SiC Materials and Devices

The following sections are included:

• PREFACE

• CONTENTS

This chapter briefly summarizes device-relevant material properties of the wide bandgap semiconductor silicon carbide. The polytypes 4H-, 6H- and 3C-SiC are predominantly considered. These SiC polytypes can reproducibly be grown as single crystals; they have superior electronic and thermal material properties. The conductivity type can be adjusted by shallow donors and acceptors. Special sections are related to the diffusion of dopants, to the impurity conduction, to the minority carrier lifetime and to the different types of traps generated at the interface of thermally grown SiC/SiO₂ structures.

SiC bulk material quality and surface preparation do not satisfy all the requirements for direct device production. It is necessary to have high quality thick epitaxial layers with low background doping concentration for the fabrication of SiC high power, high voltage, high frequency devices. Different aspects of SiC homo- and heteroepitaxial growth are discussed in this chapter. The wafer surface has a large impact on epitaxial layers, heterostructures and finally on device properties. Thus wafer processing before epitaxial growth is discussed in detail.

In this chapter, the most significant results obtained in the last decade in the field of ohmic contacts to SiC are reviewed.

First, the basic concepts related to the physics of ohmic contacts and to the contact resistance measurement techniques are briefly reported.

Then, some aspects concerning the formation of low resistance (10⁻⁵−¹⁰⁻⁶ Ωcm²) ohmic contacts on n-type and for p-type SiC are discussed, focusing on Ni-based and Al/Ti-based contacts.

Examples of innovative applications on practical devices are also reported, as the simultaneous formation of ohmic contacts on n- and p-type SiC for vertical power MOS devices, obtained adding Al to a standard Ni contact, and a single-metal technology for ohmic and rectifying contacts in MESFETs, using Ti or Ni without post-deposition annealing.

This chapter reviews the status of SiC Schottky barrier diode development. The fundamentals of Schottky barrier diodes are first provided, followed by the review of high-voltage SiC Schottky barrier diodes, junction-barrier Schottky diodes and merged-pin-Schottky diodes. The development history is reviewed and the key performance parameters are discussed. Applications of SiC SBDs in power electronics circuits as well as other areas such as gas sensors, microwave and UV detections are also presented, followed by discussion of remaining challenges.

High voltage PiN rectifiers made using conventional semiconductor materials such as Silicon are restricted to less than 20 kHz and less 120°C operation, thereby severely limiting the availability of advanced electronic hardware used for power grid (also called electric utility), energy storage, pulsed power, intelligent machinery and ultra high voltage solid state power conditioning. Such applications require high power density, very high frequency, and high temperature rectifiers to realize reasonably sized systems. SiC PiN Rectifiers are expected to play an enabling role in a variety of such high voltage applications because they have been shown to offer 2 to 3 orders of magnitude faster switching, high junction temperature capability, high current density operation, and much higher power densities as compared to Silicon.

Silicon carbide (SiC) offers significant advantages for microwave high power devises due to its unique electrical and thermal properties. This review presents a summary of the current position in the development of silicon carbide diodes operating at microwave frequencies: varactors, Schottky barrier mixer diodes, p-i-n and IMPATT diodes. Simplified theory of device operation is given for each kind of microwave diodes to derive the figures of merit, to estimate the potential silicon carbide performance for fabrication of these diodes and to compare SiC with conventional semiconductors. These analyses are followed by description of diode design, fabrication and measured characteristics.

The following sections are included:

• Introduction

• Turn-on process in the thyristors

• Steady-state current-voltage characteristics

• Turn-off performances

• Frequency properties

• Critical charge

• Acknowledgments

• References

The following sections are included:

• Introduction and History of the Static Induction Transistor

• Static Induction Transistor Device Structures

• Current-Voltage Characteristics of the Static Induction Transistor

• Static Induction Transistor Applications

• Summary

• Acknowledgements

• References

The following sections are included:

• AUTHOR INDEX