Barrier properties and current conduction mechanism for metal contacts to lightly and highly doped p-type 4H-SiC

The barrier properties of Ti, Ni and Pt contact to lightly (9×1016 cm-3) and highly (9×1018 cm-3) doped p-type 4H-SiC were investigated. It is found that the barrier heights and ideality factors estimated from thermionic emission model for the lightly doped samples are non-ideal and abnormally temperature dependent. The anomalies have been successfully explained in terms of both pinch-off model and Gaussian distribution of inhomogeneous barrier heights. In addition, the evaluated homogeneous barrier heights are reasonably close to the average barrier heights from capacitance-voltage measurements. For the highly doped samples, thermionic field emission (TFE) is found to be the dominant carrier transport mechanism. The barrier heights estimated from TFE model are temperature independent. If the barrier inhomogeneities and tunneling effects are considered, the experimental results of the samples are in well agreement with the theoretical calculations.

Formation of highly resistive SiO2 nanoparticle layers from the aerosol by electrostatic precipitation at 200 °C: observations on back corona and nanoparticle layer structure

In this study, a flame-generated nm-range SiO2 aerosol (approx. 170 nm median aggregate diameter) is fed into an electrostatic precipitator with an operating temperature of 200 °C. While a highly porous layer of SiO2 nanoparticles (NPs) is deposited by electrostatic precipitation, a decrease of current uptake is observed initially, indicating exceptionally high values of the electric field within the layer (> 100 kV/mm) and of the layer resistivity (> 1013 Ω∙cm). Later a strong (13- to 17-fold) increase of current uptake is observed. Aerosol charge measurements show that charges of opposite polarity are emitted from the NP layer. Investigation of the NP layer by SEM shows that charge-emitting structures with a polarity-dependent morphology develop on an originally homogeneous NP layer. Based on the experimental evidence, the mechanisms of charge emission and structure formation are discussed. Charge emission from the precipitated dust layer is known as back corona in the field of electrostatic precipitation. It appears that the mechanisms of back corona observed with SiO2 NP layers are quite distinct from those observed with µm-range particles. While gas discharges inside the NP layer are suppressed due to small pore size, back corona inside the NP layers is apparently initiated by thermionic field emission of free electrons and secondary electron multiplication within the NP layer.

Modified expressions of field and thermionic-field emission for Schottky barrier diodes in the reverse regime

In this theoretical work, the author has modified the current-voltage relationship of the field and thermionic–field emission models developed by Padovani and Stratton for the Schottky barrier diodes in the reverse bias conditions with account of the image force correction. Considered in this approach has been the shape of Schottky barrier as trapezoidal. The obtained results show a good agreement between current densities calculated within the framework of these developed models and those calculated using the general model.

Electrical Properties of Silicon Nanowires Schottky Barriers Prepared by MACE at Different Etching Time

This article focused on the electrical characterization of silicon nanowires Schottky barriers following structural analysis of nanowires grown on p-type silicon by Metal (Ag) Assisted Chemical Etching (MACE) method distinguished by their different etching time (5min, 10min, 25min). The SiNWs are well aligned and distributed almost uniformly over the surface of a silicon wafer. In order to enable electrical measurement on the silicon nanowires device, Schottky barriers were performed by depositing Al on the vertically aligned SiNWs arrays. The electrical properties of the resulting Al/SiNWs diodes were characterized by current voltage (I-V) and capacity voltage (C-V) measurements. Unlike the conventional Schottky diode, symmetrical current-voltage (I-V) characteristics have been observed with a rectification ratio < 4. The metal-semiconductor-metal (M-S-M) model was used to analyze the (I-V) characteristics by including two Schottky barriers at the interface between metal and SiNWs. The electron transport behavior is explained by the thermionic field emission method (TFE) which added the effect of the tunneling current compared to the conventional thermionic emission theory. The capacitance-voltage C-V characteristics of SiNWs depend on the bias voltage showing that the samples have an obvious space charge region. Symmetric behavior also appears in the C –V curves that confirm the MSM model.

