Question

Carbon is not a semiconductor in spite of being 14th group why

Answer 1

there are so many exception in chemistry

Answer 2

Si, and Ge, although part of same group as Carbon, are atoms of higher order, I. E, they belong to the 2nd and 3rd period respectively. So, their valence orbital electrons are less tightly held by the nucleus due to which lesser ionization energy is required to free an electron from the nucleus of Si and Ge. However for C, the ionization energy required to make an electron mobile is higher, and do at room temperature, there is not any notable conduction due to lesser electrons freed from the nucleus.