Diode and very small amplitude high frequencies signals

I need to clarify this. My comments apply only to junction diodes, which virtually all silicon diodes are. Schottky diodes don't exhibit this charge storage effect. That's one reason they're often used in high frequency switching supplies. Their leakage current is, however, much greater than silicon diodes.

Roy Lewallen, W7EL

Roy Lewallen wrote:

I'm not sure what you mean by an "offset" -- all diodes cross through the origin of the I-V curve, when excited by DC, anyway -- unless they contain a battery. In the reverse direction, the current pretty much levels off beyond a small reverse voltage. The current of this level part is the saturation current.

Again, don't think that good DC characteristics make for a good RF detector. A number of other factors, which have been discussed here, are very important. As I recall, only transistors designed as saturated switches (2N918 comes to mind, but it's been a long time, so don't quote me) are gold doped. Ones which aren't, and I'm quite sure the 2N3904 is in that category, will have long reverse recovery times so will make poor RF rectifiers. Circuits became too fast for saturated switches long, long ago, so I'd be surprised if gold doping is done any more except for replacement transistors in very old equipment.

You can learn a lot with a very simple setup consisting of nothing more than a variable amplitude signal generator, a diode, load resistor and capacitor, and a meter or scope. SPICE should also show these effects provided you use good models.

Roy Lewallen, W7EL

Yes.

CMOS has no storage.

No. Doping "sex" (of gold) is wrong for the N-type base, which is where you're trying to induce recombination.

...Jim Thompson

Sounds good to me, and it'll glow in the dark ;-)

...Jim Thompson

Don't people still use 2N2369As, or at least the plastic version? If not, what do they use instead?

(Does gold doping work for PNP transistors? I don't see why it wouldn't, but I've never seen a specific reference to a gold-doped PNP.)

I read in sci.electronics.design that Jim Thompson wrote (in ) about 'gold doping (was Re: Diode and very small amplitude high frequencies signals)', on Mon, 7 Feb 2005:

What to use, then? Ion-implanted krypton?

quote

is

wouldn't,

Without going into the details of Quantum chemistry and electronic configurations (which is certainly more challenging and exciting) you can easily see it from a simplified perspective of the energy bond model of semiconductors. For a npn transistor doped with Gold the equilibrium density (ed) for impurity electrons in Silicon doped with gold is given by the well known Fermi-Dirac statistics equation. ed = B*Nd*exp(-Edonors/kT) E donors is the energy required for Golds electron to freely dwell in the Silicon lattice ... a value much smaller then the E gap energy value for Si to create an electron hole pair. Smaller values of Edonor imply larger values free donor electrons.

If a pnp transistor was to be formed from Si doped with Gold the equilibrium density (ph) for impurity holes in Silicon doped with gold is ph = A*Na*exp(-Eacceptor/kT) Eacceptor is the energy required for a electron to be stripped from the Silicon atom by the Gold atom.

As Eacceptor is greater then Edonor only a npn transistor can be formed from Si doped with Gold.

Its even more exciting to look at the Physics of Gold plated transistors. Very intriguing .. just like the MOSFET transistor!