[time-nuts] TAPR TICC boxed (input protection)

[David]

On Fri, 7 Apr 2017 04:09:38 -0400, you wrote:

>David wrote:
>
>>> what doping is used for PNP RF transistors and saturated switches
>>> if it is not gold?  Does it also increase leakage?
>
>I replied:
>
>> Gold doping doesn't affect the speed of BJTs in the active region very
>> much -- its purpose is to reduce minority carrier lifetime and, thereby,
>> to reduce storage time when a transistor recovers from saturation.  I'm
>> not sure how manufacturers deal with this in the case of PNPs.
>
>After I posted, I recalled learning in a long-ago device physics course 
>that both Gold and Platinum doping were used to reduce minority carrier 
>lifetime in PNP saturated switches.  According to Motorola, the 
>MPS3639/3640, 2N4209, and 2N5771 were gold-doped PNP saturated switches 
>(all are now obsolete, although SMD versions of the 3640 and 5771 appear 
>to still be available).
>
>And yes, doping PNPs with either Gold or Platinum does increase reverse 
>leakage current (Platinum less so than Gold).
>
>Best regards,
>
>Charles

So gold doping does work with PNP devices.  Previously when I brought
it up, I was told gold doping only applied to NPN devices leading to
my confusion.