Modern civilization is related to the increased use of electric energy for industry production, human mobility, and comfortable living. Highly efficient and reliable power electronic systems, which convert and process electric energy from one form to the other, are critical for smart grid and renewable energy systems. The power semiconductor device, as the cornerstone technology in a power electronics system, plays a pivotal role in determining the system efficiency, size, and cost. Starting from the invention and commercialization of silicon bipolar junction transistor 60 years ago, a whole array of silicon power semiconductor devices have been developed and commercialized. These devices enable power electronics systems to reach ultrahigh efficiency and high-power capacity needed for various smart grid and renewable energy system applications such as photovoltaic (PV), wind, energy storage, electric vehicle (EV), flexible ac transmission system (FACTS), and high voltage dc (HVDC) transmission. In the last two decades, newer generations of power semiconductor devices based on wide bandgap (WBG) materials, such as SiC and GaN, were developed and commercialized further pushing the boundary of power semiconductor devices to higher voltages, higher frequencies, and higher temperatures. This paper reviews some of the major power semiconductor devices technologies and their potential impacts and roadmaps.

Power Semiconductor Devices for Smart Grid and Renewable Energy Systems

The use of one or more floating field limiting rings reduces the adverse effect of junction curvature on the breakdown voltage in planar devices. Although this has been known for some time, there has not been a way of accurately predicting the amount of improvement that can be achieved using field rings. In this paper, a computer algorithm is presented which makes it possible to perform field calculations on devices with floating field rings. In addition, a normalized curve is presented which shows the relative improvement that a single optimally placed field ring has on the breakdown voltage for any planar device. The basis of the construction of this curve is the use of a normalized radius of curvature which is a precise measure of the effect of curvature for any device. The theoretical predictions are compared with experiments for over 640 devices encompassing 16 different field ring locations. Good agreement is achieved between theory and experiment.

Theory and breakdown voltage for planar devices with a single field limiting ring

# Avalanche Multiplication # Static Avalanche Breakdown # Avalanche Injection # Dynamic Breakdown

Breakdown Phenomena in Semiconductors and Semiconductor Devices

This chapter intends to provide a comprehensive and comparative discussion of various important power device technologies which are critical for industrial, smart grid and renewable energy applications. A power semiconductor switch is a three‐terminal device that can either conduct a current when it is commanded ON, or block a voltage when it is commanded OFF through the control terminal. Modern power converters require the power device to switch at high frequencies. A modern power semiconductor device operates between ON and OFF states at a high switching frequency. One way to compare state‐of‐the‐art power devices, especially their commercial readiness, is to compare their absolute voltage and current ratings. The chapter reviews several important innovations in Si power devices. The most exciting development in power semiconductor devices in the last decade is the commercialization of a number of wide bandgap power devices.

Power semiconductor devices for smart grid and renewable energy systems

We have fabricated high quantum efficiency, high‐gain (≊5500) avalanche photodiodes with long‐wavelength sensitivity up to λ = 1.7 μm. The primary dark current density at breakdown is JPR⩽8×10−5 A/cm2 with no evidence for tunneling leakage prior to avalanche. To fabricate avalanche photodiodes with no tunneling leakage and high photoresponse at breakdown, we find that the total number of fixed charges in the n‐InP layer must lie in the range of 2×1012 cm−2⩽σB⩽3×1012 cm−2.

A high gain In0.53Ga0.47As/InP avalanche photodiode with no tunneling leakage current

A new method for investigating the field distribution near the surface of p-n junctions is presented. The results show that for negatively beveled junctions, an absolute field maximum exists underneath the surface. This field maximum rather than the field on the surface determines the breakdown voltage of the device. The dependency of the maximum field on various device parameters as base resistivity, bevel angle, and steepness of the doping profile is analyzed. In addition, the influence of surface charges and dielectrics is investigated. Finally, the advantages of positive bevel angles with respect to negative ones are demonstrated. The theoretical results were verified by potential probing measurements on the surface of high-voltage devices.

