The determination of interface state energy distribution of the H-terminated Zn/p-type Si Schottky diodes with high series resistance by the admittance spectroscopy

Analysis of Zn/p-Si Schottky diodes (SDs) with high resistivity has been given by admittance spectroscopy. The importance of the series resistance in the determination of energy distribution of interface states and especially their relaxation time in the SDs with high resistivity has been considered. The effect of the series resistance on capacitance-conductance/frequency characteristics has been given by comparing experimental data with theoretical data. The interface state density N_ss from the admittance spectroscopy ranges from 1.0×10¹² cm⁻² eV⁻¹ in 0.720-E_v eV to 2.03×10¹² cm⁻² eV⁻¹ in 0.420-E_v eV. Furthermore, the relaxation time ranges from 4.20×10⁻⁵ s in (0.420-E_v) eV to 3.20×10⁻⁴ s in (0.720-E_v) eV. It has been seen that the interface state density has a very small distribution range (1.0-2.03×10¹² cm⁻² eV⁻¹) that is ascribed to the predominant termination with hydrogen of the silicon surface after HF treatment.     

Electrical characteristics of Au/n-GaAs Schottky barrier diodes with and without SiO2 insulator layer at room temperature

In this study, our main goal is fabricated with and without insulator layer Au/n-GaAs Schottky barrier diodes (SBDs) to explain whether or not the insulator layer is effective on some electric parameters such as Φ_B, n, N_ss, and R_s. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-semiconductor (Au/n-GaAs) are investigated and compared with metal-insulator-semiconductor (Au/SiO₂/n-GaAs) Schottky diodes. From the room temperature I-V characteristics of these devices, the main electrical parameters such as, ideality factor (n) and zero bias barrier height (Φ_bo) values of 1.25 and 0.73 eV for Au/n-GaAs, and 1.51 and 0.75 eV for Au/SiO₂/n-GaAs, were obtained. The interface distribution profile (N_ss) as a function of (E_c − E_ss) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_e) and series resistance (R_s) for the Schottky diodes. The N_ss values obtained taking into account the series resistance values are lower than those obtained without considering the series resistance. The diodes show non-ideal I-V behavior with ideality factor greater than unity. This behavior is attributed to the interfacial insulator layer and the interface states. The I-V characteristics confirmed that the distribution of N_ss, R_s, and interfacial insulator layer are important parameters that influence the electrical characteristics of metal-semiconductor and metal-insulator-semiconductor Schottky diodes.     

Effect of strong illumination on current-voltage characteristics of Au/Si, Al/Si and Sn/Si Schottky barriers with native oxide layer

Light induced general degradation in the dark I–V characteristics of Au/Si, Al/Si and Sn/Si junctions at low temperature and at room temperature. Illumination caused changes in the interface and bulk properties of the investigated junctions, all of them prepared under identical conditions. Their barrier heights, φB change with increasing illumination time. The largest rate of degradation in φB upon exposure to light was observed for an Sn/Si junction (lowest φB), whereas the smallest change occurred with an Au/Si junction (highest φB). At low temperature, upon turning off the light, the photogenerated current of the Sn/Si sample exhibited faster recovery in reaching the initial dark current (at till=0) than the Al/Si junction; for the less reactive Au/Si sample, the presence of the oxide layer reduced the leakage current and subsequently delayed recovery of the measured photocurrent. This revised version was published online in August 2006 with corrections to the Cover Date.     

The temperature profile and bias dependent series resistance of Au/Bi4Ti3O12/SiO2/n-Si (MFIS) structures

The Bi₄Ti₃O₁₂ (BTO) thin film were fabricated on an n-type Si substrate and annealed by rapid thermal annealing methods. The temperature dependence of capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the Au/Bi₄Ti₃O₁₂/SiO₂/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structures was investigated by taking the effects of series resistance (R_s) and interface states (N_ss) in the temperature range of 80-400 K. Both the density of interface states N_ss and series resistance R_s were found to be strongly temperature dependent. It is observed that the C-V and G/ω-V plots exhibit anomalous peaks at forward bias because of the influences of N_ss and R_s. It has been experimentally determined that these peak positions shift from accumulation to inversion region, and the maximum values of the capacitance (C) and conductance (G) generally increase with temperature. Also, the distribution profile of R_s-V shows a peak in the accumulation region. The effect of R_s on the C and G is more pronounced in the studied temperature range. The experimental C-V-T and G/ω-V-T characteristics of MFIS structures show the expected behavior due to N_ss in equilibrium with the semiconductor. The temperature dependent C-V and G/ω-V characteristics confirm that the R_s and N_ss play an important role and strongly affect the electrical parameters of MFIS structure.     

