Hi guys I just wanted to make sure I was thinking about this the right way. So in indirect bandgap semiconductors absorption needs a phonon to assist the electron to the conduction band from the valence band because a photon has virtually no momentum and only contributes energy to the electron while a phonon can supply the momentum needed to sort of go horizontally (k axis) on the band structure diagram. Im just confused with what the phonon actually does with the electron. Does it collide with the electron to transfer its momentum? Also was wondering what effect does the actual placement of the minimum of the conduction band and maximum of the valence band have on the phonon needed to make the jump. Im assuming if less momentum is needed to make the jump (min on left max on right) the phonon needed would have to have a negative momentum relative to the maximum point to assist the electron? Thanks for the help!