Fortunato Pezzimenti

An Analytical Model of the Forward I– V Characteristics of 4H-SiC p-i-n Diodes Valid for a Wide Range of Temperature and Current

The forward I-V characteristics of 4H-SiC p-i-n diodes are studied in a wide range of currents and temperatures by means of an analytical model that allows us to highlight the minority current contributions in various diode regions, namely, the highly doped regions, the neutral base, and the space charge layer. By accounting for the doping dependence of various physical parameters, such as bandgap narrowing, incomplete doping activation, carrier lifetime, and mobility, the model turns useful to investigate the role of various material properties at different current levels and temperatures. The accuracy of the model is verified by comparisons with numerical simulations and experimental data in a wide range of currents and temperatures, so that this model turns very useful for better understanding the impact of technological parameters on the steady-state behavior of diodes and obtaining an accurate circuital model of diodes.

Simulation and experimental results on the forward J-V characteristic of Al implanted 4H-SiC p-i-n diodes

In this work the forward J-V characteristics of 4H-SiC p-i-n diodes are analysed by means of a physics based device simulator tuned by comparison to experimental results. The circular devices have a diameter of 350@mm. The implanted anode region showed a plateau aluminium concentration of 6x10^1^9cm^-^3 located at the surface with a profile edge located at 0.2@mm and a profile tail crossing the n-type epilayer doping at 1.35@mm. Al atom ionization efficiency was carefully taken into account during the simulations. The final devices showed good rectifying properties and at room temperature a diode current density close to 370A/cm^2 could be measured at 5V. The simulation results were in good agreement with the experimental data taken at temperatures up to about 523K in the whole explored current range extending over nine orders of magnitude. Simulations also allowed to estimate the effect of a different p^+ doping electrically effective profile on the device current handling capabilities.

High-Performance Temperature Sensor Based on 4H-SiC Schottky Diodes

A high-performance temperature sensor based on coupled 4H-SiC Schottky diodes is presented. The linear dependence on temperature of the difference between the forward voltages appearing on two diodes biased at different constant currents, in a range from 30 °C up to 300 °C, was used for temperature sensing. A high sensitivity of 5.11 mV/°C was measured. This is, to the best of our knowledge, the first experimental result about a proportional-to-absolute-temperature sensor made with SiC diodes, showing both a good degree of linearity and long-term stability performance.

Modeling of the Steady State and Switching Characteristics of a Normally Off 4H-SiC Trench Bipolar-Mode FET

The electrical characteristics of a normally off 4H-silicon carbide (SiC) bipolar-mode FET are investigated by means of a careful design activity and an intensive simulation study useful for a first-time-ever realization of this device in SiC. Specific physical models and parameters strictly related to the presently available 4H-SiC technology are taken into account. The device basically consists of a trench vertical JFET operating in the bipolar mode that takes full advantage of the superior material properties. A drain-current density up to 500 A/cm2, a forced current gain on the order of 50, and a specific on-resistance as low as 1.3 mΩ·cm2 are calculated for a 1.3-kV blocking voltage device. The turn-off delay is on the order of a few nanoseconds. The presented analysis is supported by experimental results on the p-i-n diodes embedded in the device structure.

Numerical Simulations of a 4H-SiC BMFET Power Transistor with Normally-Off Characteristics

A numerical simulation study focused on an oxide-free 4H-SiC power device that is based on a normally-off Bipolar Mode Field Effect Transistor (BMFET) structure, and therefore on the principle of conductivity modulation from minority carrier injection, is presented. Starting from a n-/n+ 4H-SiC epi-wafer, with an epitaxial layer thickness of a few microns, and considering the presently available 4H-SiC ion implantation technology, a completely planar SiC-based BMFET has been designed. Such a device has interesting features in terms of static forward and blocking I V characteristics for high power applications. The 4H-SiC fundamental physical models, such as the doping incomplete ionization and the carrier recombination processes, were taken into account during the simulations.

