Photovoltaic and interface state density properties of the Au/n-GaAs Schottky barrier solar cell

The electrical and photovoltaic properties of the Au/n-GaAs Schottky barrier diode have been investigated. From the current-voltage characteristics, the electrical parameters such as, ideality factor and barrier height of the Au/n-GaAs diode were obtained to be 1.95 and 0.86 eV, respectively. The interface state distribution profile of the diode as a function of the bias voltage was extracted from the capacitance-voltage measurements. The interface state density D_it of the diode was found to vary from 3.0 × 10¹¹ eV⁻¹ cm⁻² at 0 V to 4.26 × 10¹⁰ eV⁻¹cm⁻² at 0.5 V. The diode shows a non-ideal current-voltage behavior with the ideality factor higher than unity due to the interfacial insulator layer and interface states. The diode under light illumination exhibits a good photovoltaic behavior. This behavior was explained in terms of minority carrier injection phenomenon. The photovoltaic parameters, such as open circuit voltage and short circuit current density were obtained to be 362 mV and J_sc = 28.3 μA/cm² under AM1, respectively.     

Modification of metal/semiconductor junctions by self-assembled monolayer organic films

Two new metal/molecule/semiconductor contacts, Au/n-Si/TDA/Au and Au/p-Si/ODM/Au, were fabricated to understand effect of organic compounds, tridecylamine and octadecylmercaptan self-assembled monolayer (SAM) films, on electrical charge transport properties of the metal/semiconductor junctions. The morphology of the organic monolayers deposited on Si substrates was investigated by atomic force microscopy. The molecular coverage of ODM deposited on p-Si is poorer than that of TDA on n-Si substrate. The ideality factors of the p-Si/ODM and n-Si/TDA diodes were found to be 1.66 and 1.48, respectively. The electrical results show that the tridecylamine monolayer passivated junction has a lower ideality factor. The ideality factor indicates clear dependence on two different type functional groups R-SH (Thiol) and R-NH₂ (Amin) groups and it increases with different functional groups of organic molecule. The barrier height φ_b value of the n-Si/TDA diode is smaller than that of p-Si/ODM diode, as a result of chain length of the SAM organic molecules. The interface state density D_it values of the diodes were determined using conductance technique. The n-Si/TDA diode has the smaller interface state density according to p-Si/ODM diode.We have evaluated that the organic molecules control the electronic parameters of metal/semiconductor diodes and thus, organic modification helps to get one step closer towards to new organic assisted silicon based microelectronic devices.     

Temperature dependence of the optical band gap and refractive index of poly(ethylene terepthalate) oligomer–DDQ complex thin film

The temperature dependence of the optical band gap and refractive index dispersion of thin film of poly(ethylene terepthalate) oligomer–DDQ charge transfer complex has been investigated. The absorption edge shifts to the lower energy as consequence of the thermal annealing on film and the fundamental absorption edge corresponds to a direct energy gap. The temperature coefficient of the optical band gap for the film was found as dE_g/dT = − 3.15 × 10⁻³ eV/K. The temperature dependence of the refractive index has also been investigated and it is observed that the refractive index changes by annealing temperatures.     

Genetic programming approach to predict a model acidolysis system

This paper models acidolysis of triolein and palmitic acid under the catalysis of immobilized sn-1,3 specific lipase. A gene-expression programming (GEP), which is an extension to genetic programming (GP)-based model was developed for the prediction of the concentration of major reaction products of this reaction (1-palmitoyl-2,3-oleoyl-glycerol (POO), 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and triolein (OOO). Substrate ratio (SR), reaction temperature (T) and reaction time (t) were used as input parameters. The predicted models were able to predict the progress of the reactions with a mean standard error (MSE) of less than 1.0 and R of 0.978. Explicit formulation of proposed GEP models was also presented. Considerable good performance was achieved in modelling acidolysis reaction by using GEP. The predictions of proposed GEP models were compared to those of neural network (NN) modelling, and strictly good agreement was observed between the two predictions. Statistics and scatter plots indicate that the new GEP formulations can be an alternative to experimental models.     

Temperature dependence of electronic parameters of organic Schottky diode based on fluorescein sodium salt

The electrical properties of an organic Schottky diode based on fluorescein sodium salt were investigated by current density–voltage and capacitance–voltage measurements. The crystal structure of fluorescein sodium salt, FSS in powder form was analyzed by X-ray diffraction method. X-ray diffraction results showed that the fluorescein sodium salt has a polycrystalline structure with a monoclinic system. The current density–voltage and capacitance–voltage characteristics of Al/FSS Schottky diode were investigated in the temperature range of 300–400 K. The diode exhibits a rectifying behavior, indicating the formation of the Schottky type junction at the interface of Al/FSS. The predominant charge transport mechanism of the Al/FSS Schottky diode was discussed and the proposed current injection processes was presented. The temperature dependence of the calculated acceptor concentration, the built-in potential and the width of the depletion region of Al/FSS Schottky barrier was also determined.     

Nanopowder synthesis of aluminum doped cadmium oxide via sol-gel calcination processing

The structural, optical and electrical properties of undoped and Al-doped CdO powder nanostructures prepared by sol-gel calcinations method have been investigated. X-ray diffraction (XRD) results revealed that pure and Al-doped CdO have the polycrystalline with face centered cubic (FCC) structure. The crystallite size for undoped and 5, 10, 15, 20% of Al-doped CdO samples were found to be 17.2, 15.9, 16.1, 16.3 and 16.8 nm, respectively. The optical band gap of the samples were determined from the diffused reflectance spectra and E_g values for undoped and 5, 10, 15, 20% of Al-doped CdO samples were found to be 1.89, 2.07, 2.03, 2.07 and 2.12 eV, respectively. The electrical conductivities of pure and Al-doped CdO were measured in the temperature range (290-420 K) and their temperature dependence was analyzed according to Arrhenius relation. The electrical conductivity results indicate that the electrical conductivity mechanism is controlled by thermally activated processes. The results showed that sol-gel calcinations technique can be effectively used to produce undoped and doped nanopowders.     

Controlling of crystal size and optical band gap of CdO nanopowder semiconductors by low and high Fe contents

The CdO:Fe nanopowder semiconductors were synthesized by the sol?Cgel calcination for the first time. The structural properties of Fe doped CdO samples were analyzed by AFM and XRD measurements. XRD patterns of the pure and Fe-doped CdO samples reveal that the pure and Fe doped CdO nanopowders are polycrystalline of cubic CdO structure. The crystallite size of undoped and Fe-doped CdO samples is changed unsystematically with a regular increase of Fe content. The optical band gaps of Fe doped CdO samples were determined for the first time by diffused reflectance measurements. The optical band gap of the samples is increased with the increase of Fe dopant inside the host matrix (CdO) up to 15?% followed by a decrease in its value. It is evaluated that Fe doped CdO nanopowder semiconductors can be producted by sol?Cgel calcination for advanced technological applications     

Electrical characteristics and photosensing properties of Al/symmetrical CuPc/p-Si photodiodes

Journal of Materials Science: Materials in Electronics - In this study, the symmetrical copper-phthalocyanine (CuPc) was coated on p-Si wafer by spin-coating method. The photoresponse and...