, tough, super sensitive from about 400 nm to 1100 nm. Germanium, on the other hand, feels a bit more “special ops.” It sees way deeper into the infrared—up to around 1800 nm—so it’s the go-to when you’re working with 1310 nm or 1550 nm telecom wavelengths or doing some night-vision kind of stuff.

Quick look at the wavelength range thing:

Material	Main Sensitivity Range	Peak Responsivity Usually Around	Goes Out To (usable)
Silicon (Si)	400–1100 nm	900–980 nm	~1100 nm
Germanium (Ge)	800–1800 nm	1450–1550 nm	~1850 nm

Yeah, germanium basically laughs at anything past 1100 nm and says “I got you.”

Sensitivity and Quantum Efficiency – Who Wins Where?

Silicon wins hands-down in the visible and near-IR up to 1000 nm. Typical quantum efficiency (QE) for a good Si PIN photodiode is 85–95% around 900 nm. We have some Si PIN Photodiodes at Bee Photon that hit 0.65 A/W at 850 nm without breaking a sweat.

Germanium’s QE peaks lower—usually 70–90% in the 1300–1550 nm region—but that’s still really good for something that can actually see that far. The catch? Germanium has higher dark current (leakage when no light is hitting it), sometimes 10–100× more than silicon at room temperature. That means more noise if you’re doing low-light work without cooling.

Noise and Temperature – The Not-So-Fun Part

Here’s something I learned the hard way on a customer project: germanium dark current doubles roughly every 8–10 °C. Silicon? More like every 15–18 °C. If your detector is going to sit in a box that gets warm, silicon usually behaves better without a thermoelectric cooler.

Real numbers from Hamamatsu and other reputable datasheets (public domain):

Temperature	Typical Si Dark Current (nA)	Typical Ge Dark Current (nA)
25 °C	0.1 – 2	50 – 500
40 °C	~1 – 10	500 – 5000

That’s why a lot of outdoor or industrial applications stick with silicon unless they absolutely need the longer wavelength.

Speed – How Fast Can They React?

Both can be made fast, but silicon PIN structures are easier to make with low capacitance. A 1 mm² Si PIN photodiode can easily give you <1 ns rise time. Germanium is a little slower because the material itself has higher carrier lifetime and capacitance tends to be bigger for the same active area. Typical Ge PIN rise times are 2–10 ns—still blazing fast for most telecom or LIDAR uses, just not quite silicon territory.

Cost Reality Check (2025 prices, roughly)

Tipo	Typical Price (1–99 pcs)	Price per mm² active area
Standard Si PIN (InGaAs no)	$2 – $15	~$3–8
Germanium PIN photodiode	$25 – $120	~$30–100
Cooled InGaAs (if you go even longer)	$200+	Sky’s the limit

Germanium is genuinely 5–20× more expensive than silicon for similar size. If your boss asks “can we use silicon instead?” and you’re only working at 850 nm or 980 nm—the answer is almost always yes, and you’ll save a bundle.

When We Actually Recommend Germanium (Yes, It Happens)

Last year we had a customer doing OCT (optical coherence tomography) at 1300 nm. Silicon was completely blind there. We swapped in a germanium photodiode, noise was higher than they liked, so we added a tiny TEC and a transimpedance amp we designed in-house. End result: 5× better signal-to-noise than their previous silicon attempt. They were grinning ear to ear.

Another fun one: a research lab measuring water vapor absorption lines around 1650 nm. Silicon? Nope. Germanium nailed it on the first try.

Quick Decision Cheat Sheet

Pick Silicon if:

• Your light is 400–1050 nm
• You want low noise without cooling
• Budget matters
• You need super-fast response (<1 ns)

Pick Germanium if:

• You’re working 1200–1800 nm
• You can tolerate (or cool away) higher dark current
• Speed around 2–10 ns is fine
• Money is less of an issue than actually seeing the light

Still unsure? Drop us a line at info@photo-detector.com — we literally do this for a living.

Let’s Put It in a Table One More Time (Because Tables Rule)

Característica	Fotodiodos de silicio	Germanium Photodiodes	Winner for Most People
Wavelength range	400–1100 nm	800–1800 nm	Depends on your λ
Peak responsivity	~0.6–0.7 A/W @ 900 nm	~0.9–1.1 A/W @ 1550 nm	Tie
Dark current (25 °C)	Super low	Noticeably higher	Silicon
Temperature stability	Excelente	Needs cooling above ~35 °C	Silicon
Velocidad	Faster (sub-ns possible)	A bit slower	Silicon
Coste	Cheap	Ouch	Silicon
Availability	Everywhere	Fewer suppliers	Silicon

Real Talk: Is Germanium Ever “Better”?

Better is the wrong word. It’s different. Think of it like camera lenses: a 50 mm prime is cheap and sharp, but if you need to shoot birds 300 m away, you grab the 600 mm telephoto even though it costs ten times more and weighs a ton.

FAQ – Stuff People Actually Ask Us

Still have questions? Want a quote on a custom Si or Ge detector? Hit us up on our página de contacto or just reply to this article. We’re Bee Photon — we build these things every day and love talking shop.

Now go forth and pick the right photodiode without losing your mind staring at datasheets!

— The team at Fotón abeja