Hey there, if you’ve ever worked with Schottky diodes long enough, you’ve probably heard the word “reverse bias stress” thrown around like it’s some kind of dark magic that’ll turn your diode into a paperweight. As a Schottky diode supplier that’s been around the block (we’ve shipped parts to everyone from small startup labs to aerospace engineering teams, so trust me on this), I get why this stuff can feel confusing. A lot of folks reach out to us panicking because their diodes are failing under reverse bias and they can’t figure out if it’s a part issue, an application issue, or just how these things work under pressure. Let’s break this down like we’re chatting over a coffee (skip the fancy lab jargon where we can, but I’ll keep it accurate because that’s why you’re here). Schottky Diode
First, let’s recap what a Schottky diode is, real quick, because if you skip this, reverse bias stress won’t make any sense. Unlike regular PN junction diodes that use two doped semiconductors (like silicon n-type and p-type), Schottky diodes use a metal-semiconductor junction. That metal-semiconductor junction is the whole star of the show, and it’s exactly what behaves differently when you apply reverse bias. Forward bias is when you push current through the diode easily—Schottkys are known for lower forward voltage drop, which is why people love them for things like switching power supplies, battery charging circuits, and solar panels. Reverse bias is the other side: when you apply voltage that makes the metal side negative and the semiconductor side positive, so ideally almost no current flows. That’s the “off” state, right?
Reverse bias stress is basically when you keep applying that reverse voltage for a long time, or cranked up higher than the diode’s rated reverse breakdown voltage, over and over. A lot of people new to diodes mix up reverse leakage current (the tiny little current that still flows when reverse biased, which is normal) and reverse bias stress (which causes damage over time). Let’s clarify that first: leakage is like a leaky faucet that still works, stress is like leaving the faucet open so long it rusts the pipe.
So what actually happens to the Schottky junction under reverse bias? Let’s get down to the physics, but make it simple. When you apply reverse bias, you’re pulling electrons away from the metal-semiconductor junction, right? That creates a depletion region—an area with very few charge carriers, sort of like an empty buffer zone between the metal and the semiconductor. For PN junction diodes, that depletion region is mostly in the lightly doped semiconductor side, but Schottky junctions are different because the semiconductor doping is typically higher. Wait, no—actually, the depletion region in Schottkys is thinner than in a comparable PN junction, that’s part of why their forward voltage is lower. But that thin depletion region is also their Achilles heel when reverse bias is involved.
Under continuous reverse bias, electric field starts building up in that depletion region. If you stay under the rated reverse voltage (Vr) listed on the diode’s datasheet, that field stays within safe limits—no problem, the diode will just sit there with that tiny leakage current, no issues even over years. But if you push it above Vr, or keep it at a high reverse voltage for extended periods, that electric field gets strong enough to do two main bad things, depending on the diode’s material and design.
First, there’s avalanche breakdown. That’s when the electric field is so strong it slams electrons loose from their atoms in the semiconductor, creating more electrons and holes, which then slam into other atoms, causing a cascade of current. For regular diodes, that’s basically what happens when they break down. But Schottkys have a lower avalanche breakdown voltage than many PN diodes because that thin depletion region. Wait, but there’s another thing specific to Schottkys: hot carrier injection, or sometimes called Schottky barrier lowering. That’s the tricky one that’s not as talked about as avalanche, but it’s way more common in real-world reverse bias stress situations.
Here’s how hot carrier injection works, in plain terms. The metal-semiconductor barrier is what keeps current from flowing reverse, right? But when you apply reverse bias, and the electric field in the depletion region is cranked up, some of the charge carriers (electrons, usually, since Schottkys use n-type semiconductors most of the time) get enough energy to jump over that barrier, even if they don’t have enough energy normally. Those are “hot carriers”—high-energy charge carriers that don’t behave like the sleepy, low-energy ones we see under forward bias.
Now, what do these hot carriers do? They bang into the crystal lattice of the semiconductor, knocking loose atoms or creating defects in the material over time. That’s called device degradation, and it’s gradual at first—hard to spot. At first, your reverse leakage current will start creeping up, not by much, maybe just a few microamps. That’s a warning sign, like your car’s check engine light being on for a tiny problem. If you keep pushing, keep applying reverse bias stress without fixing whatever’s causing it (maybe a bad design, or a diode that was rated too low for your circuit), those defects pile up. Eventually, the barrier gets messed up enough that leakage current spikes, and the diode might start leaking so much it can’t turn off anymore, or even short out entirely.
Wait, let’s make this real with an example, because examples stick. Last year, we had a customer come to us from a small automotive startup. They were using our 100V Schottky diodes in a battery management system (BMS) for electric motorcycles. Their circuit required the diodes to hold 95V reverse continuously, which was under our rated 100V Vr, or so they thought. But here’s the catch: automotive circuits have voltage transients—spikes that happen when the engine is turned on, or when the battery is connected wrong. They didn’t account for a 120V transient that lasted 10 milliseconds every time they started the bike. Over a month of testing, those transients were acting like repeated reverse bias stress pulses, and the diodes’ leakage current went from 1µA to 2mA, which was way too high for their BMS to work.
