4H-SiC is doped with 2 x 1017 cm-3 nitrogen donor atoms (Ec - Ed = 90meV). Use Nc = 4 x 1020 cm-3. a. Calculate the electron density at 300 K. b. Calculate the hole density at 300K after adding 2 x 1018 cm-3 aluminum acceptor atoms ( Ea - Ec = 220 meV). Use Nv = 1.6 x 1020 cm-3.