Investigation of pyroelectric polarization effect on GaN MOS capacitors and field-effect transistors

We compared the high temperature electrical characteristics of GaN MOS capacitors and MOSC-HEMTs on sapphire, Si and bulk GaN substrates. From the flatband voltage shift of the capacitors, we extracted a pyroelectric voltage coefficient of 7.4×10⁴ V/m-K and 8.5×10⁴ V/m-K for sapphire and bulk GaN substrates. The complex threshold voltage shift of MOS Channel-HEMTs (MOSC-HEMTs) could be due to the combining effect of interface traps and polarization charges. The field-effect mobility is very insensitive to the temperature below 150°C, then changes more rapidly (T^-1.59 for sapphire substrate and T^0.86 for Si substrate) from 150°C to 250°C, which indicates that it is surface scattering limited at low temperatures and phonon scattering limited at higher temperatures.