They were worried it was a bad batch of diodes, so they sent us samples, and we tested them in our lab. Turns out, it wasn’t the diodes’ fault—they were correctly rated for 100V, but the application had transient reverse bias stress that they didn’t calculate for. We recommended they step up to our 150V Schottkys, which have a higher breakdown voltage and thicker depletion region that handles those transients way better, and added a small TVS diode to clamp the spikes. That fixed their problem, and they’ve been a repeat customer ever since. That’s the kind of stuff we deal with every day, so we know reverse bias stress isn’t just a theory—it’s a real pain point that comes down to matching the diode to the application.
Now, let’s clear up some common myths about Schottky diodes and reverse bias stress. First myth: “All Schottkys fail immediately under reverse bias.” No—if you stay within the datasheet ratings, they’re super reliable. The 1mA reverse leakage we mentioned earlier? That’s normal for most Schottkys, and it doesn’t cause degradation over time. Second myth: “Reverse bias stress only happens when you exceed breakdown voltage.” Not always. Even if you stay under Vr, if you’re at a high reverse voltage for thousands of hours, you can get gradual hot carrier degradation. It’s not as fast as breakdown, but it’s a real issue for long-lifetime applications, like industrial power supplies that are supposed to run 24/7 for 10 years. Third myth: “Schottkys are worse than PN diodes for reverse bias.” It depends. If your application is switching frequencies above 100kHz, Schottkys are way better because of their lower reverse recovery time—PN diodes have that stored charge that causes extra loss when turning off. Reverse bias stress capability is just one part of the equation; you have to balance that with your other performance needs.
Another thing that affects reverse bias stress behavior: the type of Schottky diode. Ohmic contact Schottkys, barrier metal type—wait, no, more practical stuff: silicon vs. silicon carbide (SiC) Schottkys. SiC Schottkys are a newer option, and they handle reverse bias stress way better than regular silicon ones. Their depletion region is much wider, so avalanche breakdown happens at higher voltages, and hot carrier injection is way less likely. We have a lot of customers using SiC Schottkys for solar inverters, which need to hold reverse voltage for decades without failing—their reverse leakage is almost zero even at high reverse bias, so they don’t have that degradation issue. But SiC is more expensive, so it’s all about trade-offs. If you’re building a consumer gadget that only needs to last 2 years, a regular silicon Schottky is fine. If you’re building a wind turbine component that needs to last 25 years, SiC is probably worth the extra cost for that reverse stress reliability.
Wait, also, what about temperature? Temperature is a huge factor in reverse bias stress. The hotter the diode gets, the more severe reverse bias stress is. High temperatures make charge carriers more mobile, so hot carriers have more energy to cause defects. We did a test last quarter where we put our 60V silicon Schottkys under 55V reverse bias at 25°C (room temp) for 1000 hours—leakage stayed at 0.8µA, no change. Then we did the same test at 125°C, which is the max operating temp for most of our standard Schottkys. After 500 hours, leakage had jumped to 12µA, and after 1000 hours, it was 45µA. That’s a massive difference. So if your circuit runs hot (like a power supply in a small enclosure with no airflow), you need to derate your diode’s reverse voltage, not just use the rated Vr at room temp. That’s a mistake a lot of engineers make—they look at the datasheet Vr at 25°C and don’t account for derating at higher temps.
What can you do to avoid reverse bias stress issues, if you’re designing a circuit? We get asked this all the time, so here’s our go-to list of practical tips, not just theory. First, calculate all the reverse voltages your diode will ever see, including transients. Don’t just use the nominal reverse voltage—add a safety margin. A good rule of thumb is to pick a diode with a rated reverse voltage 20-30% higher than the maximum reverse voltage in your circuit, and more if there are big transients. Second, pay attention to operating temperature. If your diode will run at 100°C, derate the reverse voltage by at least 15% from the room temp rating. Third, if your application needs long lifetime (industrial, aerospace, solar), consider SiC Schottkys instead of silicon—they handle reverse stress way better. Fourth, watch out for overvoltage events, like reverse polarity or load dumps in automotive circuits. Adding a simple Zener diode or TVS across the Schottky can clamp those spikes before they damage it.
And if you do end up with a diode that’s failing from reverse bias stress, don’t just blame the diode. Most of the time, it’s a mismatch between the part and the application, not a bad batch. We’ve had customers send us diodes that were failing, and when we test them, the problem is that they were using a 20V diode in a circuit that needed 30V reverse, no derating, running at 100°C. That’s not a part defect—that’s an application mistake. But if you come to us with your circuit specs, we can help you pick the right Schottky, whether it’s standard silicon, high-temperature rated, or SiC, to avoid those issues.
At the end of the day, reverse bias stress isn’t something to fear—it’s something to understand. Schottky diodes are awesome for so many applications because of their speed and low forward drop, but that metal-semiconductor junction does have its limits under reverse voltage. The key is matching the diode’s ratings to your actual circuit conditions, not just the datasheet numbers on a random part you found online. We’ve been helping engineers do that for years, so if you’re dealing with reverse bias stress issues in your designs, or just need to pick the right Schottky for your next project, feel free to reach out. We don’t do hard sells—we’ll tell you if a standard part works, or if you need something custom, no pressure.
Digital Transistors REFERENCES
- Sze, S. M., & Ng, K. K. (2006). Physics of Semiconductor Devices (3rd ed.). John Wiley & Sons.
- Bhatnagar, M., & Baliga, B. J. (1993). Silicon carbide Schottky barrier diodes. IEEE Transactions on Electron Devices, 40(2), 645-655.
- National Semiconductor Application Note. (1998). Understanding Schottky Diode Reverse Bias Behavior and Reliability.
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