Why silicon takes 0.7v and germanium 0.3v for biasing?

Why silicon takes 0.7v & Germanium 0.3v for biasing?...

Re: Bias-Voltage

It is the property of the material

Here are the forward drops at 25•C
Ge 0.27V
Si 0.71V
GaAs 1.03V

For more information see https://en.wikipedia.org/wiki/Transistor

Re: Bias-Voltage

kumar_eee said:

Why silicon takes 0.7v & Germanium 0.3v for biasing?...

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for a diode to conduct current ,applied force(volt) should dominate the barrier potential( potential of depletion region--it's own potential formed due to coupling of two elements p and n)for si, barrier potential is .7 and for Ge it is .3v...so for current flow across the respective elements,applied volt must cross .7 or .3....

Re: Bias-Voltage

electronics_kumar said:

kumar_eee said:

Why silicon takes 0.7v & Germanium 0.3v for biasing?...

Click to expand...

for a diode to conduct current ,applied force(volt) should dominate the barrier potential( potential of depletion region--it's own potential formed due to coupling of two elements p and n)for si, barrier potential is .7 and for Ge it is .3v...so for current flow across the respective elements,applied volt must cross .7 or .3....

Click to expand...

As kumar said, it all depend on the doping material used, therefore each material will have it own threshold voltage to comeover in order to be operated, in other word they have their own voltage barrier to come over before turn on the device.

Re: Bias-Voltage

barrier potential is develop due to the Depletion Region. as p region contain hole and n region contain electronic. when these two layers combined togther they defuse with each other and make a wall of ion and behave as a battery.
(0.7v for silicon and 0.3v for germ).
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html#c3
For general use, where the size of the forward voltage drop is less important, silicon diodes are better because they are less easily damaged by heat when soldering, they have a lower resistance when conducting, and they have very low leakage currents when a reverse voltage is applied.
basically barrier potential indicates the number of holes and electronics combined.
it depend on the inherent properties of the semiconductor as well as impurities.
RAZA

Bias-Voltage

Aren't Schotkey diodes constructed to have a forward voltage of only .3 volts? Is there an equivilant form of Schotkey germanium didoe to get bellow .3 volts?

Re: Bias-Voltage

I have never heard of a Schottky built with Germanium ... for more information on the Schottky diode take a look here.

https://en.wikipedia.org/wiki/Schottky_diode

A Schottky diode uses a metal-semiconductor junction as a Schottky barrier (instead of a semiconductor-semiconductor junction as in conventional diodes).

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Re: Bias-Voltage

back to semiconductor physics.
remember the pn junction when not biased ;electrons from donor atoms attraced to holes from acceptor atoms,leaving a region called the depleted region,which is empty from free carriers ( because electrons and holes engaged to make the electron-hole pairs).
in energy levels this region has a voltage called the barrier voltage,due to carrier pairs.in silicon its found that we need 0.7 volts (in forward bias) to break the barrier voltage and narrow the depleted region as possible for free carriers to pass it as diffusion current for holes and drift current for electrons.
in germanium it is only0.3.

Bias-Voltage

A Schottky diode doesn't have a PN junction.. It's a metal to semiconductor junction. Silicon Schottky's are supposed to have only a .3 volt drop. What I was asking is what about (if it's appliciable) a Germanium based schottky diode? Or does it not work on Germanium semi conductors?

Re: Bias-Voltage

Muhammad Raza said:

.
basically barrier potential indicates the number of holes and electronics combined.
RAZA

Click to expand...

justify ur answer with proper explanation....is there any expression to find barrier potential from the knowledge of no.of electrons and holoes that combined....

thxin anticipation

Re: Bias-Voltage

silicon has forbidden band gap of 1.21eV whereas it is 0.78eV for germenium. hence silicon takes heigher voltage for biasing.