Analytical model for the forward current of Al implanted 4H-SiC p-i-n diodes in a wide range of temperatures

The forward J-V characteristics of 4H-SiC p-i-n diodes are investigated in a wide range of currents and temperatures by means of an analytical model which describes in detail the role of the various physical parameters, such as bandgap narrowing effect, incomplete doping activation and doping-dependent mobility. In order to analyze the influence of the SiC properties at different injection regimes, the total diode current is expressed in terms of the minority current contributions in the various device regions. The accuracy of the model is verified by comparisons with numerical simulations and experimental data reported in the literature. The analysis shows that the proposed model can turn useful for a better understanding of the device behavior and for implementation in circuit simulators.

Analysis of the Forward I – V Characteristics of Al-Implanted 4H-SiC p -i- n Diodes with Modeling of Recombination and Trapping Effects Due to Intrinsic and Doping-Induced Defect States

In this paper, the impact of silicon carbide intrinsic defect states, such as Z1/2 and EH6/7 centers, on the forward current–voltage curves of aluminum (Al)-implanted 4H-SiC p-i-n diodes is investigated by means of a physics-based device simulator. During the simulations, an explicit carrier trap effect due to an electrically active defect concentration produced by the Al+ ion implantation process in the anode region was also taken into account. The obtained current–voltage characteristics are compared with those measured experimentally for several samples at different current levels. It is found that intrinsic defect densities as high as the epilayer doping may lead to undesirable device properties and instability of the forward bias behavior. The diode ideality factor and the series resistance increase with the increase of defects and could be controlled by using high-purity epi-wafers. Furthermore, due to their location in the bandgap and capture cross-sections, the impact of Z1/2 centers on the device electrical characteristics is more severe than that of EH6/7 centers.

Design and numerical characterization of a low voltage power MOSFET in 4H-SiC for photovoltaic applications

Higher efficiency in photovoltaic (PV) conversion calls for the use of small Maximum Power Point Trackers (MPPT) to be placed on board the PV modules. Such circuits require in turn power transistors with low energy losses, high switching speed and blocking voltages lower than 150 V. Thus, starting from a conventional 4H-SiC power MOSFET, a novel device for photovoltaic applications has been designed and numerically simulated in order to determine its on-state resistance (RON) for different device structures and bias voltages. The resulting value of RON is compared to that of a commercial Si-based MOSFET performing the same breakdown voltage.

Numerical simulations of the electrical transport characteristics of a Pt/n-GaN Schottky diode

In this paper, using a numerical simulator, we investigated the current–voltage characteristics of a Pt/n-GaN thin Schottky diode on the basis of the thermionic emission (TE) theory in the 300 to 500 K temperature range. During the simulations, the effect of different defect states within the n-GaN bulk with different densities and spatial locations is considered. The results show that the diode ideality factor and the threshold voltage decrease with increasing temperature, while at the same time, the zero-bias Schottky barrier height (Φb0) extracted from the forward current density–voltage (J–V) characteristics increases. The observed behaviors of the ideality factor and zero-bias barrier height are analyzed on the basis of spatial barrier height inhomogeneities at the Pt/GaN interface by assuming a Gaussian distribution (GD). The plot of apparent barrier height (Φb,App) as a function of q/2kT gives a straight line, where the mean zero-bias barrier height () and the standard deviation (σ0) are 1.48 eV and 0.047 V, respectively. The plot of the modified activation energy against q/kT gives an almost the same value of and an effective Richardson constant A* of 28.22 A cm−2 K−2, which is very close to the theoretical value for n-type GaN/Pt contacts. As expected, the presence of defect states with different trap energy levels has a noticeable impact on the device electrical characteristics.

Static and transient analysis of a 4H-SiC trench Bipolar Mode FET with normally-off characteristics

Steady-state and switching characteristics of a normally-off 4H-SiC Bipolar Mode FET (BMFET) are investigated in a wide range of temperatures by means of an intensive simulation analysis useful for a first time ever realization of this device in SiC. An output drain current density up to 500 A/cm2, an high current gain and an on-resistance as low as 2 mΩ·cm2, are calculated when the gate regions are forward biased. The turn-off delay is in the order of 5 ns and the blocking voltage is higher than 1.2 kV. This study is supported by experimental data on the gate-drain and gate-source p-i-n diodes embedded in the BMFET structure.