Power Electronics

Gallium Nitride Transistor Breakthrough

Powdec K.K. announced that, together with Sheffield University, they have succeeded in developing breakthrough high voltage Gallium Nitride (GaN) power transistors. This was realized by creating semiconductor hetero-junction structures based on novel principles, which solve the problems of conventional transistors and dramatically improve the transistor performance. In the transistors, current collapse is almost completely eliminated, power losses are reduced and high break-down voltages of more than 1,100 V are realized. These new GaN transistors are suited to be used in a broad range of equipment from inverters in consumer appliances to server power supplies, electric vehicles and industrial motors to lower power use.

Gallium Nitride is a next generation semiconductor that enables power devices to have lower power losses and higher energy efficiency compared to present silicon devices. Together with Powdec's previously announced GaN diodes, these GaN transistors will be core devices enabling an energy efficient, green future.

Up until now GaN HFETs (Heterojunction Field Effect Transistors) with high-voltage, high energy efficiency have been developed, however they suffer from a major problem of current collapse where current decreases and on-resistance increases during operation. To suppress this phenomenon, various techniques have been developed including metal field plates attached to the gate electrode to decrease the electric field and surface passivation to suppress gate leakage; however improvement in device performance is still not sufficient.

In Powdec's breakthrough solution, instead of a conventional metal field plate, which has hit it's limits, a thin film of p-type GaN (p-GaN) is used. Powdec succeeded in realizing a polarization effect in the top and bottom interfaces of the AlGaN (aluminium gallium nitride) layer where equal negative and positive charge is generated, creating a two-dimensional hole gas (2DHG) and two-dimensional electron gas (2DEG) at the interfaces. This polarization effect almost completely suppresses both the current collapse and current leakage at the gate of the HFET. This is a similar effect seen in silicon super junction devices.

The entire length of the gate-drain channel is depleted (high resistance), and the electric field is distributed uniformly along the channel, enabling these GaN transistors to sustain high breakdown voltages.

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