if one do a resistance test for forward and reverse biasing on a Silicon and a Germanium diode the result is that the ratio of reverse/forward is much bigger for Silicon than for Germanium. The question is Why?
I have done some reading on the two diode and found that germanium diode has a bigger leakage current than Silicon diodes. My theory for this is that Germanium valence electrons are at a higher level of energy.
Can someone please assist in this matter?

 

Actually you have it backwards. It takes less energy to bridge the gap in germanium, which is why the PN voltage drop is much less. Leakage doesn't necessarily have anything to do with energy gaps IMO.

 

Thank you very much for taking the time to answer me. It has pointed me in the right direction. This is to answer why silicon diodes is better than germanium diodes. Im still working through the theory and i will post as soon as i have a answer in order to share.

 

Because Germanium valence electrons are at higher energy levels than silicon, less energy is required for Germanium electrons to escape the atom. This makes Germanium less stable than Silicon. Germanium diodes work well at high frequencies and low current and voltage but not at high current and voltage. This is where silicon makes a better diode with a bigger operational range.

 

While germanium and silicon are the preferred and best materials used for BJTs, they aren't the only materials. There are many materials in the semiconductor region, such as carbon.

I suspect the real reason these two materials are used is our ability to make really pure crystalline ingots from semiconductor furnaces. Doping of impurities that make the P and N materials on a wafer is typically less that 1 part per million. This is planned impurities, I suspect that much more than 1per 1 billion unplanned impurity is enough to ruin a wafer.