State density in a semiconductor refers to the number of available energy states per unit volume in the energy band structure of the material.
As temperature increases, the state density in a semiconductor also increases due to the increase in thermal energy, which allows more electrons to occupy higher energy states.
The conduction band state density refers to the number of available energy states for electrons to move freely, while the valence band state density refers to the number of available energy states for electrons to be bound to atoms.
Doping, which involves intentionally adding impurities to a semiconductor, can significantly alter the state density by introducing additional energy levels in the band structure and shifting the balance between conduction and valence band state densities.
The state density and carrier concentration in a semiconductor are directly proportional, meaning that an increase in state density will result in an increase in the number of carriers (electrons or holes) in the material.