npn/pnp TR differences

[bogito]

anyone who knows other differences between npn and pnp transistors excluding the polarity?

The resistance between emitter and collector is to be considered as a difference?

 

[Roff]

The fundamental difference between NPNs and PNPs is the majority carrier. In NPNs, electrons are the majority carrier, i.e. electrons are what flows from emitter to collector, constituting current flow. In PNPs, holes, which are spaces in the semiconductor lattice that are available for electrons to occupy, are the majority carrier. For some reason, which I may have known at one time, electron mobility is about twice that of hole mobility. I'm not sure of all the implications of this, but the bottom line is that NPNs are generally of higher "quality" than PNPs. This is especially true at high frequencies. I suspect you will never find circuits which operate in the tens of gigahertz range made with PNPs.
If there are any semiconductor physicists in the audience, help me out. I'm in over my head here!

 

[crust]

Hello Ron, I'm a EE and not in the area of device physics, but I believe I remember the reasoning as follows:

The reason the mobility of the electron is higher than that of the hole (in most cases ... i believe there are materials in which this is not the case) is because the effective mass of the hole is greater than the effective mass of an electron.

Because electrons in a lattice structure are not in "free space", we can't use the regular mass in our regular "particle in solid analysis". Rather, the effective mass is used to account for the influences from the lattice structure. The carriers can then be treated as "almost free".

 

[bogito]

a-ha...
i see.

thnx a lot guys!

 

[rookie]

npn can be switced with only a +signal, pnp -signal..m i true ere?

 

[Roff]

npn can be switced with only a +signal, pnp -signal..m i true ere?

True. The base-emitter voltage of an NPN will be about +0.7 volts when the transistor is on. For a PNP, the base-emitter voltage will be approximately -0.7v when it is on. In Bogito's original post, he specifically said "excluding the polarity", so I didn't mention it.

 

[rookie]

thanks to u Ron,but equipt/people use more npn's compare to pnp's.

 

[Roff]

thanks to u Ron,but equipt/people use more npn's compare to pnp's.

Well, I did point out that NPNs are generally higher "quality" than PNPs, so it follows that NPNs would be prevalent. What's your point?

 

[rookie]

thanks to u Ron,but equipt/people use more npn's compare to pnp's.

Well, I did point out that NPNs are generally higher "quality" than PNPs, so it follows that NPNs would be prevalent. What's your point?

Oooops sorry Ron,so it is the quality