Ammonia source molecular beam epitaxy of ScAlN/GaN HEMTs with AlN exclusion layers

In this work, ScAlN/GaN high electron mobility transistor heterostructures were grown by molecular beam epitaxy with an ammonia source. The impact of inserting an AlN exclusion layer between the ScAlN barrier and the GaN channel is studied. On the one hand, increasing the AlN exclusion layer thickness from 0.15 to 3.5 nm results in an enhancement of the electron mobility from 391 to 921 cm2/V s. On the other hand, the heterostructure containing a 1.5 nm thick AlN layer grown at 800 °C exhibits a mobility of 666 cm2/V s, while that with a 1.6 nm AlN layer grown at a lower temperature reveals a mobility of 1025 cm2/V s, the maximum recorded in this study, which underlines the important role of this parameter.