Technology Advances
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TECHNOLOGY ADVANCES
Low-Cost GaN Schottky Diodes Deliver SiC Performance In the last decade, the wide-bandgap semiconductors silicon carbide (SiC) and gallium nitride (GaN) have become of interest for applications in high-voltage and radio-frequency (rf) switching power devices because of their superior electrical properties. Currently, SiC is commercialized in high-voltage power devices, while GaN is mainly utilized in rf power devices. However, the properties of GaN, such as high breakdown electric field (35 × 105 V/cm, compared with 6 × 105 V/cm for Si), high saturation electron drift velocity (1.5 × 107 cm/s, compared with 1 × 107 cm/s for Si), high electron mobility, and high thermal conductivity make GaN competitive with SiC for high-voltage devices such as Schottky diodes (semiconductor diodes with very fast switching times and a low forward voltage drop and hence very small conduction losses). In addition, the currently available 600 V SiC Schottky diodes are too costly for wide acceptance in the power supply industry. To take advantage of the superior properties of GaN for computer and telecommunications equipment power supplies, Velox Semiconductor is developing innovative AlGaN/ GaN Schottky diodes that have the same or better performance than SiC diodes but are considerably cheaper. Velox Semiconductor grows high-quality, crack-free AlGaN/GaN films with uniform thickness, controlled doping, and low-defect density on sapphire or Si substrates. Three factors—the semiconductor material’s high breakdown electrical field, the epitaxial layer doping, and the
epitaxial layer thickness (2–15 μm)—play critical roles in determining a Schottky diode’s breakdown voltage and forward voltage drop. A low forward voltage drop indicates that conduction losses are very small when switching polarity. To achieve the predicted GaN Schottky diode performance of >5000 V breakdown voltage requires optimizing material growth, device design, and device fabrication. In the reverse current–voltage characteristics of a Velox GaN Schottky diode, the leakage current is 180 μA under a reverse bias of 600 V at room temperature and climbs to 1.4 mA at an elevated temperature of 125°C. The same GaN Schottky diode’s forward current–voltage characteristics demonstrates nearly ideal diode characteristics. (The Schottky ideal factor is close to 1, which indicates that electron transport at the junction between the Schottky metal and the GaN semiconductor is behaving as theoretically predicted.) The forward drop voltage is 1.8 V at 8 A forward current at 25°C and increases to
Technology Advances provides upto-date reports of materials developments that show potential to bridge the gap between research innovation and application of advanced materials technologies. If you encounter or are involved with materials research that shows potential for commercialization and would like to present these developments, contact Renée G. Ford, Renford Communications, [email protected].
2.2 V at 125°C, indicating good forward voltage at elevated temper
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