Lower Part Of Conduction Band Research Articles

Investigation of photo-induced effect on electrical properties of Au/PPy/n-Si (MPS) type schottky barrier diodes

Au/PPy/n-Si (MPS) type Schottky barrier diodes (SBDs) were produced and their current–voltage (I–V) characteristics were measured in the positive and negative bias regions at 300 K. The basic electronic quantities such as reverse-saturation current (Io), ideality factor (n), zero-bias barrier height (ФB0), series (Rs) and shunt resistances (Rsh) were obtained by using I–V data in total darkness and illumination (100 W/m2). The values of these parameters were found as 7.79 × 10−9 A, 5.41, 0.75 eV, 1 kΩ and 130 MΩ in dark) and 4 × 10−9 A, 4.89, 0.77 eV, 0.9 kΩ and 1.02 MΩ under illumination), respectively. Also the energy density distribution behaviors of surface states (Nss) have been acquired by calculation of effective barrier height (Фe) and ideality factor n (V) depending on voltage in total darkness and illumination. The values of Nss show an exponentially increase from the mid-gap of Si to the lower part of conduction band (Ec) for two conditions. The possible current conduction mechanisms were determined by plotting of the double logarithmic I–V plots in the positive voltage zone and the value of current was found proportional to voltage (I∼Vm). The high values of n and Rs were ascribed to the certain density distribution of Nss localized at semiconductor/PPy interface, surface conditions, barrier inequality, the thickness of PPy interlayer and its roughness. The open-circuit voltage of the photodiode was found as 0.36 V under 100 W/m2 illumination level. This is evidence that the fabricated sample is very sensitive to illumination. Therefore, it can be put into practice in optoelectronic industries as a photodiode or solar cells.

Electronic structure and luminescence mechanisms in ZnMoO4 crystals

Calculations of the band structure, partial densities of states and optical spectra of permittivity, reflectivity and absorption of perfect ZnMoO4 crystal were performed using the full-potential linear-augmented-plane-wave method. It is shown that the calculated reflectivity spectra reproduce the main features of corresponding experimental spectra in the fundamental absorption region. The bandgap value of ZnMoO4 is estimated as Eg = 4.3 eV. Peculiarities of luminescence excitation spectra corrected for near-surface losses and losses on reflectivity are discussed, taking into account the results of the calculations. It is found that the energy structure of the lower part of conduction band is manifested in the excitation spectra of the intrinsic luminescence. The excitation spectra in the region 4.3–8.0 eV are formed by band-to-band electronic transitions mainly within the molybdate groups MoO42−, whereas electronic states of Zn2+ cations are not directly involved into the excitation processes. It is shown that the structure of the intrinsic luminescence excitation spectrum depends on the temperature and mechanisms of the structure modification are discussed.