International Conference on Solid State Devices and Materials

GaN-based High Electron Mobility Transistors (HEMTs) are now dominating small chargers as well as mobile base-stations. GaN-based HEMT can switch faster with low losses due to an undoped GaN channel without impurity scattering together with very high carrier concentrations from the polarisation charges between the GaN channel and the AlGaN barrier. To improve, one needs to increase the polarisation charge. Our first approach is to replace AlGaN with AlPN. Since P is much larger than N, only 7% of P has the same strain as the typical 30% AlGaN barriers with a fivefold higher sheet carrier density. However, a strong P-N reaction strongly enhances P-on-Al site defects and special growth conditions are needed. The second approach is N-polar AlN substrates on sapphire with a GaN channel. This can deliver the high sheet carrier densities (~4x10¹³ cm^-2) in thin channels on insulating substrate. However, the growth of N-polar AlN is less researched and very challenging in terms of impurities and smooth surfaces.