Field distribution near the surface of beveled P-N junctions in high-voltage devices

A theoretical analysis is made of the field distribution near the surface of p-n-p structures with double positive edge geometry. This geometry offers in principle the possibility of avoiding the limitations and disadvantages inherent in the use of negative bevel angles. The results show that the reduction of the maximum field at the surface is not as easy as for the case of a simple positive bevel angle and that consequently the passivation of the surface may present more problems. Nevertheless, it is demonstrated that this geometry offers a number of great advantages and presents a real alternative for use in future high-voltage devices. A number of devices, dimensioned for a breakdown voltage of 6 kV, were made with this edge geometry. The measurements show that the reverse current corresponds to the thermally generated current in the space-charge layer and that no significant current flows at the surface. The breakdown voltage corresponds to the theoretical breakdown voltage in the bulk, unlike in the case of double negative beveling. The advantages of this geometry with respect to the conventional negative bevel angle are no significant reduction of active area, no dependence on the doping profile, and no limitation in voltage. A disadvantage, however, is the presence of higher fields at the surface.

Double positive beveling: A better edge contour for high-voltage devices

Analytical solutions for the forward characteristic of thyristors have been limited to abrupt and constant doping profiles. Average values for the mobilities and the carrier lifetime had to be assumed for each region of the device. Results will be presented here which are based on an exact numerical solution of the transport, continuity, and Poisson equations for the one-dimensional thyristor. Doping, mobility, and lifetime can be varied from point to point. Thyristor structures are much wider and higher doped than the devices treated numerically in the literature. The dependency of the forward characteristic on various device parameters was examined, and the important results were verified experimentally. For high current and a base width that is large compared to the diffusion length, the dependency of mobility on the carrier concentration leads to a base voltage drop significantly lower than that expected from analytical theory. Furthermore, it is shown that for this case the parameters of the highly doped side regions (doping, width, and lifetime) have much less influence than predicted from Herlet's [3] theory.

Numerical investigation of the thyristor forward characteristic

Experience with beveled p-n junctions does not fully agree with the predictions of Davies and Gentry. Specifically no optimum negative angle as claimed by Huth and Davies was found. A new method for determining the form of the space charge region near the surface shall be presented which avoids the insufficiencies of the model cited. Apart from more accurate results, this paper gives insight into an entirely new phenomenon. In contrast to conventional theory p-n junctions with small negative bevel angles exhibit an absolute electric field maximum underneath the surface. This effect causes a reduction of the breakdown voltage even when the electric field on the surface is sufficiently small. Results will be presented which show the dependency of the absolute field maximum on bevel angle, doping profile and material resistivity. It will be shown that a limit for the use of negative bevel angles exists at about 4 kV breakdown voltage. These theoretical predictions are in excellent agreement with potential probing experiments. Results will also be presented on the influence of dielectrics or charges on the surface.

http://ieeexplore.ieee.org/iel5/9938/31706/01477179.pdf

Field distribution near the surface of beveled P-N junctions in high voltage devices

Analytical solutions for the forward characteristic of thyristors have been presented in the literature. All of them are limited to abrupt and constant doping profiles. Average values for the mobilities and the carrier lifetime have to be assumed for each region of the device. Results will be presented here which are based on an exact numerical solution of the transport, continuity and Poisson equations for the one-dimensional thyristor. Doping, mobility and lifetime can be varied from point to point. Thyristor structures are much longer and higher doped than the devices treated numerically in the literature. The number of iterations necessary to obtain an exact solution can still be kept within reasonable limits by starting from an analytical solution. For this a new analytical approximation for the space charge layers under high injection conditions had to be developed. The dependency of the forward characteristic on various device parameters was examined, and the important results were verified experimentally.

http://ieeexplore.ieee.org/iel5/9937/31693/01476752.pdf

J. Cornu

Papers

Field distribution near the surface of beveled P-N junctions in high-voltage devices

Double positive beveling: A better edge contour for high-voltage devices

Numerical investigation of the thyristor forward characteristic

Field distribution near the surface of beveled P-N junctions in high voltage devices

Numerical investigation of the thyristor forward characteristic