A new theory is developed for nonideal J-V characteristics of Schottky barriers with an interfacial layer. This theory is based on the model that nonideal characteristics are due to changes of population in the interface states under applied bias and accompanying changes of the barrier height. The population in the interface states is expressed by the Fermi level, which can be determined by analyzing experimental results. The J-V characteristics are obtained from the flow of carriers into and out of the interface. Tunneling through the interfacial layer constitutes the bottleneck for the carrier flow. Under forward bias, the carrier concentration ns at the interface is proved to be in thermal equilibrium with the bulk. Under reverse bias, ns is in local thermal equilibrium with the interface states. This theory is applied to an undoped a-Si:H Schottky barrier without introducing any ambiguous quantities. The experimental ideality factor, its dependence on temperature and voltage, and current density are quantitatively explained. By analyzing experimental results, the following behaviors are disclosed. The Fermi level of the interface states is significantly lower than the bulk Fermi level at low forward bias, but it approaches the bulk Fermi level with increasing forward-bias voltage. As for the reverse characteristics, the decrease of the barrier height is proportional to √V in the present sample for applied voltage V. For electrons in the interface states, the probability of tunnel transition to the metal is small compared with that of communication with the conduction band.

Change in the electronic state due to size confinement was studied for the CdS cluster embedded in GeO2 glass by photoacoustic, optical absorption and photoluminescence spectroscopies. The cluster size increases with increasing annealing temperature and time. The activation energy of ion diffusion during cluster growth is 0.45 eV. When the cluster size becomes less than about twice the exciton size, the energy bands become discrete. The energies of 1st and 2nd excited states increase with decreasing cluster size. The size dependence of the ist excited state determined experimentally coincides with the calculation. The energy of the surface state also shifts in parallel with the shift of the 1st excited state. When the cluster size decreases, the intensity of the edge emission decreases faster than that of the surface emission.

No abstract