Analysis of current-voltage and capacitance-voltage-frequency characteristics in Al/p-Si Schottky diode with the polythiophene-SiO2 nanocomposite interfacial layer

The current-voltage characteristic of the prepared Al/Polythiophene-SiO₂/p-Si Schottky diode was analyzed by using different methods at room temperature. The barrier height and ideality factor of the diode were determined by using the conventional current-voltage method as 0.729 eV and 2.12, respectively. The barrier height values calculated by means of the modified Norde functions have showed good agreement with the barrier height value obtained by using the current-voltage method. The series resistance which causes the electrical characteristics to be non-ideal was calculated from Cheung functions and the modified Norde functions. The energy distribution of the interface states has been determined from the forward-bias current-voltage data. The frequency dependence of the Schottky diode parameters obtained from capacitance-voltage characteristics has been analyzed.     

Effects of pre-annealing conditions on the characteristics of ZnO nanorods and ZnO/p-Si heterojunction diodes grown through hydrothermal method

Pre-annealing of seed layers before the growth of ZnO nanorods (NRs), at various temperatures (non-annealing ~ 800 °C) and in various atmospheres (vacuum, N₂, or O₂), was systematically studied to investigate the effects of pre-annealing on the material properties of ZnO NRs as well as the rectifying behaviour of ZnO NRs/p-Si heterojunction diodes (HJDs). A seed layer was initially prepared on the Si substrate through hydrothermal (HT) method and subsequently pre-annealed; finally, the ZnO NRs were grown through the same HT method. We found that without the annealed seed layer, the ZnO NRs cannot be grown on the Si template and increase in the pre-annealing temperature led to better crystallization and fewer defect-centres in ZnO NRs. However, at a high pre-annealing temperature, the characteristics of ZnO NRs degraded due to the evaporation of oxygen atoms, resulting in more oxygen-vacancy-related defects. The smallest diameter and shortest length of ZnO NRs were observed on the samples pre-annealed at 450 °C. The short length of ZnO NRs implies a slow growth rate, because of which the NRs have sufficient time to align normal to the surface of the substrate. When the seed layer is pre-annealed in an O₂ atmosphere, the oxygen atoms fill the oxygen-vacancy-related defects, which lead to a higher nucleation density and improved characteristics of ZnO NRs. This leads to an extremely high rectification ratio of 1.8 × 10⁵ in ZnO NR/p-Si HJDs. The related mechanisms were explored in this study.     

Surface poisoning in the nucleation and growth of palladium atomic layer deposition with Pd(hfac)2 and formalin

Palladium (Pd) atomic layer deposition (ALD) can be performed with Pd(hfac)₂ (hfac = hexafluoroacetyl-acetone) and formalin as the reactants. For Pd ALD on oxide surfaces, the nucleation of Pd ALD has been observed to require between 20 and 100 ALD cycles. To understand the long nucleation periods, this study explored the surface reactions occurring during Pd ALD nucleation and growth on hydroxylated Al₂O₃ substrates. In situ Fourier transform infrared (FTIR) spectroscopy on high surface area nanopowders was used to observe the surface species. The adsorption of Pd(hfac)₂ on hydroxylated Al₂O₃ substrates was found to yield both Pd(hfac)* and Al(hfac)* surface species. The identity of the Al(hfac)* species was confirmed by separate FTIR studies of hfacH adsorption on the hydroxylated Al₂O₃ substrates. Isothermal loss of the Al(hfac)* species revealed second-order kinetics at 448-523 K with an activation barrier of E_d = 39.4 kcal/mol. The lack of correlation between Al(hfac)* and AlOH* species during the loss of Al(hfac)* species suggested that the Al(hfac)* species may desorb as Al(hfac)₃. After Pd(hfac)₂ exposure and the subsequent formalin exposure on hydroxylated Al₂O₃ substrates, only hfac ligands from Pd(hfac)* species were removed from the surface. In addition, the formalin exposure added formate species. The Al(hfac)* species was identified as the cause of the long nucleation period because Al(hfac)* behaves as a site blocker. The surface poisoning by Al(hfac)* species was corroborated by adsorbing hfacH prior to the Pd(hfac)₂ exposures. The amount of Pd(hfac)* species after Pd(hfac)₂ exposures decreased progressively versus the previous hfacH exposure. Pd ALD occurred gradually during the subsequent Pd ALD cycles as the Al(hfac)* species were slowly removed from the Al₂O₃ surface. Ex situ transmission electron microscopy analysis revealed Pd nanoclusters that grew in size and dispersion with increasing number of Pd ALD cycles. These nanoclusters eventually coalesced to form a continuous Pd ALD film. Surface poisoning by the hfac ligands may help to explain the nucleation difficulties for metal ALD on oxide substrates using β-diketonate reactants.     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.