The exciton is a hydrogen atom-like entity encountered in advanced semiconductor work.It consists of an electron bound to a +q charged particle (a hole) of approximately equal mass. Bohr atom results can be used in computing the allowed cnergy states of thc exciton providcd the reduced mass, m, = m+m.J(m+ + m_) '" mo/2, replaces the electron mass in the Bohr atom formulation. In addition, the distancc between the components of the exciton is always such that there are intervening semiconductor atoms. Thus Co in the Bohr formulation must also be replaced by Ksco, where Ks is the scmiconductor dielectric constant. Using Ks = 11.8, determine the ground state (n = 1) energy of an exciton in Si.