Figure 1: X-section diagram of GaN power transistorJ.W. Roberts, University of Liverpool & P.R. Chalker, S.J. Cho, I.G. Thayne, K.B. Lee, Z. Zaidi, P.A. Houston

GaN is regarded as a promising semiconductor for next generation power electronic devices due to its high critical breakdown field, high maximum operating temperature, and high switching speeds.

Gate dielectrics used in insulated gate transistors based on GaN also need to show good breakdown properties. Atomic layer deposited Al2O3 with its wide band gap, low leakage and high breakdown field is an excellent candidate for this purpose. However, when Al2O3 is directly deposited onto GaN and AlGaN surfaces, it is associated with a high interface trap density of the order of 1013cm-2eV-1 and higher. These interface states give rise to large hysteresis, threshold voltage shifts and trap charging effects which adversely affect device operation.

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