Current Transport Mechanisms in Au-Free Metallizations for CMOS Compatible GaN HEMT Technology

Gallium nitride (GaN) and its AlGaN/GaN heterostructures grown on large area Si substrates are promising systems to fabricate power devices inside the existing Si CMOS lines. For this purpose, however, Au-free metallizations are required to avoid cross contaminations. In this paper, the mechanisms of current transport in Au-free metallization on AlGaN/GaN heterostructures are studied, with a focus on non-recessed Ti/Al/Ti Ohmic contacts. In particular, an Ohmic behavior of Ti/Al/Ti stacks was observed after an annealing at moderate temperature (600°C). The values of the specific contact resistance ρc decreased from 1.6×104 Ω.cm2 to 7×105 Ω.cm2 with increasing the annealing time from 60 to 180s. The temperature dependence of ρc indicated that the current flow is ruled by a thermionic field emission (TFE) mechanism, with barrier height values of 0.58 eV and 0.52 eV, respectively. Finally, preliminary results on the forward and reverse bias characterization of Au-free tungsten carbide (WC) Schottky contacts are presented. This contact exhibited a barrier height value of 0.82 eV.

Current Transport Mechanism in Palladium Schottky Contact on Si-Based Freestanding GaN

In this study, the charge transport mechanism of Pd/Si-based FS-GaN Schottky diodes was investigated. A temperature-dependent current–voltage analysis revealed that the I-V characteristics of the diodes show a good rectifying behavior with a large ratio of 103–105 at the forward to reverse current at ±1 V. The interface states and non-interacting point defect complex between the Pd metal and FS-GaN crystals induced the inhomogeneity of the barrier height and large ideality factors. Furthermore, we revealed that the electronic conduction of the devices prefers the thermionic field emission (TFE) transport, not the thermionic emission (TE) model, over the entire measurement conditions. The investigation on deep level transient spectroscopy (DLTS) suggests that non-interacting point-defect-driven tunneling influences the charge transport. This investigation about charge transport paves the way to achieving next-generation optoelectronic applications using Si-based FS-GaN Schottky diodes.

Ohmic Contacts on p-Type Al-Implanted 4H-SiC Layers after Different Post-Implantation Annealings

This paper reports on the electrical activation and Ohmic contact properties on p-type Al-implanted silicon carbide (4H-SiC). In particular, the contacts were formed on 4H-SiC-implanted layers, subjected to three different post-implantation annealing processes, at 1675 °C, 1175 °C, and 1825 °C. Under these post-implantation annealing conditions, the electrical activation of the Al dopant species increased from 39% to 56%. The Ti/Al/Ni contacts showed an Ohmic behavior after annealing at 950 °C. The specific contact resistance ρc could be lowered by a factor of 2.6 with the increase of the post-implantation annealing temperature. The result can be useful for application in device fabrication. Moreover, the dependence of ρc on the active acceptor concentration followed the thermionic field emission model, with a barrier height of 0.63 eV.

Metal/Semiconductor Barrier Properties of Non-Recessed Ti/Al/Ti and Ta/Al/Ta Ohmic Contacts on AlGaN/GaN Heterostructures

This paper compares the metal/semiconductor barrier height properties of non-recessed Ti/Al/Ti and Ta/Al/Ta contacts on AlGaN/GaN heterostructures. Both contacts exhibited a rectifying behavior after deposition and after annealing at temperatures up to 550 °C. The ohmic behavior was reached after annealing at 600 °C. High-resolution morphological and electrical mapping by conductive atomic force microscopy showed a flat surface for both contacts, with the presence of isolated hillocks, which had no significant impact on the contact resistance. Structural analyses indicated the formation of the Al3Ti and Al3Ta phases upon annealing. Furthermore, a thin interfacial TiN layer was observed in the Ti/Al/Ti samples, which is likely responsible for a lower barrier and a better specific contact resistance (c = 1.6 10−4 Ωcm2) with respect to the Ta/Al/Ta samples (c = 4.0 10−4 Ωcm2). The temperature dependence of the specific contact resistance was described by a thermionic field emission mechanism, determining barrier height values in the range of 0.58–0.63 eV. These results were discussed in terms of the different microstructures of the interfaces in the two systems.