Excitonic transitions and exchange splitting in Si quantum dots

In a quantum dot made of an indirect gap material such as Si, the electron- hole Coulomb interaction alone can give rise to "dark" excitons even in the absence of exchange interaction. We present the predicted excitonic spectr a for hydrogen-passivated Si dots and find very good agreement with the rec ent experiment of Wolkin, Jorne, Fauchet, Allan, and Delerue [Phys. Rev. Le tt. 82, 197 (1999)]. The calculated splitting between dark and bright excit ons, arising from Coulomb and exchange interactions, agrees very well with the optical data of Calcott, Nash, Canham, Kane, and Brumhead [J. Phys Cond ens. Matter 5, L91 (1993)]. (C) 1999 American Institute of Physics. [S0003- 6951(99)04845-7].