Transmission spectrum

[Ji]

Hi,
I have a question regarding the transmission spectrum. Ideally, the transmission spectrum should be always less than 1. How come I got it larger than 1.  My another question is what is transmission spectrum actually explaining? For instance, Is it talking about the transmission coefficient which describes the probability that  particles are going from conduction band to valence band?
I really need the answer in a hurry.
Thanks
Ji

[Petr Khomyakov]

I have a question regarding the transmission spectrum. Ideally, the transmission spectrum should be always less than 1. How come I got it larger than 1.

This is a wrong statement. The transmission spectrum corresponds to the total transmission defined as a sum over all the transmission modes for a given electron energy. Transmission coefficient for a single electron propagating mode can not be larger than 1 indeed, but the sum over the modes is only bounded by the number of propagating modes in the system. The latter depends on the band structure of the electrodes comprising the device. 

My another question is what is transmission spectrum actually explaining? For instance, Is it talking about the transmission coefficient which describes the probability that  particles are going from conduction band to valence band?
I really need the answer in a hurry.

The transmission spectrum allows you to compute the electron conductance and current, and this is the essential quantity in electron transport calculations. I would suggest you to read some textbooks (e.g., a book by S. Datta, https://www.cambridge.org/core/books/electronic-transport-in-mesoscopic-systems/1E55DEF5978AA7B843FF70337C220D8B) and original papers on the electron transport.