Si$_3$N$_4$ layers for the in-situ passivation of GaN-based HEMT structures

A method for the in situ passivation of GaN-based structures with silicon nitride in the growth chamber of a metal organic vapor phase epitaxy (MOVPE) reactor is described. The structural and electrical properties of the obtained layers are investigated. The in situ and ex situ passivation of transistor structures with silicon nitride in an electron-beam-evaporation device are compared. It is shown that ex situ passivation changes neither the initial carrier concentration nor the mobility. In situ passivation makes it possible to protect the structure surface against uncontrollable degradation upon the finishing of growth and extraction to atmosphere. In the in situ passivated structure, the carrier concentration increases and the mobility decreases. This effect should be taken into account when manufacturing passivated GaN-based transistor structures.