SiC and GaN High-Voltage Power Devices
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SiC AND GaN HIGH-VOLTAGE POWER DEVICES T.P. Chow Rensselaer Polytechnic Institute, Troy, NY 12180-3590, [email protected] ABSTRACT The present status of development of SiC and GaN devices for high-voltage power electronics applications is reviewed. Device structures that are particularly applicable to these two wide bandgap semiconductors are considered and compared to those commonly used in silicon. The simulated and experimental performance of two-terminal rectifiers and threeterminal transistors and thyristors are compared. The effects of material parameters (mobility, ionization coefficients, lifetimes) and defects on device characteristics are pointed out. Similarities and differences between electronic and photonic device development in these semiconductors are discussed.
INTRODUCTION Silicon has long been the dominant semiconductor of choice for high-voltage power electronics applications [1,2]. However, recently, wide bandgap semiconductors, particularly SiC and GaN, have attracted much attention because they are projected to have more than 100 times better performance than silicon [3-6]. The superior physical properties that these semiconductors offer include a lower intrinsic carrier concentration (10 to 35 orders of magnitude), a higher electric breakdown field (4-20 times), a higher thermal conductivity (3-13 times), a larger saturated electron drift velocity (2-2.5 times), when compared to silicon (See Table I). Two more important material properties may also be noted. First, SiC possesses higher minority carrier lifetimes than GaN because SiC has an indirect bandgap. Second, the hole impact ionization coefficient (αp) is larger than the electron one (αn) in both SiC and GaN, unlike silicon (see Figs. 1 and 2). Several figures of merit, specifically to quantify the intrinsic performance potentials of unipolar and bipolar power switching devices, have been proposed [36]. Another figure of merit has been developed for HBTs, but it is intended for high-frequency amplifying applications [7]. Also, GaN has clearly established itself commercially in the display and photonic applications and blue LEDs and lasers made of InGaN are currently available. Furthermore, SiC MESFETs and SITs, GaN MESFETs and AlGaN HEMTs have been experimentally demonstrated at increasingly higher frequencies for microwave applications. In this paper, the device structures suitable for power switching device demonstrations in SiC and GaN will be presented. Simulated or experimental characteristics of selected two- and three-terminal devices will be described. The material and processing issues that are relevant for power device commercialization will be comparatively discussed. DEVICE CHOICES AND STRUCTURES One of the basic building blocks of a power circuit is the half bridge (Fig. 3), in which two parallelly connected pairs of a three-terminal switch and a two-terminal anti-parallel rectifier are connected in series. T1.1.1
Rectifiers High-voltage power Schottky rectifiers offer fast switching speed but suffers from high onstate volta
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