Quantum Confinement Effects for Semiconductor Clusters in the Molecular Regime

Based on the observed absorption spectral band shifts, the growth process of the semiconductor clusters was divided into two phenomenological regimes: The "molecular regime" that is associated with the band blue shift as the size of cluster increases and the "crystallite regime" that is associated with the band red shift as the size of cluster increases. We show that in the molecular regime, the band blue shift associated with cluster growth can be understood by a model that assume electrons are confined to a spherical potential well and the clusters are made of some basic units. A formula is given for the lowest excited electronic state energy. This expression contains an electron-hole-pair (EHP) delocalization constant as an adjustable parameter which, however, can be anchored to a definite value through the known transition energy at the spectra turn-around point. The stability of clusters is characterized by a function that can be calculated by the eigenvalues of the Hamiltonian of the model.