LED glows in reverse polarity phenomenon - Page 1
Forum section: electronics / projects

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: March 04, 2024, 04:04:59 am
content: Hi, I'm not sure if this post fits here, so mods, feel free to move it or delete it if it doesn't.Today, out of sheer boredom, I decided to put an LED in its reverse polarity in my 5CT1N curve tracer. I wanted to destroy some LEDs just for the fun of it. But this particular LED survived the curve tracer which can reach 200v. This was mostly due to the LED loading down the output to a maximum of 48 volts.I also noticed an interesting phenomenon, where the LED glows in reverse polarity. The glow is similar to a small incandescent lamp being lit dimly, but the LED shows no signs of damage. The LED still works just fine after, and I do not see any kind of burnt resin. This piqued my interest as usually, an LED shouldn't glow in reverse polarity, but my test was under extreme conditions. The LED is green, but it glows a warm color in reverse.This LED is NOS. Likely 1980s or 90s.I searched around the internet but could not find anything resembling my test.Perhaps someone here on the forum could explain this?Here are some quantitative measurements I could take from this LED via the 5CT1N.Peak reverse current at -48v: 6.4mAForward voltage drop of 1.775v

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: March 04, 2024, 04:06:47 am
content: LED glowing in the correct polarity after being subjected to the -48v reverse.For the graph, 20v horizontal, 1mA vertical.

author: Andy Chee
author_rank: Super Contributor
timestamp: March 04, 2024, 04:55:41 am
content: Quote from: BlownUpCapacitor on March 04, 2024, 04:04:59 amIMSAI guy puts a few different colour LEDs onto a curve tracer, including reverse voltage.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: March 04, 2024, 07:26:55 am
content: The phenomenon is present in most semiconductor, and related to the "hot" carriers that are generated during the avalanche (sometimes called "hot carriers luminescence"). Essentially, electrons and holes are accelerated by the high electric field, and release their energy as photons, by effectively glowing. This even happens in silicon, where avalanche diodes can release some photons during the avalanche. Silicon avalanche LEDs were even proposed, even though I am not sure anybody uses themhttps://www.intechopen.com/chapters/47465The spectrum of the light emitted is rather broad, not like a conventional LED, and the efficiency of the process is abysmal, but it's the only way to get useful light out of the indirect bandgap of silicon.

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2024, 09:00:17 am
content: Now try that with modern, pure green, blue or violet LED and it'll be destroyed.Older LEDs tend not to be damaged by reverse breakdown an non-destructively avalanche. Newer InGaN are much more sensitive to reverse voltages.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 04, 2024, 09:11:37 am
content: You may like this topic, has many reverse polarized glowing junctions:https://www.eevblog.com/forum/projects/transistors-die-pictures/