Interface roughness scattering in ultra-thin N-polar GaN quantum well channels

In this Letter, we report experimental and theoretical investigations on the effect of the channel thickness on the low-field electron mobility in N-polar GaN quantum well channels. From temperature dependent Hall mobility data and numerical modeling of the mobility, the interface roughness is identified as a strong factor in determining the low field mobility as the channel thickness is scaled down. In the graded AlGaN back-barrier N-polar GaN field effect transistor structures studied here, the roughness leads to localization of electrons at a channel thickness of 3.5 nm leading to extremely low mobility.