We have investigated self-heating effects and trapping characteristics in tailored normally-off p-GaN/AlGaN/GaN HEMTs. To improve the high-voltage performance, devices were grown with AlGaN or Fe-doped GaN buffer with or without Ar implantation into conductive SiC substrate prior to heterostructure growth. Our transient self-heating analysis indicated almost three-fold higher temperature rise in the transistors with AlGaN buffer compared to devices employing GaN buffer. Surprisingly, the transient self-heating was further increased in devices with AlGaN buffer with Ar implantation into SiC substrate. This effect could be explained by different material parameters of the AlGaN buffer grown on Ar implanted substrate. Modelling indicated AlGaN thermal conductivity to drop from 30 to 15 W/mK for samples without and with Ar implanted into SiC.
To understand the effect of Ar implantation into SiC in more detail, trapping processes were characterized using drain current transient analysis. It revealed appearance of a dominant trapping process (labelled as Tp2 in figure below) in the devices with AlGaN buffer, while being negligible in those with GaN buffer. To localize the trapping centers, drain current transients were measured on devices subjected to step-stress experiment in the off-state. The investigation suggested that dominant trapping centers (Tp2) are located in the AlGaN buffer. This indicates that Ar implantation into SiC substrate influences the density of in-grown defects in the buffer.
Kuzmík, J., Ťapajna, M., Válik, L., Molnár, M., Donoval, D., Fleury, C., Pogany, D., Strasser, G., Hilt, O., Brunner, F., and Wuerfl, J.: Self-heating in GaN transistors designed for high-power operation, IEEE Trans. Electron Dev. 61 (2014) 3429-3434.
M. Ťapajna, et al. In: ASDAM ’14. Eds. J. Breza et al. Piscataway: IEEE 2014. ISBN: 978-1-4799-5474-2, p. 121.