What Are Power Semiconductor Devices?

Power semiconductor devices are solid-state electronic components designed to control or convert electric power at voltage and current levels far above those handled by signal-processing circuits. Where a logic transistor might switch microamps at a few volts, a power device may block kilovolts and conduct hundreds of amperes. The defining engineering challenge is combining low conduction losses, fast switching speed, and high voltage-blocking capability in a single device structure, three properties that conventional silicon physics forces into trade-offs with one another.

These devices form the active switching elements in inverters, motor drives, power supplies, and grid-connected converters. Their performance characteristics directly determine the efficiency, size, and cost of the power electronics systems that depend on them. Research into new device structures and wide-bandgap semiconductor materials has made improving these trade-offs one of the most active areas in electrical engineering. The IEEE Electron Devices Society publishes extensively on device physics, fabrication, and characterization for power applications.

MOSFETs and Power Transistors

The power metal-oxide-semiconductor field-effect transistor (MOSFET) is the dominant device in low- to medium-voltage applications, particularly in switch-mode power supplies and motor drives rated below a few hundred volts. Its key advantage is voltage-controlled gate operation, which requires minimal drive power and enables very fast switching, reducing switching losses and allowing converters to operate at high frequencies. Higher switching frequency, in turn, allows the passive components (inductors and capacitors) in a converter to shrink, reducing overall system size and weight. Bipolar power transistors preceded MOSFETs in many of these roles and are still encountered in legacy equipment, though they have largely been displaced in new designs.

IGBTs

The insulated-gate bipolar transistor (IGBT) combines the easy voltage-driven gate of a MOSFET with the low forward voltage drop of a bipolar transistor, making it the preferred switch for medium- to high-voltage applications such as traction drives, industrial inverters, and grid-tied renewable energy converters rated from several hundred volts to several kilovolts. IGBTs are packaged in modules that integrate multiple chips, freewheeling diodes, and thermal interfaces into a single assembly. The device has been refined over multiple generations, with each generation improving trade-offs between switching speed and conduction loss. Infineon Technologies maintains detailed application notes on IGBT selection and gate driver design that are widely used in industry.

Schottky Diodes

Schottky diodes are formed at a metal-semiconductor junction rather than a p-n junction, which eliminates the minority-carrier storage effect responsible for the reverse-recovery current that slows down conventional diodes. Faster recovery reduces switching losses in rectifier and freewheeling applications. Silicon Schottky diodes are common in low-voltage power supplies; silicon carbide Schottky diodes extend this fast-recovery advantage to blocking voltages above 600 V, a range where silicon Schottky structures are not feasible.

Silicon Carbide and Wide-Bandgap Devices

Silicon carbide (SiC) and gallium nitride (GaN) are wide-bandgap semiconductors that can sustain much higher electric fields than silicon before avalanche breakdown. This property allows SiC and GaN devices to achieve a given blocking voltage with a thinner, more lightly doped drift region, which reduces on-resistance and switching losses simultaneously. SiC MOSFETs and SiC Schottky diodes are now commercially established in applications such as electric vehicle onboard chargers, photovoltaic inverters, and railway traction. GaN devices are advancing rapidly in the sub-650 V range. The U.S. Department of Energy's Advanced Manufacturing Office has funded wide-bandgap power electronics programs aimed at reducing costs and improving reliability.

Applications

• Motor drives for electric vehicles, industrial machinery, and HVAC systems
• Grid-tied inverters for solar photovoltaic and wind generation plants
• Switch-mode power supplies in servers, telecommunications equipment, and consumer electronics
• Railway traction converters and onboard power systems
• High-voltage direct current converter stations for long-distance power transmission
• Solid-state circuit breakers and fault current limiters in smart grid infrastructure