I've been playing around with some ideas of electron-hole pairs in semiconductors lately, have realized that I'm confused about some basic conventions that maybe the physics forum community could help clear up. Let's imagine that we have a direct gap semiconductor initially at zero temperature. I shine exactly one photon on the system and it excites an electron-hole pair such that the final state of the system now contains an electron with energy E1 in state "k" in the conduction band, and a vacancy at energy -E2 in state "k" in the valence band (energies are relative to the chemical potential and we'll assume that the photon contributes a negligible amount of momentum to the problem). My question is: according to standard conventions, what is the crystal momentum of the hole that has been created in the valence band? If I were to draw an analogy to electron-positron creation in particle physics, it would seem that the momentum ought to be "-k", but in the textbooks I've read so far, people seem to prefer leaving the hole at positive "k" and negative energy. If the latter convention is the case, wouldn't that seem to rather mangle up the standard equations for conservation of energy and momentum?