Hi and thanks for reading, I dont really understand the valleys in the conduction band, in the E vs. k diagram, there is the L-valley, r-valley and X-valley. Each has a different momentum... and are at different energy levels. I understand that at any temperature above absolute zero, a small fraction of electrons will acquire enough energy to jump to the conduction band (overcome the energy gap Eg). The GaAs bandstructure here: http://www.ioffe.ru/SVA/NSM/Semicond/GaAs/bandstr.html I assume most electrons which acquire enough energy will jump to the lowest valley in the conduction band (r-valley for GaAs). Ive been trying to determine what is the 'effective' temperature necessary to move an electron from the r-valley to the L-valley, the difference is 0.29 eV in GaAs. Is the additional thermal energy comming from E = kT ? ... therefore T = 0.29eV*q/(k) ??? this is a large temperature .... this seems too large ~3,600 °K. How do the electons move between valleys ? And how does one find the required energy for this to take place ? Thanks for any help you can provide.