I only just saw your visitor message from over a month ago!
To clarify, no it is not a requirement for semiconductors to be group IV, there are numerous compound semiconductors which do not have group IV elements in them at all, one of the most common being Gallium Arsenide (GaAs). However, although I don't agree with it, for the purposes of the HSC, we really only look at 'element' semi-conductors, all of which are Group IV -- the semiconductors we always talk about are the ones with 4 electrons in their valence shell. Your teacher is probably the same, although there are many more answers, he/she wants the students to use the ones which would earn them marks in the HSC.
Unfortunately with the HSC, sometimes knowing too much is a disadvantage :\