How to tell germanium from schottky diodes - Page 1
Forum section: electronics / beginners

author: vpittman
author_rank: Newbie
timestamp: February 16, 2021, 06:19:30 pm
content: I've heard that a lot of so called germanium diodes are actually schottky's. Is there and easy way to tell them apart ? The Vf of each of these is around 0.2 V so that's not a good indicator. Is there anything else that could be used to tell them apart ?There is a youtube video () and at 2:13 he compares a schottky to a silicon diode using an oscilloscope. Latter he increases the frequency from 60 Hz to 300 kHz and shows the the silicon diode has a reverse current leakage while the schottky does not (@ 3:20). Could this procedure be used with germanium as well ?Thanks !!Victor

author: Terry Bites
author_rank: Super Contributor
timestamp: February 16, 2021, 07:51:26 pm
content: Part number?

author: vpittman
author_rank: Newbie
timestamp: February 16, 2021, 07:57:47 pm
content: D9e

author: Kleinstein
author_rank: Super Contributor
timestamp: February 16, 2021, 08:00:35 pm
content: One may see a difference in the temperature dependence of the forward voltage or leakage current in reverse. Germanium has a significant lower bandgap energy - even with a shottky diode it is generally still silicon. I would expect more temperature dependence for the silicone based diode, not just normal PN diodes, but also Schottky diodes.

author: iMo
author_rank: Super Contributor
timestamp: February 16, 2021, 08:25:36 pm
content: Germanium diodes are always packaged in glass (or metal or ceramic).. I have never ever seen a germanium diode in plasticThe TC of Ge diodes (and transistors) is higher than the TC of the Si stuff. Also the forward drop with small signal Ge is usually a bit lower than with small signal schottky..

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 08:50:22 pm
content: Quote from: vpittman on February 16, 2021, 07:57:47 pmVery unusual partnumber for an American or Europian diode. But it is suspiciously very similar toold Soviet Д9Е(Д9 series) - small signal germanium diode (widely used in old AM radios etc.).If it is so then there is no need to make an experiment, and it will be hard to find a difference with a Shottky because those diodes are very fast too.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 09:00:01 pm
content: Quote from: Kleinstein on February 16, 2021, 08:00:35 pmYes, but there is not a significant or noticeable difference between germanium and Shottky types - both have large reverse DC current. And both types have similar (and large, I mean very significant) reverse current temperature dependence.

author: iMo
author_rank: Super Contributor
timestamp: February 16, 2021, 09:01:44 pm
content: The D9E has got typically Ir<250uA at Ur=10V. That is much higher Ir than with a schottky at ambient temp.Small signal schottky is typically 100nA-1uA Ir.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 09:08:13 pm
content: Quote from: imo on February 16, 2021, 08:25:36 pm+1, by the way: does it looks like as in an attachment?

author: iMo
author_rank: Super Contributor
timestamp: February 16, 2021, 09:10:32 pm
content: Small signal schottky are also packaged in glass - here helps following: Ge diodes are always bulkier

author: vpittman
author_rank: Newbie
timestamp: February 16, 2021, 09:52:25 pm
content: Very similar, but mine have a red and blue stripe

author: David Hess
author_rank: Super Contributor
timestamp: February 16, 2021, 09:53:34 pm
content: I have never seen a germanium diode in a plastic package so that helps a little. Small signal germanium diodes like the 1N34A and 1N270 also use the older DO-7 glass package which is larger and easy to distinguish from the smaller glass DO-35 package used by schottky diodes like the 1N5711, 1N6263, SD series, and BAT series and silicon switching diodes like the ubiquitous 1N4148.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 09:57:11 pm
content: Red and blue mean 'E', so it is D9E (again). It can be only blue or red+blue.D9E (Д9Е) is an analog to 1N34, but with a lower rated forward current (20 mA, +-). So possibly the case type is the same.

author: Circlotron
author_rank: Super Contributor
timestamp: February 16, 2021, 10:06:26 pm
content: Has there ever been a commercially available Schottky diode made from germanium?

