Sketch the energy band structure of silicon with a band gap of 1.1 eV. What elements would you add to silicon to make it p-type? Sketch the resulting energy level structure for acceptor levels that are located 0.01 eV above the top of the valence band. What fraction of the acceptor levels would be occupied at room temperature? Assume that the probability of excitation is proportional to exp(–E/kT). If the impurity concentration is 10−4 at.%, what is the carrier density due to the impurities? What would be the intrinsic carrier concentration at room temperature, in the absence of impurities? At what temperature is the intrinsic density equal to that caused by the impurities?