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 10:09:59 pm
content: Here is a pic:

author: Kleinstein
author_rank: Super Contributor
timestamp: February 16, 2021, 10:11:02 pm
content: There are quite a few old parts, though I don't see much need for a Schottky diode made from germanium. The Germanium diode are usually fast and low voltage just like the modern silicon schottky diodes. So the problem is not to guess it a germanium diode is a actually schottky type, but to see if a diode is Si-Schottky or old style germanium.If they have the same - why care ?There were also a few JFETs based on Germanium, but I have never seen one in real life.

author: Circlotron
author_rank: Super Contributor
timestamp: February 16, 2021, 10:15:28 pm
content: I was meaning if there was a Schottky made from germanium would it have an even lower forward voltage drop than either silicon Schottky or normal germanium?

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 10:17:15 pm
content: Quote from: Circlotron on February 16, 2021, 10:06:26 pmThere were galena Shottky diodes, but I can't find any info about germanium ones existing:

author: vpittman
author_rank: Newbie
timestamp: February 16, 2021, 10:22:45 pm
content: The DO-7 package measures correctly, and if it's also as fast switching as a schottky then my idea of testing with high frequency won't work. I'll see if I can measure the leakage current in reverse.Why care? It's covid, I'm new and I'm learning all this stuff... I find it very interesting and it gives me something to do.And in this posthttps://www.eevblog.com/forum/beginners/is-it-really-germanium/msg2888454/#msg2888454there appears to be some difference, not really sure how much affect this will have

author: vpittman
author_rank: Newbie
timestamp: February 16, 2021, 10:26:22 pm
content: Quote from: Vovk_Z on February 16, 2021, 08:50:22 pmWhat do you look at in the datasheet to tell that these are 'fast' ?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 16, 2021, 10:35:01 pm
content: For the speed of a diode there are 2 parameters to look at: the main part is the reverse recovery time. The other parameter is the diode capacitance relative to the current rating.With a scope and function generator (square wave with reasonable fast edges , like from a 74HC gate) one can test the diode recovery quite easy. Look at the diode voltage and apply something like a +-2 V square wave with a series resistor of some 1 K ... 50 Ohms depending on the diode size.The curve of "junction" capacitance versus reverse voltage (especially the range of low votlages) could also tell apart some diodes. Chances are Germanium is different here too, as the build in voltage is naturally relatively small.

author: vpittman
author_rank: Newbie
timestamp: February 16, 2021, 10:56:46 pm
content: Thanks everyone for all the insight !!!

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 16, 2021, 11:00:25 pm
content: Quote from: vpittman on February 16, 2021, 10:26:22 pmFor soviet diodes, it was a parameter called "Max working frequency" (it was hard to understand what it really means), and for Д9Е it is 100kHz. As I know it works up to tens of megahertz (so thats why I say it is hard to understand some Soviet characteristics).

author: David Hess
author_rank: Super Contributor
timestamp: February 16, 2021, 11:03:27 pm
content: The 1N270s that I have used in power detectors were usable to 100s of MHz.Quote from: Circlotron on February 16, 2021, 10:06:26 pmThey were advertised at one point for high efficiency power supplies but obviously were not commercially successful.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2021, 12:09:21 am
content: So I'm following along hoping for a definitive answer, but I'm not sure of one yet.I also have some diodes I have questions about. They look like a DO-7 case, definitely larger than my 1N4148s. They have a Vfof 0.16V @ 100uA and 0.22V @ 1mA, IRat 10V is 1.1uA and really doesn't change much if I warm it up with my fingers. They appear to be marked 'DJ 025 T' and they were sold by a surplus dealer as 1N34A germanium. What do I have?

author: MikeK
author_rank: Super Contributor
timestamp: February 17, 2021, 04:04:34 am
content: How to discern Germanium-Diodes from Schottky-Diodes:

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2021, 05:05:09 am
content: I saw that video and I noted that the narrator claims that the reverse leakage characteristics of germanium diodes are innate and universal to the type. IOW, there are no low-leakage germanium diodes.But this manufacturer claims to manufacture low-leakage germanium diodes.https://www.americanmicrosemi.com/tutorial/germanium-diodes/Their version of 1N34A has a max IRof 30uA @ 10V, and I assume this would be at the maximum temperature of 90C.I don't have a PSU on the bench at the moment that can give me 40mV like in the video, but I just tried it at ~0.1V, 0.5V and 10V and I got leakage currents of 0.3uA, 0.35uA and 1.2uA respectively. It seems to not go up that much with voltage. Then I tried warming it up with a heat gun set to 100C from a small distance, at 10V I was able to get the leakage current over 30uA.So, I still don't know. And I can't find the marking DJ 025 T (three lines) anywhere.